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diff --git a/32367-8.txt b/32367-8.txt new file mode 100644 index 0000000..ae7f066 --- /dev/null +++ b/32367-8.txt @@ -0,0 +1,7021 @@ +The Project Gutenberg EBook of Outlines of dairy bacteriology, by +H. L. Russell and E. G. Hastings + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Outlines of dairy bacteriology + A concise manual for the use of students in dairying + +Author: H. L. Russell + E. G. Hastings + +Release Date: May 14, 2010 [EBook #32367] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK OUTLINES OF DAIRY BACTERIOLOGY *** + + + + +Produced by Stacy Brown, Peter Vachuska, Julia Miller and +the Online Distributed Proofreading Team at +https://www.pgdp.net + + + + + + + + + + + +OUTLINES + +OF + +DAIRY BACTERIOLOGY + +A CONCISE MANUAL FOR THE USE OF +STUDENTS IN DAIRYING + +BY + +H. L. RUSSELL + +Dean of the College of Agriculture +University of Wisconsin + +AND + +E. G. HASTINGS + +Professor of Agricultural Bacteriology +University of Wisconsin + +_TENTH EDITION_ + +MADISON, WISCONSIN +H. L. RUSSELL +1914 + + + + +Copyright 1914 + +BY + +H. L. RUSSELL AND E. G. HASTINGS + + + + +PREFACE TO THE TENTH EDITION. + + +This text was originally the outgrowth of a series of lectures on +the subject of dairy bacteriology to practical students in the +winter Dairy Course in the University of Wisconsin. The importance +of bacteriology in dairy processes has now come to be so widely +recognized that no student of dairying regards his training as +complete until he has had the fundamental principles of this +subject. + +The aim of this volume is not to furnish an exhaustive treatise of +the subject, but an outline and sufficient detail to enable the +general student of dairying to obtain as comprehensive an idea of +the bacteria and their effects on milk and other dairy products as +may be possible without the aid of laboratory practice. When +possible the dairy student is urged to secure a laboratory knowledge +of these organisms, but lacking this, the student and general reader +should secure a general survey of the field of bacteriology in +relation to dairying. + +In this, the tenth edition, the effort has been made to include all +of the recent developments of the subject. Especially is this true +in regard to the subject of market milk, a phase of dairying that +has gained greatly in importance in the last few years. The changes +in the methods of handling market milk have been marked. The results +of these changes in influencing the quality of milk offered to the +consumer are fully discussed. + + +H. L. R. + +E. G. H. + + + + +CONTENTS + + +Structure, Growth and Distribution of Bacteria 7 + +Methods of Studying Bacteria 20 + +Contamination of Milk 28 + +Infection of Milk with Pathogenic Bacteria 62 + +Fermentations of Milk 82 + +Preservation of Milk 113 + +Bacteria and Butter Making 136 + +Bacteria and Cheese Making 161 + +Bacteria in Market Milk 189 + + + + +CHAPTER I. + +STRUCTURE, GROWTH AND DISTRIBUTION. + + +=Relation of bacteriology to dairying.= The arts which have been +developed by mankind have been the outgrowth of experience. Man +first learned by doing, _how_ to perform these various activities, +and a scientific knowledge of the underlying principles which govern +these processes was later developed. + +The art of dairying has been practiced from time immemorial, but a +correct understanding of the fundamental principles on which the +practice of dairying rests is of recent origin. In working out these +principles, chemistry has been of great service, but in later years, +bacteriology has also been most successfully applied to the problems +of modern dairying. Indeed, it may be said that the science of +dairying, as related to the problems of dairy manufacture is, in +large degree, dependent upon an understanding of bacteriological +principles. It is therefore essential that the student of dairying, +even though he is concerned in large measure with the practical +aspects of the subject, should acquire as complete an understanding +of these principles as possible. + +While bacteriology is concerned primarily with the activities of +those microscopic forms of plant life known as the bacteria, yet the +general principles governing the life of this particular class of +organisms are sufficiently similar to those governing the molds and +other types of microscopic life that affect milk and its products to +make it possible to include all of these types in a general +consideration of the subject. + +=Nature of bacteria.= The vegetable kingdom to which the bacteria +belong consists of plants of the most varying size and nature. Those +of most common acquaintance are the green plants varying in size +from those not visible to the naked eye to the largest trees. +Another class of plants known as fungi or fungous plants do not +contain chlorophyll, the green coloring matter, but are usually +colorless and, as a rule, of small size; among them are included +such forms as the mushrooms, smuts, rusts and mildews, as well as +the molds and yeasts. The bacteria are closely allied to this latter +class. When first discovered they were thought to be animals because +of the ability of some forms to move about in liquids. + +The bacteria, like other kinds of living organisms, possess a +definite form and shape. They are the simplest in structure of all +the plants, the individual organism consisting of a single cell. The +larger and more highly organized forms of life are made up of many +microscopic cells, and the life of the individual consists of the +work of all the cells. The bacteria are very comparable to the +single cells of the higher plants and animals, but in the case of +the bacteria the single cell is able to exist apart from all other +cells and to carry out all of its life processes including +reproduction. + +=Forms of bacteria.= With the multicellular organisms much variation +in form is possible, but with these single-celled organisms the +possible variation in form is greatly limited. Three well marked +types occur among the bacteria: the round or coccus form (plural +cocci); the rod-shaped or bacillus (plural bacilli); and the +twisted or spirillum type (plural spirilla). Most organisms of +special significance in dairying belong to the coccus or bacillus +group. + +=Size of bacteria.= The bacteria, as a class, are among the smallest +of living objects. None of them are individually visible to the +naked eye, and they can be so seen only when clumps or masses are +formed in the process of growth. + +[Illustration: Fig. 1.--Forms of Bacteria. A, coccus; B, bacillus; +C, spirillum.] + +While there is considerable relative variation in size, yet in +actual dimensions, this difference is so small as to make careful +microscopic determinations necessary. An average diameter may be +taken as about one thirty-thousandth of an inch, while the length +varies naturally several fold, depending upon whether the type under +observation is a coccus or a bacillus. + +It is very difficult to conceive of the minuteness of the bacteria; +the following may give some idea of their size. In a drop of cream +ready for churning may be found as many as 10,000,000 and in a piece +of fresh cheese as large as a cherry there may be as many living +bacteria as there are people on our earth. While the bacteria are +very minute, the effect which they exert in milk and other dairy +products is great on account of their enormous numbers. + +=Manner of growth.= The cells of which all plants and animals consist +increase in numbers by the division of each cell into two cells +through the formation of a division wall across the cell. The new +cells divide and the plant or animal continues to grow. The same +cell division occurs in the bacteria but since the bacteria are +single celled, division of the cells means an increase in numbers +rather than growth as in the higher forms of life. + +[Illustration: Fig. 2.--Division of Bacteria. + +The bacteria increase in numbers by the division of each cell into +two cells. (After Novy.)] + +In the case of those bacteria that have a greater length than +diameter, the new wall is formed at right angles to the long axis of +the cell. As soon as the division is complete each cell is a +complete individual, capable of carrying on all of its life +processes. The cells may, however, cohere and thus form distinctive +groupings that may serve to identify certain types. Some of the +cocci form long chains and the term _streptococcus_ is applied to +such. Other groupings may be similar to a bale of twine or they may +be massed in clusters with no regularity distinguishable. + +=Spores.= Just as ordinary plants form resistant structures, known as +seeds, capable of retaining vitality under conditions unfavorable +for growth thereby perpetuating the species, so with certain of the +bacteria, definite structures, known as _spores_, that are analogous +in some respects to the seeds of the higher plants, are produced +within the mother cell. The spores are exceedingly resistant to the +influence of an unfavorable environment, such as heat, cold, drying, +and even chemical agents. It is this property of the spores which +makes it so difficult to destroy the bacterial life in the process +of sterilizing milk. The property of spore-formation is fortunately +confined to a comparatively small number of different species of +bacilli. + +=Movement.= Many of the bacteria are provided with vibratory organs of +locomotion, known as _cilia_ (singular cilium) which are variously +distributed on the surface of the cell. By the movement of these +relatively long, thread-like appendages the individual cell is able +to move in liquids. It must be remembered, when these moving cells +are observed under the microscope, that their apparent rate of +movement is magnified relatively as much as their size. + +=Conditions for growth.= All kinds of living things need certain +conditions for growth such as food, moisture, air and a favorable +temperature. The bacteria prefer as food such organic matter as +milk, meat, and vegetable infusions. Those living on dead organic +matter are known as _saprophytes_, while those which are capable of +thriving in the tissues of the living plant or animal are known as +_parasites_. Certain of the parasitic forms are capable of causing +disease in plants and animals. In the first group are embraced most +of the bacteria that are able to develop in milk or its products, +such as those forms concerned in the spoiling of milk or its +fermentation. It is true that milk may contain disease-producing +bacteria coming either from a diseased animal or from a diseased +human being. It is also true that some of such harmful forms are +able to grow in milk, such as the organisms causing typhoid fever +and diphtheria. + +=Food.= The bacteria like all other plants must have their food in +solution. Where they apparently live on solids, such as meats, +fruits, etc., they dissolve the food substances before utilizing the +same. If the solutions are highly concentrated, as in the case of +syrups, preserves and condensed milk, the bacteria cannot readily +grow, although all of the necessary food ingredients are present. +When such concentrated solutions are diluted, bacterial growth will +take place and the solutions will spoil. + +[Illustration: Fig. 3.--Photomicrograph of Lactic Acid Bacteria. + +Each cell is an individual organism, magnified 1250 diameters.] + +Generally speaking the bacteria grow best in a neutral or slightly +alkaline solution rather than in acid liquids. + +=Temperature.= One of the most important conditions influencing the +rate of growth of bacteria is the temperature. Each form has a +_minimum_ temperature below which growth can not take place; also a +_maximum_ above which growth is again impossible. For the majority +of species the minimum temperature ranges from 40 to 45° F. the +maximum from 105 to 110° F. Growth takes place most rapidly at the +optimum temperature, which, for each species, lies close to the +maximum temperature at which growth can occur. Most of the bacteria +of importance in the dairy grow well at from 70 to 100° F. + +There are forms that can grow below the freezing point of water when +they are in solutions that do not freeze at this temperature. There +are still other bacteria that can grow at 140° F. a temperature that +is quickly fatal to most forms. These are of importance in the dairy +since they limit the temperatures at which milk can be stored for +long periods of time. + +=Air supply.= Living organisms, both plant and animal, require air or +oxygen for the combustion of their food and for the production of +energy. Most bacteria use, as do the green plants and animals, the +free oxygen of the air for their respiration. Such organisms are +called _aerobic_ or air-living. A much smaller group possess the +power of taking oxygen from organic compounds such as sugar and the +like and therefore are able to live under conditions where air is +excluded. These are called _anaerobic_ bacteria. A large number of +bacteria are able to live either in the presence or in the absence +of free oxygen. Most of the bacteria of importance in the dairy are +of this nature. + +=Rate of growth.= When there is an abundant supply of food and when +the temperature conditions are favorable, the bacteria increase in +numbers with astounding rapidity. It has been determined by actual +experiment that the process of cell division under favorable +conditions takes place in a few moments. Barber has shown that one +of the forms of bacteria constantly found in milk will divide in 17 +minutes at 98° F. and that a single organism kept at this +temperature for ten hours would increase to 1,240,000,000. If the +temperature is reduced to 50° F., the time required for division is +increased to several hours. The explanation for the rapid spoiling +of milk that is not well cooled is thus apparent. The initial rapid +rate of increase cannot be maintained for any length of time as the +conditions become more and more unfavorable as growth continues, due +to the accumulation of the by-products of the cell activity. Thus, +the growth of acid-forming organisms in milk becomes checked by the +formation of acid from the fermentation of the sugar. + +=Detrimental effect of external conditions.= Environmental conditions +of a detrimental character are constantly at work tending to repress +the activity of bacteria or to destroy them. These act more readily +on the vegetating cells than on the more resistant spores. It is of +the utmost importance that those engaged in dairy work be familiar +with these antagonistic forces since it is constantly necessary to +repress or to kill outright the bacteria in milk and other dairy +products. In many lines of dairy work it is likewise important to be +familiar with the conditions favorable for bacterial growth. + +=Effect of cold.= While it is true that chilling largely prevents +fermentative action, and actual freezing stops all growth processes, +still it does not follow that exposure to low temperatures will +effectually destroy the vitality of bacteria, even in the growing +condition. Numerous non-spore-bearing species remain alive in ice +for a prolonged period, and experiments with liquid air show that +even a temperature of-310° F. maintained for hours does not kill all +exposed cells. + +=Effect of heat.= High temperatures, on the other hand, will destroy +any form of life, whether in the vegetative or latent spore stage. +The temperature at which the vitality of the cell is lost is known +as the _thermal death point_. This limit is dependent not only upon +the nature of the organism, but upon the time of exposure and the +condition in which the heat is applied. In a moist atmosphere, the +penetrating power of heat is great, consequently cell death occurs +at a lower temperature than in a dry atmosphere. An increase in time +of exposure lowers the temperature point at which death occurs. + +For growing organisms, the thermal death point of most species +ranges from 130° to 140° F. for ten minutes. When spores are +present, resistance is greatly increased, some forms being able to +withstand steam at 212° F. from one to three hours. In the +sterilization of milk, it is often necessary to heat for several +hours, where a single exposure is made, to destroy the resistant +spores, that seem to be more abundant under summer than winter +conditions. Steam under pressure is a much more effective agent, as +the temperature is thus raised considerably beyond 212° F. An +exposure of twenty minutes, at a temperature of 230° to 240° F. will +kill all spores. Where heat is used in a dry state, it is much less +effective, a baking temperature of 260° to 300° F. for an hour being +necessary to kill spores. This condition is of the utmost importance +in the destruction of bacteria in the dairy and creamery. + +=Effect of drying.= The spore-bearing bacteria withstand +effects of desiccation without serious injury, and many of the +non-spore-producing types retain their vitality for some months. The +bacteria found in the air are practically all derived from the soil, +and exist in the air in a dried condition, in which they are able to +remain alive for considerable periods of time. In a dried condition, +active cell growth is not possible, but when other conditions, such +as moisture and food supply are present, resumption of growth +quickly begins. This property is also of importance in the dairy as +in the preparation of dry starters for creameries and cheese +factories. + +=Effect of light.= Bright sunlight exerts a markedly injurious effect +on bacterial life, both in a spore and in a growing condition. Where +the direct sunlight strikes, more or less complete disinfection +results in the course of a few hours, the effect being produced by +the chemical or violet rays, and not by the heat or red rays of the +spectrum. This action, however, does not penetrate opaque objects, +and is therefore confined to the surface. In diffused light, the +effect is much lessened, although it is exerted to some extent. +Sunlight exerts a beneficial effect on the general health and +well-being of animal life, and is a matter of importance to be taken +into consideration in the erection of buildings for animals as well +as for people. + +=Effect of chemicals.= A great many chemical substances exert a more +or less powerful toxic action on various kinds of life. Many of +these are of great service in destroying bacteria or holding them in +check. Those that are toxic and result in the death of the cell are +known as _disinfectants_; those that merely inhibit, or retard +growth are known as _antiseptics_. All disinfectants must of +necessity be antiseptic in their action, but not all antiseptics are +disinfectants, even when used in large amounts. Disinfectants have +no place in dairy work, except to destroy disease-producing +bacteria, or to preserve milk for analytical purposes. The so-called +chemical preservatives used to "keep" milk depend for their effect +on the inhibition of bacterial growth. In this country, most states +prohibit the use of these substances in milk. Their only function in +the dairy should be to check fermentative and putrefactive processes +outside of milk and so keep the air free from taints. + +=Products of growth.= All bacteria, as a result of their growth in +food substances, form more or less characteristic compounds that are +known as _by-products_. The changes brought about are those of +decomposition and are collectively known as _fermentations_; they +are characterized by the production of a large amount of by-products +as the result of the development of a relatively small amount of +cell life. The souring of milk, the rotting of eggs, the spoiling of +meats, the making of vinegar from cider are examples of +fermentations caused by different bacteria. + +If the substances decomposed contain but little sugar, as do animal +tissues, the conditions are favorable for the growth of the +putrefactive bacteria, and foul-smelling gases are formed. When +sugars are present, as in milk, the environmental conditions are +most favorable for the acid-forming bacteria that do not as a rule +produce offensive odors. + +Many of the bacteria form substances known as enzymes which are able +to produce certain decomposition changes in the absence of the +living cells, and it is by virtue of these enzymes that the +organisms are able to break down such enormous quantities of +organic matter. Most of these enzymes react toward heat, cold, +and chemical poisons in a manner quite similar to the living +cells. In one respect, they are readily differentiated, and that +is, that practically all of them are capable of producing their +characteristic chemical transformations under conditions where the +activity of the cell is wholly suspended as in a saturated ether or +chloroform atmosphere. The production of enzymes is not confined to +bacteria, but they are found throughout the animal and plant world, +especially in those processes that are concerned in digestion. +Rennet, used in cheese making, is an example of an animal enzyme. + +=Distribution of bacteria.= As bacteria possess greater powers of +resistance than almost any other form of life, they are found very +widely distributed over the surface of the earth. In soil they are +abundant, because of the fact that all of the conditions necessary +for growth are here best satisfied. They are, however, distributed +with reference to the layers of the soil; the soil proper, i.e., +that turned over by the plow, is extremely rich in them on account +of the abundance of organic matter. But at the depth of a few feet +they decrease rapidly in numbers, and in the deeper layers, from six +to ten feet, or more, they are normally not present, because of the +lack of proper food supply and oxygen. The fertility of the soil is +closely associated with their presence. + +The bacteria are found in the air because of their development in +the soil below. They are unable to grow even in a moist atmosphere, +but are so readily dislodged by wind currents from the soil that +over land areas the lower strata of the air always contain them. +They are more numerous in summer than in winter; city air contains +larger numbers than country air. Wherever dried fecal matter is +present, as in barns, the air contains many forms. + +Water generally contains enough organic matter in solution, so that +certain types of bacterial life find favorable growth conditions. +Water in contact with the soil surface takes up many impurities, and +is of necessity rich in bacteria. As the rain water percolates into +the soil, it loses its germ content, so that the normal ground +water, like the deeper soil layers, contains practically no +bacterial life. Springs, therefore, are relatively deficient in germ +life, except as they become contaminated with soil organisms, as the +water issues from the ground. Wells vary in their germ content, +depending upon manner of construction, ease of contamination at +surface, etc. Wells are too frequently insufficiently protected from +surface leachings, and consequently may contain all kinds of +organisms found in the surface soil. Typhoid fever is very +frequently disseminated in this way, as is cholera and a number of +animal maladies. + +While the inner tissues of healthy animals are free from bacteria, +the natural passages, as the respiratory and digestive tracts, being +in more direct contact with the exterior, become readily infected. +This is particularly true with reference to the intestinal tract, +and in the undigested residue of the food, bacterial activity is at +a maximum. The result is that fecal matter of all kinds contains +enormous numbers of organisms so that the pollution of any food +medium, such as milk, with such material is sure to introduce +elements that seriously affect its quality. + + + + +CHAPTER II. + +METHODS OF STUDYING BACTERIA. + + +=Necessity of artificial cultivation.= The bacteria are so extremely +small, that it is impossible to study individual germs separately +without the aid of powerful microscopes. Little advance was made in +the knowledge of these lower forms of plant life until the +introduction of culture methods, whereby a single organism could be +cultivated, and the progeny of this cell increased to such an extent +in a short course of time that the resulting mass of cells would be +visible to the unaided eye. This is done by growing the bacteria on +various kinds of nutrient media that are prepared for the purpose, +but inasmuch as bacteria are so universally distributed, it becomes +an impossibility to cultivate any special form alone, unless the +medium in which they are grown is first freed from all pre-existing +forms of germ life. + +=Food materials.= Many kinds of food substances are used for the +cultivation of bacteria in the laboratory. In fact, bacteria will +grow on almost any organic substance, whether it is solid or liquid, +provided the other essential conditions of growth are furnished. The +food substances that are used for culture purposes are divided into +two classes,--solids and liquids. + +Solid culture media may be either permanently solid, like potatoes +and coagulated egg, or they may retain their solid properties only +at certain temperatures, like gelatin or agar. The latter two, which +were devised by Robert Koch, are of utmost importance in +bacteriological research, for their use permits the separation of +the different forms of bacteria that may happen to be in any +mixture. Gelatin is advantageously used, because the majority of +bacteria present wider differences, due to growth upon this medium, +than upon any other. It remains solid at ordinary temperatures, +becoming liquid at about 80° F. Agar, a gelatinous product derived +from a Japanese seaweed, has a much higher melting point, and is +used especially with those organisms whose optimum temperature for +growth is above the melting point of gelatin. + +Besides these solid culture media, different liquid substances are +extensively used, such as beef broth, milk and infusions of various +vegetable and animal tissues. Skim milk is of especial value in +studying the milk bacteria, and may be used in its natural +condition, or a few drops of litmus solution may be added, in order +to detect any change in its chemical reaction due to the bacteria. + +=Sterilization.= The various ingredients that are used in the +preparation of culture media are not free from micro-organisms, +hence the media would soon spoil if they were not destroyed, and the +media subsequently protected from contamination from the air, etc. +The process of rendering the media free from living micro-organisms +is known as _sterilization_. It may be accomplished in a number of +ways, but most often is done by the use of heat. For culture +material, which is always organic in character, moist heat is +employed. The various culture media, in appropriate containers, are +subjected to a thorough steaming in a steam cooker. This destroys +all of the vegetating cells but not the resistant spores that may be +present. The media are then stored, for twenty-four hours, at +temperatures favorable for the germination of the spores and are +then again heated. Three such applications on successive days are +usually sufficient to free the media from all living germs, since +between the heating periods the spores germinate and the resulting +vegetative cells are more easily destroyed. The sterile media will +keep for an indefinite period in a moist place. + +The media are usually placed in glass containers which may be +sterilized before use by heating them in an oven, it being possible +to thus secure a much higher temperature than with streaming steam. +All glass or metal articles may be sterilized by the use of dry heat +but for organic media, to avoid burning, moist heat must be used. + +All kinds of materials may be sterilized by treatment with steam +under pressure. An exposure for a few moments at 250° F., a +temperature attained with 15 pounds steam pressure, will destroy all +kinds of bacteria and their spores. This method of sterilization is +used in the canning of meats and vegetables and in the preparation +of evaporated milk. To avoid contamination of the media after +sterilization, the flasks and tubes are, after being filled, +stoppered with plugs of cotton-wool, which effectually filter out +all bacteria and mold spores from the air, and yet allow the air to +pass freely in and out of the containers. + +=Methods of determining the number of bacteria.= The method of +determining the number and kinds of bacteria in any substance can be +illustrated by the process as applied to milk. For this purpose the +method of procedure is as follows: Sterile gelatin in glass tubes is +melted and then cooled until it is barely warm. To this melted +gelatin a definite quantity of milk is added. The medium is gently +shaken, so as to thoroughly mix the milk and gelatine, and the +mixture then poured into a sterile, flat, glass dish, and quickly +covered, where it is allowed to cool until the gelatin hardens. +After the culture plate has been left for twenty-four to thirty-six +hours at the proper temperature, tiny spots will begin to appear on +the surface, or in the depth of the culture-medium. These spots are +called _colonies_, and are composed of an almost infinite number of +individual cells, the result of the continued growth of a single +organism that was in the drop of milk and which was firmly held in +place when the gelatin solidified. The number of these colonies +represents approximately the number of living bacteria that were +present in the amount of milk added to the tube of gelatin. If the +plate is not too thickly sown with the bacteria, the colonies will +continue to grow and increase in size, and as they do, minute +differences will begin to appear. These differences may be in the +color, the contour, and the texture of the colony, or the manner in +which it acts toward gelatin. + +[Illustration: Fig. 4.--Plate Culture. + +Each of the dots is a colony that has been formed by the growth of +an organism embedded in the solid culture-medium. By counting the +colonies, the number of living bacteria in the amount of milk added +to the culture is determined.] + +In order to make sure that the number of colonies is not so numerous +as to prevent counting and further study of their characteristics, a +series of plate cultures is usually made in which varying amounts of +milk are added to the tubes of gelatine. This is attained by adding +a definite amount of the milk or other substance to be examined to a +measured amount of sterile water, e.g., one cubic centimeter of milk +to ninety-nine cubic centimeters of water. One cubic centimeter of +this mixture may be used for the inoculation of the plate culture. +This dilution may be carried on to any desired extent; in the +examination of many dairy products, it is necessary to use very +minute quantities of material, often only one one-millionth of a +cubic centimeter. + +To study further the peculiarities of the different bacteria, small +portions of the individual colonies are transferred to tubes of +sterile culture-media. In order to do this the colony is touched +with a piece of platinum wire; the minute amount of growth that +adheres to the wire is sufficient to seed the tube of fresh +culture-medium. The inoculating needle must always be sterilized +before use by passing it through a gas flame. + +A culture thus obtained is called a _pure culture_ since it contains +but a single kind of an organism, as the colony is the result of the +growth of a single cell. These cultures then serve as a basis for +continued study, and must be planted and grown upon the different +kinds of media that are obtainable. In this way the slightest +variations in the growth of different forms are detected, and the +peculiar characteristics are determined, so that the student is able +to recognize this form when he meets it again. + +[Illustration: Fig. 5.--Different Kinds of Bacteria Growing in +Gelatin. + +A, meager growth, no liquefaction or surface growth; B, profuse +surface growth, radiating filaments from the growth below the +surface; C, a rapid liquefying form; D, a gas producer that grows +equally well in the presence or absence of air; E, form that grows +only in the absence of air, an anaerob.] + +These culture methods are of essential importance in bacteriology, +as it is the only way in which it is possible to secure a quantity +of germs in a pure state. + +=The microscope in bacterial investigations.= In order to verify the +purity of the cultures, the microscope is in constant demand +throughout all the different stages of the isolating process. For +this purpose it is essential that the instrument used shall be one +of high magnifying powers (600 to 800 diameters), combined with +sharp definition. + +The microscopical examination of any germ is quite as essential as +the determination of culture characteristics, in fact, the two must +go hand in hand. The examination reveals not only the form and size +of the individual germs but the manner in which they are united with +each other, as well as any peculiarities of movement that they may +possess. + +In carrying out the microscopical part of the work, not only is the +organism examined in a living condition, but colored preparations +are made by using solutions of anilin dyes as staining agents. These +are of great service in bringing out almost imperceptible +differences. The art of staining has been carried to the highest +degree of perfection in bacteriology, especially in the detection of +germs that are found in diseased tissues in the animal or human +body. + +In studying the peculiarities of any special organism, not only is +it necessary that these cultural and microscopical characters should +be closely observed, but special experiments must be made in +different ways, in order to determine any special properties that +the germ may possess. Thus, the ability of any form to act as a +fermentative organism can be tested by fermentation experiments; the +property of causing disease, studied by the inoculation of pure +cultures into experimental animals, like rabbits, guinea pigs and +white mice. + +The methods of the bacteriologist in his laboratory are in their +effect not dissimilar to those which the farmer employs in securing +his crop of pure-bred grain. The laboratory farmer kills the weed +seeds in his culture field by the application of heat. His field, +which is embraced in his culture dish, has been fertilized and +prepared by the addition of certain favorable ingredients. When he +has garnered his crop, he maintains its purity by keeping his +selected seed, the pure culture, free from all contamination. The +dairyman, even though he may not expect to carry on the detailed +operations of the laboratory, will understand the reason for the +directions which he is often required to follow much better if he +knows how the simple operations of the laboratory are carried out. +For a fuller knowledge of these matters, the reader is referred to +the special texts on bacteriology. + + + + +CHAPTER III. + +CONTAMINATION OF MILK. + + +=Spoiling of milk.= Materials of animal origin are peculiarly prone to +undergo changes, rendering them unfit for use, and of these, milk is +exceedingly susceptible to such changes. This is due to the fact +that the composition of milk is especially adapted to bacterial +growth, and that the opportunity for entrance of such organisms is +likewise such as to permit of abundant contamination. The +consequence is that milk readily undergoes fermentative changes, due +to the development of one or another type of micro-organism. + +=Milk, a suitable bacterial food.= While milk is designed by nature +for the nourishment of mammalian life, it is, curiously enough, +equally well adapted to the growth of these lowest forms of +vegetable life. The nutritive substances required by bacteria are +here sufficiently dilute to make possible rapid growth. + +Milk also contains all the necessary chemical substances to make a +suitable bacterial food supply. Of the nitrogenous compounds, +albumen is in a readily assimilable form. Casein, the principal +nitrogenous constituent of milk, exists in an insoluble condition, +and cannot be directly utilized, until it is acted upon by digesting +enzymes. The fat in milk does not readily decompose, and while there +are a few bacteria capable of splitting this substance, the majority +of organisms are unable to utilize it. Milk sugar, on the other +hand, is an excellent food for most species. + +[Illustration: Fig. 6.--Fat Globules and Bacteria. + +Note the relative size of the fat globules of milk and the lactic +acid bacteria.] + +=Sources of contamination.= Inasmuch as milk is especially exposed to +the inroads of bacterial growth, and because of the fact that much +of the contamination can easily be prevented, it is highly important +that the milk producer and dealer should be thoroughly cognizant of +the various sources of contamination. The different factors +concerned in contamination may be grouped as follows: the interior +of the udder; utensils, including all apparatus with which the milk +is brought in contact subsequent to withdrawal from the animal; +infection coming from the animal herself, from the milker, and the +surrounding air. + +=Condition of milk when secreted.= Immediately after withdrawal from +the udder, milk always contains bacteria, yet in the secreting +cells of the udder of a healthy cow, germ life does not seem to be +present. Only when the gland is diseased are bacteria found in any +abundance. In the passage of the milk from the secreting cells to +the outside, it receives its first infection, so that when drawn +from the animal it generally contains a considerable number of +organisms. + +A study of the structure of the udder shows the manner in which such +infection occurs. + +=Structure of the udder.= The udder is composed of secreting tissue +(_gland cells_) that is supported by fibrous connective tissue. The +milk is elaborated in these cells and is discharged into microscopic +cavities, from whence it flows through the numerous channels (_milk +sinuses_) that ramify through the substance of the udder, until +finally it is conveyed into the _milk cistern_, a common receptacle +holding about one half pint that is located just above the teat. +This cavity is connected with the outside by a direct opening (_milk +duct_) through the teat. During the process of milking, the milk is +elaborated rapidly in the gland cells, and their contents upon +rupture of the milk cells, flow down into the cistern. The normal +contraction of the muscles at the lower opening of the outer duct +prevents the milk from passing out except when pressure is applied, +as in milking. The inner walls of the milk duct and cistern are +always more or less moist, and therefore afford a suitable place for +bacteria to develop, if infection once occurs, and conditions are +favorable for growth. + +=Manner of invasion.= Two possible sources of invasion of the udder by +bacteria may exist. If bacteria are present in the circulating +blood, there is the possibility of organisms passing directly +through the tissues into the milk-secreting cells. The other +alternative is the possible direct contamination from the outside by +organisms passing up through the milk duct, and so spreading through +the open channels in the udder. + +[Illustration: Fig. 7.--Sectional View of Udder. + +Teat with milk duct connecting the exterior with the milk cistern. +Milk sinuses which conduct the milk from the secreting tissue to the +milk cistern. (After Moore & Ward.)] + +=Number of bacteria in fore-milk.= If a bacteriological examination is +made of the milk drawn from each teat at different periods during +the milking process, it will be found that the fore-milk, _i.e._, +the first few streams, contains, as a rule, many more organisms per +cubic centimeter than that removed later. Not infrequently thousands +of organisms per cubic centimeter may be found in the first streams +while the middle milk, or strippings, will contain much smaller +numbers. + +=Distribution and nature of bacteria in udder.= If the udder itself is +carefully examined as to its bacterial content, it appears that the +majority of organisms found is confined to the lower portion of this +organ, in the teat, milk-cistern and large milk-ducts; while +bacteria occur in contact with the secreting tissue, they are +relatively less abundant. This would seem to indicate that the more +probable mode of infection is through the open teat. + +While there is no constant type of bacteria found in the fore-milk, +yet it is noteworthy that nearly all observers agree that the +organisms most commonly found are not usually the acid-producing, or +gas-generating type, so abundant on the skin or hairy coat of the +udder and which predominate in ordinary milks. Coccus forms, +belonging to both liquefying and non-liquefying types are most +generally present. Many of these produce acid slowly and in small +quantities. + +The bacteria coming from the interior of the udder are of small +practical significance since they do not grow rapidly at the +temperatures at which milk is stored. If the milk is protected from +contamination from other sources, the bacteria from the udder will +ultimately cause it to spoil, but under ordinary conditions other +forms are present in such greater numbers, and grow so much more +rapidly in milk, that the udder forms have small opportunity to +exert any effect. + +It is interesting to note that the bacteria found in the udder are +similar to those that seem to be most abundant in such glandular +tissues as the liver and spleen. This fact increases the probability +that these comparatively inert coccus forms of the udder may +originate directly from the blood stream. The organisms that +normally are found in the udder exert no harmful effects on the +gland. It might be thought that due to the presence of abundant food +and a favorable temperature that growth would be abundant, but such +is not the case. At times the udder may be invaded by forms that are +not held in check by the natural factors and an inflammation of the +udder is likely to result. + +=Germicidal property of milk.= It has been claimed that freshly drawn +milk, like other body fluids, possesses germicidal properties, +_i.e._, the power of destroying bacteria with which it may be +brought in contact. If milk is carefully examined bacteriologically, +hour by hour, after it is withdrawn from the udder, it will +generally be found that there is at first not only no increase in +number of organisms during a longer or shorter period when it is +kept at temperatures varying from 40° to 70° F., but that an actual +reduction not infrequently takes place. When cultures of bacteria, +such as _B. prodigiosus_, a red organism, lactic acid organisms, and +even the yellow, liquefying coccus, so commonly found in the +fore-milk, are artificially introduced into the udder, it has been +found that no growth occurs and that in the course of a few days the +introduced organisms actually disappear. Whether this failure to +colonize can be regarded as evidence of a germicidal property or not +is questionable. In fact, this question is a matter of but little +practical importance in the handling of milk since, under the best +of conditions, the keeping quality of the milk is not materially +enhanced. It may be of importance in inhibiting growth in the udder. + +=Rejection of fore-milk.= The fact that the fore-milk contains per +cubic centimeter so much more germ life than the remainder of the +milk has led some to advocate its rejection when a sanitary milk +supply is under consideration. While from a purely quantitative +point of view, this custom may be considered advantageous, in +practice, however, it is hardly worth while since it is not at all +certain that the rejection will have any effect on the keeping +quality or healthfulness of milk. This is especially true if the +ends of the teats are thoroughly cleaned before milking. It is true +that the fore-milk is relatively deficient in fat so that the loss +of butter fat occasioned by the rejection of the first few streams +is comparatively slight. + +=Contamination from utensils.= One of the most important phases of +contamination is that which comes from the utensils used to hold the +milk from the time it is drawn until it is utilized. Not only is +this important because it is a leading factor in the infection of +milk, but because much improvement can be secured with but little +trouble, and it is especially necessary that the dairy student +should be made familiar with the various conditions that obtain. +Pails and cans used to hold milk may be apparently clean to the eye, +and yet contribute materially to the germ content of the milk placed +in them. Not only does much depend upon their condition, but it is +equally important to take into consideration their manner of +construction. Dairy utensils should be simple in construction, +rather than complex. They should be made so that they can be readily +and easily cleaned, or otherwise the cleaning process is apt to be +neglected. + +Of first importance are those utensils that are used to collect the +milk and in which it is handled while on the farm. The warm milk is +first received in pails, and unless these are scrupulously cleaned, +an important initial contamination then occurs. As ordinarily +washed, the process falls far short of ridding the utensils of the +bacterial life that is adherent to the inner surface of the pail. +Then, too, all angles or crevices afford an excellent hiding place +for bacteria, and it is very important to see that all seams are +well soldered. Round corners and angles flushed with solder greatly +facilitate thorough cleaning of utensils. Tin utensils are +recognized as most satisfactory. + +Shipping cans are likely to serve as greater infecting agents than +pails for they are subject to more wear and tear and are harder to +clean. As long as the surface is bright and smooth, it may be easily +cleaned, but large utensils, such as cans, are likely to become +dented and rusty in spots on the inner side. The storage of milk in +such utensils results in its rapid deterioration. The action of +rennet has been found to be greatly retarded where milk comes in +contact with a rusty iron surface. It is also probable that some of +the abnormal flavors in butter are due to the action of acid cream +on iron or copper surfaces from which the tin has been worn. It is +equally important that attention be paid to the care of strainers, +coolers, and the small utensils. Cloth strainers are more or less of +a hotbed for bacterial growth, for unless they are boiled, and then +dried quickly and thoroughly, germ growth will continue apace in +them, as long as they contain any moisture. + +=Milking machines and farm separators.= The introduction of these +special types of dairy machinery in the handling of milk on the farm +has materially complicated the question of the care of milk. Both of +these types of apparatus are much more complicated than the usual +milk utensil; consequently, the danger of imperfect cleaning is +thereby increased. This is still further accentuated by the fact +that cleansing of utensils on the farm can never be done so well as +at the factory or milk depot where steam is available. The milking +machine may be easily kept in a comparatively germ-free condition, +but unless this is done, it contributes its quota of germ life to +the milk. + +The farm separator is more widely used than the milking machine and +in actual practice the grossest carelessness prevails in the matter +of its care. Frequently it is not taken apart and thoroughly +cleansed, but is rinsed out by passing water through the machine. It +is impossible by such a treatment to remove the slime that collects +on the wall of the bowl; the machine remains moist and bacterial +growth can go on. Such a machine represents a most important source +of contamination of milk and cream and it is probable that the +widespread introduction of the hand separator has contributed more +to lower the quality of cream delivered at the factory than any +other single factor. + +=Contamination from factory by-products.= The custom of returning +factory by-products in the same set of cans that is used to bring +fresh milk is a prominent cause of bad milk. Whey and skim milk are +rich in bacterial life, and not infrequently are so handled as to +become a foul, fermenting mass. If the cans used to transport this +material are not scrupulously cleaned on the farm, transfer of +harmful bacteria to the milk is made possible. In this way the +carelessness of a single patron may be the means of seeding the +whole factory supply. This custom is not only liable to produce a +poor quality of milk, but it is more or less of a menace to all the +patrons of a factory, inasmuch as the opportunity always obtains +that disease-producing organisms may thus be introduced into the +supply. Not infrequently is tuberculosis thus spread through the +medium of factory by-products. + +[Illustration: Fig. 8.--Whey Disposal. + +Whey barrels at a Wisconsin Swiss cheese factory. Each patron's +share is placed in a barrel which is so situated that it is +impossible to empty it completely; thus it is not cleaned during the +season.] + +The manufacture of Swiss cheese presents a striking example of the +disregard which factory operators show toward the employment of +bacteriological principles. In these factories, the custom is widely +practiced of apportioning the patrons' allotment of whey into +individual barrels which are supposed to be emptied each day. As +these barrels are, however, rarely ever cleaned from the beginning +to the end of the season, they become very foul, and the whey placed +in them from day to day highly polluted. It is this material which +is taken back to the farms in the same set of cans that is used for +the fresh milk. When one recalls that the very best type of milk is +essential for the making of a prime quality of Swiss cheese, and +that to secure such, the maker insists that the patron bring the +product to the factory twice daily, the before mentioned practice +appears somewhat inconsistent. + +=Treatment of factory by-products.= To overcome the danger of +infecting milk from factory by-products with either undesirable +fermentative organisms, or disease-producing bacteria, the most +feasible process is to destroy these organisms by the application of +heat. In Denmark, some portions of Germany, and in some of the +states in this country, laws exist which require the heating of all +skim milk before it is returned to the farm. This is done by the +direct use of exhaust steam, or running the product through heaters. + +The treatment of whey in cheese factory practice is especially +important since the warm whey must be stored for a number of hours +before it is returned to the farms. Even under the best of +conditions the whey is certain to be in an advanced state of +fermentation when placed in the milk cans, and it only needs the +infection of the whey tank with harmful bacteria to cause great loss +on account of the injury of the product by these bacteria. Among +Canadian factories the custom of heating the whey as it passes from +the cheese vat to whey tank has been introduced, and where ever +adopted has been retained, because, it has resulted in such an +improvement of the cheese that the gain was much greater than the +cost, which is estimated at not over fifty cents per ton of cheese. +The whey is heated not to exceed 155° F.; the hot whey serves to +scald the whey tank and as the mass of whey is usually quite large, +it does not cool to a point where bacterial growth can take place +for a number of hours. The whey is thus quite sweet when returned to +the farm and has greater feeding value. The heating also prevents +the creaming of the whey in the tank and thus avoids the soiling of +the cans with grease which is most difficult to remove. + +Where compulsory legislation is in force it is generally required +that these by-products be heated to a temperature of at least 176° +F. This is done so as to destroy effectually the organisms of +tuberculosis, and especially to permit of the utilization of the +so-called Storch test,[1] which enables a person to determine +quickly whether milk or whey has been heated or not. + + [1] Storch (40 Rept. Expt. Stat., Copenhagen, 1898) has devised + a test whereby it can be determined whether this treatment has + been carried out or not; milk contains a soluble enzyme known as + peroxidase which has the property of decomposing hydrogen + peroxid. If milk is heated to 176° F., (80° C.) or above, this + enzyme is destroyed, so that the above reaction no longer takes + place. If potassium iodide and starch are added to unheated milk + and the same treated with hydrogen peroxid, the decomposition of + the latter agent releases oxygen which acts on the potassium + salt, which in turn gives off free iodine that turns the starch + blue. + +=Cleaning utensils.= Various processes are applied to dairy utensils +to cleanse them. In removing visible dirt and foreign matter, much +of the bacterial life is mechanically eliminated, but most of the +cleaning processes fail to destroy the germ life in these utensils. + +In rinsing, washing, or even scalding, the water is not applied at a +sufficiently high temperature to destroy effectively the bacteria. +These processes are primarily used for the removal of dirt and other +matter. To facilitate such removal, washing powders of various kinds +are frequently employed; some of these possess considerable +disinfecting action. All utensils after cleansing should be +thoroughly rinsed in clean, hot water. Even where no further +treatment is given, a careful cleaning may so reduce the germ +content on the inner surface of utensil as to render contamination +therefrom relatively unimportant. Most of the contamination in a +well cleaned utensil comes from the cracks and angles, which permit +of the collection of the dirt. If these are properly attended to, +thorough cleaning and rinsing alone will accomplish much. + +To exert an actual germ-destroying effect on the bacterial content +of the utensil, resort must be had to boiling or steaming. To treat +utensils so as to render them wholly germ-free would be impractical +under ordinary commercial conditions, as it would consume too much +time, although with proper apparatus, this process is not +impossible, but it is well within the limits of practicability in +factory treatment to apply steam for a short period of time. Where +cans, pails and such utensils, are steamed for a minute or so after +being thoroughly cleaned, the germ content is greatly reduced. In a +series of tests by Harrison, the germ content of a set of cans +cleaned in an ordinary way was 442,000 bacteria per cubic centimeter +in 100 cubic centimeters of wash water; in a set washed in tepid +water and then scalded--the best farm practice--it was 54,000 per +cubic centimeter, while in cans carefully washed and then steamed +for 5 minutes, it was reduced to 880 per cubic centimeter. It would +not be worth while to institute measures that would accomplish the +destruction of this small residual content. + +The use of steam, therefore, is of great service in eliminating +bacterial life in all utensils. In apparatus of at all complicated +design, it is absolutely necessary. Of course, ordinarily, steam can +be applied only at the factory, as the farm does not usually afford +facilities for its easy generation. This fact has led in some cases +to the adoption of the method of cleaning and sterilizing the cans +at the factory rather than to await their arrival at the farm. This +custom is most frequently followed in milk supply plants. + +It is also very important in cleaning dairy utensils to see that +they are rapidly and thoroughly dried after being washed and +steamed. As pointed out above, the short period of steaming that can +be followed in practice does not kill all the bacteria. If moisture +is retained, conditions permit of the growth of the undestroyed +organisms. Tests made on glass milk bottles showed that considerable +growth occurred in the condensation water even after quite thorough +sterilization. Some of the devices used for the sterilization of +such utensils as milk cans are so arranged that, after steam has +been introduced, hot air is passed into the can until it is +thoroughly dried. Other utensils such as cloth strainers become +sources of contamination unless the articles are thoroughly and +quickly dried after cleaning. + +In a general way, it may be said that whenever a utensil is so +constructed and in such a condition that every portion of its +surface can be reached by a cloth or a brush, it can be kept in a +sanitary condition. But whenever any portion cannot be thus reached, +whether it is an angle or a seam in a pail or can, the interior of +the separator bowl, or in the pipes used for conducting milk, +contamination is certain to result from such places, unless extreme +care is taken to destroy the bacteria therein by steaming. + +=Contamination from the animal.= In the process of milking, the +bacterial content of the milk is materially increased. In part this +comes from the utensils into which the milk is drawn, but the animal +herself, the milker, as well as the surrounding air, also contribute +to a varying extent. Of these factors, the one fraught by far with +the most consequence, is the influence of the animal herself. It is +a popular belief that the organisms found in milk are derived from +the feed and water which the animal consumes, but under normal +conditions, the bacteria consumed in food pass through the +intestinal canal and do not appear in the circulation. It must not +be assumed, however, that the character of feed and water supply is +of no moment. Stock should be given pure and wholesome water and no +decomposed or spoiled food should be used. + +The infection traceable directly to the cow is modified materially +by the conditions under which the animal is kept and the character +of the feed consumed. The nature of the fecal matter is in part +dependent upon the character of the food. The more nitrogenous the +ration fed, the softer are the fecal discharges, producing a +condition which is more likely to soil the coat of the animal unless +care is taken. The same is true with animals kept on pasture in +comparison with those fed dry fodder. + +Stall-fed animals, however, are more likely to have their flanks +fouled, unless special attention is paid to the removal of the +manure. All dairy stalls should be provided with a manure drop which +should be cleaned as frequently as circumstances will permit. + +[Illustration: Fig. 9.--Bacteria on Hairs. + +Each colony on the hair represents one or more bacteria that were +adherent to the hair when it was placed on the surface of the solid +culture-medium.] + +The animal contributes materially to the quota of germ life finding +its way into the milk through the dislodgment of dust and filth +particles adhering to its hairy coat. The nature of this coat is +such as to favor the retention of these particles. Unless care is +taken, the flanks and udder become polluted with fecal matter, which +upon drying is displaced with every movement of the animal. Every +hair or dirt particle so dislodged and finding its way into the +milk-pail adds its quota of organisms to the liquid. This can be +readily demonstrated by placing cow's hairs on the moist surface +of gelatin culture plates. Almost invariably bacteria will be found +in considerable numbers adhering to such hairs, as is indicated in +Fig. 9. + +Dirt particles are even richer in germ life. Not only is there the +dislodgment of hairs, epithelial scales, and masses of dirt and +filth, but during the milking process, as at all other times, every +motion of the animal is accompanied by a shower of _invisible_ +particles, more or less teeming with bacterial life. All of this +material contains organisms that are more or less undesirable in +milk. Bacteria concerned in gassy fermentations and those capable of +producing obnoxious taints are particularly common, so that this +type of pollution is especially undesirable in milk. + +=Amount of dirt in milk.= When one remembers that the larger part of +fresh manure is of such a nature that it does not appear as +sediment, the presence of evident filth in milk must bespeak +careless methods of handling. + +The sediment or dirt test is used quite extensively to ascertain the +amount of dirt milk may contain. By means of a cotton filter, the +insoluble residue is removed and is made evident upon a layer of +absorbent cotton. Milk that would show with difficulty any evidence +of dirt upon ordinary examination reveals such defects very readily +in this test. + +=Exclusion of dirt.= It is better to keep bacteria out of milk, so far +as practicable, rather than to attempt to remove them after they +have once gained entrance. As is usual, prevention of trouble is +much more easily accomplished than removing the difficulty after it +once occurs. + +[Illustration: Fig. 10.--Dirt from Milk. + +The dirt adherent to each of the filters was obtained from one pint +of milk. The milks tested were produced on different farms.] + +Much reduction as to the amount of dirt that finds its way into milk +may be accomplished by improved stable environment. The fouling of +the udder and flanks comes from wading in dirty water, muddy yards, +and from improper type of stalls. Barnyards are often a disgrace +through the accumulation of manure and seepage. Cows wading in such +mire cannot but accumulate mud and filth to a material degree on the +teats and udder. Greater care as to drainage of the barnyard and the +paving of same with gravel, cinders, etc., will permit of its being +kept clean, and so prevent the fouling of animals. But more +important than the yard is the stall which the animal occupies in +the stable. The essential feature is to have a stall of such +construction as to keep the animal out of her own manure when she +lies down. To accomplish this, it is necessary to have a manure drop +behind the stall proper so that the feces and urine are kept out of +the bed of the stall as much as possible. + +[Illustration: Fig. 11.--The Model Stall. + +A stall of this type keeps the animals clean, and thus aids greatly +in producing good milk.] + +Most of the stalls widely advertised in the farm press seek to +accomplish this in one way or another, usually by some arrangement +by which the cow is forced back when standing and drawn forward on +lying down. In Fig. 11 a type of stall is illustrated that +accomplishes this most successfully; the essential feature being a +2×3-inch wood strip nailed to the stall floor immediately in front +of the hind feet of the animal when in a standing position. When the +animal lies down, she crowds forward to avoid lying on this strip, +and thus is out of contact with the manure, except such as is +carried onto the bedding by the hind feet. By the use of this stall +it is possible to keep the animals free from all accumulations of +manure. + +Effort should be made to prevent fouling of the animals rather than +in cleaning them after once soiled. It is very evident that where +the cattle come to the milker with muddy udders, they will not be so +cleaned before milking as to prevent a large amount of such dirt +from entering the milk. However, when all that can be done towards +keeping the cows clean has been accomplished, a small amount of +grooming will greatly reduce the contamination coming from them. + +The kind of bedding used in the stalls may have a marked influence +on the contamination coming from the animal. If the straw is dusty, +partially rotten and moldy, the bacteria and molds adhere to the +coat of the animal and are thus introduced into the milk. In the +case of cattle on pasture, no visible evidences of dirt are usually +present but the hair is covered with the dust coming from the soil. +There is very good reason to believe that the quality of milk is +influenced by the type of pasture on which the cows graze, due to +the difference in the types of bacteria in the surface soil. The +milk from animals on low land is more likely to show undesirable +fermentations than that from those grazing on higher lands. This is +not due to the influence of the feed as is often supposed but rather +to the dirt from the coat of the animal. + +=Washing the udder.= If a surface is moist, dust and the adherent +bacteria cannot be easily dislodged. The air over snow-covered +mountains or over oceans is relatively free from bacteria. The udder +and flanks of the animals can be carded to remove the loose hairs +and the evident dirt; the fine dust can now be removed by wiping +with a clean damp cloth just before the milking process. The actual +washing and wiping of the udder and flanks still further reduces the +contamination coming from the animal; experiments show a reduction +of fully three-fourths of total contamination. Clipping the udder +and flanks also aids in keeping the animal clean. + +It is often asserted that the treatment of the animals in these ways +reduces the yield of milk. It is certain that such an effect will +persist for only a short time and there is reason to believe that +grooming increases the yield. + +[Illustration: Fig. 12.--Sanitary Milk Pails. + +The small opening is very efficient in keeping the dirt out of +milk.] + +=Sanitary milk pails.= The entrance of organisms into the milk can be +greatly reduced by lessening the area of the milk pail exposed to +the dust shower. To accomplish this purpose a number of so-called +sanitary or hygienic milk pails have been devised. In some cases, +these are the regular type of pail provided with a cover having a +small opening through which the milk is received. In other cases, a +strainer is interposed so as to remove more effectually the coarse +particles. While pails of this type are successful in the removal of +a large part of the dirt, and consequently reduce materially the +bacterial content of the milk, yet they must be of simple +construction, so that they can be kept in a clean condition in order +to adapt them for general practical use. The use of such a utensil +increases materially the keeping quality of the milk. + +[Illustration: Fig. 13.--Sanitary Milk Pails. + +The Stadtmueller pail and the Truman pail, two of the most practical +of the small-topped pails.] + +Stocking has shown that under ordinary barn conditions, the use of +small-topped pails reduced the number of bacteria 95 per cent; with +dirty cows the reduction in bacteria amounted to 97 per cent. A +six-inch opening presents only one-fourth as large an exposure as a +twelve inch, so that the reduction in bacterial content is greater +than the lessening in the size of the openings of the pails. The +ordinary pail receives dust not only from the udder, but also from +the flank which is usually a more important source of contamination +than the udder itself, while the small-topped pail receives only +that from the udder. + +[Illustration: Fig. 14.--use of Sanitary Milk Pails. + +The open pail is fully exposed to the falling dust while the hooded +pail excludes much of the dust and dirt coming from the animal.] + +=Milking machines.= Where the milk is removed from the udder by +machine methods, instead of by hand, it is possible to eliminate +nearly all external contamination from the animal and her +surroundings. The only opportunity for infection is then through the +leakage of air around the teat cups. Care should be taken to see +that the teats are in a clean condition before applying the suction +cups. The main problem in the use of a milking machine is to keep +the apparatus in an aseptic condition. Immersion of the teat cups +and the rubber connections in lime water, brine solution, or other +mild antiseptics, prevents bacterial development. Hastings has found +that milk having a germ content of less than 10,000 bacteria per +cubic centimeter may be produced by the use of a properly handled +milking machine. + +=Contamination from the milker.= While the milker is a small factor in +comparison with the animal in the matter of contamination, yet he +can not be neglected, as it is within his power to affect profoundly +the quality of the milk. His personal habits as to cleanliness and +his appreciation of the precautions necessary in the production of +clean milk have much to do with the contamination of the milk. The +milking should be done with dry hands, although a little vaseline +may be used with effect. The hands should be washed before milking +as milk is certain to come in contact with them to some extent. The +milking should be done with the whole hand rather than stripping +between the thumb and finger; the clothing should be covered with +clean overalls and jumper, or at least a clean apron should be worn +during the milking. If these are of white material, more frequent +laundering is likely to result. + +=Contamination from air.= It is difficult to disassociate the +contamination arising from the condition of the air from that +derived directly from the animal. Barn operations of various kinds +result in the production of dust, particularly where dry forage, +such as hay or straw, is handled. Where manure is given an +opportunity to dry, dust is readily produced, and such material is +particularly replete with bacterial life. Some kinds of dust, such +as that originating from ground grains, or shavings that may be used +for bedding, contain a small amount of bacterial life in comparison +with the dust from hay, or other dry fodder. In a dried condition, +the slightest movement is apt to dislodge these fine particles, and +they float in the air for considerable periods of time. If milk is +drawn and exposed to the air of the barn during the feeding +operations, it is subject to the dust shower that is present. Where +the storage can is allowed to stand in the stable during the +milking, even though it is covered with a strainer, this +accumulation of microscopic particles is added to the milk, as they +readily pass the meshes of the finest strainer. + +[Illustration: Fig. 15.--contamination From the Air. + +This culture plate, three inches in diameter, was exposed for 30 +seconds in the barn during feeding of dry fodder. A 12-inch pail +exposes over 18 times the surface of this plate.] + +=Removal of dirt after introduction.= The more primitive method of +improving the quality of milk, so far as its dirt content is +concerned, is to attempt to remove the grosser particles of +contamination after entrance. In the case of straining, the method +is usually applied at the time of milking, but in the case of +filtering and clarifying, it is carried out at the milk station, in +an effort to improve the appearance of milk and overcome the +influence of careless methods of the producer. By the use of +strainers, either metallic or cloth, it is possible to remove +particles of hair, undissolved dirt and manure, but it must be +remembered that these grosser _visible_ particles of pollution are +not really the cause of the troubles which may ensue in improperly +handled milk. The bacteria which are adherent to these foreign +particles are in large measure washed off in the process of +straining, and pass through the meshes of the finest strainer. The +main service, therefore, of straining is to improve the appearance +of the milk, and it has no effect on the quality in any way. + +=Production of clean milk.= The problem of clean milk is important, +whatever may be the use to which milk may be put. It is important in +the manufacture of butter, but owing to the fact that the fat is not +readily acted upon by bacteria, it is not so sensitive to bacterial +conditions, as when the milk is made into cheese. In this product, +the bacterial condition of the milk is a matter of prime importance. +In milk destined for direct consumption, the exclusion of the +bacteria becomes yet more important. While it is impossible to +exclude bacteria so completely that milk will not undergo +fermentative changes, yet for domestic consumption it is preferable +to have milk with as low bacterial content as can readily be +secured. The highest type of market milk, that known as sanitary, or +certified, is produced under such extreme conditions of care as to +contain the minimum germ content. To accomplish these results +requires such stringent control as to increase greatly the cost of +the product. Pure, clean milk can be produced at a very slight +increase in cost over the regular expense of milk production, if the +right kind of attention is given to certain details of a practical +character. Improvement in our milk supplies must largely come from +this source, for any improvement to be permanent must be made to +pay, and it requires considerable education to secure the +co-operation of consumers and their willingness to pay for any +material increase in the quality of the product. + +In the foregoing factors concerned in the contamination of milk, it +is of course impossible to measure accurately the influence of the +different sources of infection, as these are continually subject to +variation in every case. As a rule, the most important factors are +those pertaining to the utensils and the condition of the animal +herself. If these two factors are brought under reasonable control, +the major portion of contamination that ordinarily obtains is done +away with. The application of the remedial or preventive measures +heretofore mentioned will greatly reduce the germ content of the +milk. + +=Cooling of milk on farm.= Bacterial growth is directly related to +temperature conditions, and with summer temperatures, such +development goes on apace, unless it is checked by early cooling. +The larger portion of bacteria that find their way into milk, +especially those that are previously in contact with the air, are in +a dormant condition, and are therefore not stimulated into immediate +growth, unless reasonably high temperatures prevail. In milk, which +comes from the animal at blood heat, this growth is greatly +stimulated. To counteract this effect, milk should be chilled as +soon after milking as possible. If the temperature is immediately +lowered to 50° F., or lower, actual cell development is greatly +retarded, and the rate of souring, and other fermentative changes +thereby diminished. In this country ice is liberally used in +accomplishing this result. In Europe, the use of ice is much less +common. The employment of such artificial means of refrigeration +makes possible the shipment of milk for long distances by rail. New +York city now receives milk that is produced in Canada and +northeastern Ohio. + +[Illustration: Fig. 16.--Effect of Cooling Milk.] + +=Aeration of milk=. The custom has been extensively recommended of +subjecting milk to the influence of air in the belief that such +exposure permits of the interchange of gases that would improve the +quality. In practice, this process, known as aeration, is carried on +in different ways. In some cases, air is forced into the milk; in +others, the milk is allowed to distribute itself in a thin sheet +over a broad surface, falling in drops or tiny streams through the +air. Whenever this process is carried on at a temperature lower +than that of the milk, it results in more or less rapid cooling. + +In earlier times, aeration was generally recommended and practiced, +especially in connection with the cheese industry, but carefully +controlled experiments fail to show that the process exerts any +material influence on the rate of germ development. If it is carried +out in an atmosphere more or less charged with bacteria, as in the +barn or stable, it is more than likely to add to the bacterial +content of the milk. While to some extent odors may be eliminated by +the process, the custom is not followed so generally now as it used +to be some years ago. + +=Absorption of taints.= A tainted condition in milk may result from +the development of bacteria, acting upon various constituents of the +milk, and transforming these in such a way, as to produce +by-products that impair the flavor or appearance of the liquid; or +it may be produced by the milk being brought in contact with any +odoriferous or aromatic substance, under conditions that permit of +the direct absorption of such odors. + +This latter class of taints is entirely independent of bacterial +action, and is largely attributable to the physical property which +milk possesses of absorbing volatile odors. This direct absorption +may occur before the milk is withdrawn from the animal, or +afterwards if exposed to strong odors. + +It is not uncommon for the milk of animals advanced in lactation to +have a more or less strongly marked odor and taste; sometimes it is +apt to be bitter, at other times salty to the taste. It is a defect +that is peculiar to individual animals, and is liable to recur at +approximately the same period in lactation. The peculiar "cowy" or +"animal odor" of fresh milk is an inherent peculiarity that is due +to the direct absorption of volatile elements from the animal +herself. + +Many kinds of feed consumed by the animal produce a more or less +pronounced taint or flavor in the milk. With some plants, such as +garlic, leeks, turnips, and cabbage, the odor is so pronounced as to +render the milk quite unfit for use. In some states along the +Atlantic seaboard, wild plants of this character in woodland +pastures may be so abundant as to make it impossible to pasture +milch animals. The difficulty in such cases is due to absorption of +the volatile principles into the circulation of the animal, and if +such feed is consumed shortly before milking, the characteristic +odors appear in the milk. If consumed immediately after the milk is +withdrawn from the animal, sufficient time may elapse so that the +peculiar odors are dissipated before the milk is again secreted. The +same principle applies in a lesser degree to the use of certain +green fodders that are more suitable for feed, such as rape, green +rye, or even silage. Silage produces a distinct, but not unpleasant +odor in milk, but newly pastured rye often confers so strong an odor +as to render the milk unusable. + +Where certain drugs are employed in the treatment of animals, such +as belladonna, castor oil, sulfur, or turpentine, the peculiar odors +may reappear in the milk. Such mineral poisons as arsenic have been +known to persist for a period of three weeks before elimination. + +On account of the elimination of many drugs, unchanged, from the +animal in the milk, the milk of any animal that is receiving +medicine should not be used for human food. When such milk is mixed +with that of a number of other animals and when it is used by +adults, no harm is likely to result, but when the dilution is not +great and the milk is used for young children it may affect them +through its content of the drug. The feed may not only affect the +quality of milk but its value as food. One of the most prominent of +American dairymen, who has for many years produced milk especially +for children's use, has said that he could feed his cows so as to +make ill every child receiving the milk. + +=Absorption of odors after milking.= If milk is brought in contact +with strong odors after being drawn from the animal, it will absorb +them readily, as in the barn, where frequently it is exposed to the +odor of manure and other fermenting organic matter. + +It has long been a popular belief that milk evolves odors and cannot +absorb them so long as it is warmer than the surrounding air, but +from experiments of one of us (R), it has been definitely shown that +the direct absorption of odors takes place much more rapidly when +the milk is warm than when cold, although under either condition, it +absorbs volatile substances quite rapidly. + +The custom of straining the milk in the barn has long been +deprecated as inconsistent with proper dairy practice, and in the +light of the above experiments, an additional reason is evident why +this should not be done. + +Even after milk is thoroughly cooled, it may absorb odors, as is +noted where the same is stored in a refrigerator with certain +fruits, meats, fish, etc. + +=Distinguishing bacterial from other taints.= In perfectly fresh milk +it is relatively easy to distinguish between taints caused by the +growth of bacteria and those attributable to direct absorption. If +the taint is evident at time of milking, it is in all probability +due to character of feed consumed, or possibly to medicines. If, +however, the intensity of the taint grows more pronounced as the +milk becomes older, then it is probably due to living organisms +which require a certain period of incubation before their +by-products are most evident. + +Moreover, if the difficulty is of bacterial origin, it can be +frequently produced in another lot of milk (heated or sterilized is +preferable) by inoculating the same with some of the original milk. +Not all abnormal fermentations are able, though, to compete with the +lactic acid bacteria, and hence outbreaks of this sort soon die out +by the re-establishment of more normal conditions. + +=Factory contamination.= As the time element is of importance in the +production of troubles due to bacteria, it follows that infection of +milk on the farm is fraught with more consequence than factory +contamination, as the organisms introduced would have a longer +period of development. Nevertheless, the conditions in the factory +are by no means to be ignored, as they not infrequently permit the +milk to become seeded with highly undesirable types. A much more +rigid control can be exercised in the factory, where steam is at +hand as an aid in the destruction of organisms. In the cleaning of +pumps and pipes, steam is absolutely necessary to keep such +apparatus in a sanitary condition. + +The water supply of the factory is a matter of prime importance, as +water is used so extensively in all factory operations. When taken +from a shallow well, especially if surface drainage from the +factory is possible, the water may be contaminated to such an extent +as to introduce undesirable bacteria in such numbers that the normal +course of fermentation may be changed. The quality of the water, +aside from flavor, can best be determined by making a curd test (p. +99) which is done by adding some of the water to boiled milk, and +incubating the same. If "gassy" fermentations occur, it signifies an +abnormal condition. In deep wells, pumped as thoroughly as is +generally the case with factory wells, the germ content should be +very low, ranging from a few score to a few hundred bacteria per +cubic centimeter at most. The danger from ice is much less, for the +reason that good daily practice does not sanction using ice directly +in contact with milk or cream. Then, too, water is largely purified +in the process of freezing, although if secured from a polluted +source, reliance should not be placed in this method of +purification, for even freezing does not destroy all vegetating +bacteria. + +The ordinary house fly is an important source of contamination in +creameries, cheese factories and city milk plants. They are of +importance not only in increasing the number of fermentative +bacteria in milk but they may serve to contaminate it with +disease-producing organisms. The windows of all places where milk is +handled, whether on the farm or elsewhere should be screened. + +It should be kept in mind in the handling of milk and other dairy +products that human food is being prepared and that cleanliness is +desirable from every point of view, and that the methods of +handling and production should compare with those used in the +preparation of foods which like milk cannot be cleaned when once +polluted. Desirability, keeping quality, healthfulness and the value +of every product made from milk depends upon the extent and amount +of contamination. + + + + +CHAPTER IV. + +INFECTION OF MILK WITH PATHOGENIC BACTERIA. + + +That the disease-producing, or pathogenic bacteria, are able to +infect milk supplies is shown by the fact that numerous epidemics of +contagious disease have been directly traced to milk infection. Milk +is generally consumed in a raw state, and as a considerable number +of this class of organisms are able not only to live but actually +grow in milk, which is such an ideal culture-medium for the +development of most bacteria, it is not surprising that disease +processes should be traced to this source. The organisms in milk +capable of causing disease do not alter or change its physical +properties sufficiently to enable their presence to be detected by a +physical examination. + +=Origin of pathogenic bacteria in milk.= Disease-producing bacteria +may be grouped, with reference to their relation toward milk, into +two classes, depending upon the manner in which infection occurs: + +Class I. Disease-producing bacteria capable of being transmitted +directly from a diseased animal to man through the medium of +infected milk. + +Class II. Bacteria pathogenic for man but not for cattle, which are +capable of thriving in milk after it is drawn from the animal. + +In the first group, the disease produced by the specific organism +must be common to both cattle and man. The organism must live a +parasitic life in the animal, developing in the udder, and so infect +the udder. It may, of course, happen that diseases toward which +domestic animals alone are susceptible may be spread from one animal +to another in this way without affecting human beings. + +In the second group the bacterial species live a saprophytic +existence, growing in milk, as in any other nutrient medium, if it +happens to find its way therein. In such cases, milk indirectly +serves as an agent in the dissemination of disease, by giving +conditions favorable to the growth of the disease germ. + +By far the most important of diseases that may be transmitted +directly from animal to man through a milk supply is tuberculosis, +but in addition to this, foot and mouth disease (aphthous fever in +children), Malta fever, and acute enteric troubles have also been +traced to a similar source of infection. + +The most important specific diseases that are disseminated through +subsequent infection of the milk are typhoid fever, diphtheria, +scarlet fever, and cholera, but, of course, the possibility exists +that any disease germ capable of living and thriving in milk may be +spread in this way. In addition to these diseases that are caused by +the introduction of specific organisms (the causal organism of +scarlet fever has not yet been definitely determined), there are a +large number of more or less illy defined troubles of an intestinal +character that occur especially in infants and young children that +are undoubtedly attributable to the activity of micro-organisms that +gain access to milk during and subsequent to the milking, and which +produce changes in milk before or after its ingestion that result +in the formation of toxic products. + +=Tuberculosis.= This disease is by far the most important bacterial +malady that affects man and beast. In man, it assumes a wide variety +of phases, ranging from consumption, tuberculosis of the lungs, +which is by far the most common type, to scrofulous glands in the +neck, cold abscesses, hip-joint, and bone diseases, as well as +affection of the bowels. These various manifestations are all +produced by the inroads of the specific organism, Bacillus +tuberculosis. The bovine, as well as swine, fowls, and other +warm-blooded animals, are also affected with similar diseases. In +man, the importance of the malady is recognized when it appears that +fully one-seventh of the human race die of this scourge. In cattle, +the disease is equally widespread, particularly in those countries +where live stock has been intensively developed. In the northern +countries of Europe, such as Denmark, Germany, England, France, and +the Netherlands, as well as in Canada, and this country, this +disease has been most widely disseminated. This has been occasioned, +in large measure, because of the exceedingly insidious nature of the +disease in cattle, thereby permitting interchange of such diseased +stock without the disease being recognized. Tuberculosis is found +more abundantly in this country in dairy than in beef stock. Dairy +cattle are, however, not more susceptible, but the closer +environment in which milch cattle are kept, and the fact that there +has been greater activity in the matter of introducing improved +strains, accounts for the larger percentage of affected animals. + +It has been a disputed question for some years whether the organisms +producing bovine and human tuberculosis are identical or from the +practical standpoint, whether the bovine type of disease is +transmitted under natural conditions to man. The bacteriologist can +readily detect differences in appearance, in growth of cultures, and +in disease-producing properties between the two strains. Of the two, +the bovine is much the more virulent when inoculated into +experimental animals. In a considerable number of cases, record of +accidental infection from cattle to man has been observed. These +have occurred in persons making postmortem examination on +tuberculous animals, and the tubercular nature of the wound proven +by excision and inoculation. + +More recently, since the agitation by Robert Koch of Germany, a +number of scientific commissions have studied particularly the +problem of transmission. It is now estimated that perhaps seven per +cent of the tuberculosis in man is of bovine origin. This is almost +wholly confined to children. The portions of the body that become +diseased, when the infection has resulted from the use of milk, are +the glands of the neck and of the abdomen. + +=Manner of infection in man.= In the main, the source of the malady +may be traced either to air infection or to the food, if one +disregards the comparatively small number of cases of wound +infection. Air is frequently a medium by which the germ is +transferred from one person to another. The sputum is exceedingly +rich in tubercle bacilli and since this material is carelessly +distributed by tubercular people, the air of the cities, villages +and public buildings will frequently contain tubercle organisms. +Some of the organisms in the air find their way into the lungs, +there to develop and produce consumption. The organisms in the air +may be deposited in the nasal passages and throat, and ultimately +find their way into the tissues of the body by penetrating the walls +of the throat or of the intestine. It is probable that the tubercle +bacilli thus introduced may find their way to the lungs and there +develop without leaving any trace of their path. + +Food may also possibly serve as a medium of infection. The +contamination of solid food from flies and other sources is, of +course, a possibility, but tuberculous meat from cattle and swine is +much more likely to occur, although it must be said that the +processes of preparing such food for use (roasting, frying, and +boiling) are sufficient to destroy the vitality of the causal +organism. The fact that most food products of this character are now +inspected renders this possibility less likely to occur. + +Unquestionably, the likelihood of ingesting tubercle organisms is +much greater with milk than with any other food supply, as milk is +consumed usually in an uncooked state, and as microscopic and +physiologic tests indicate that not infrequently milk from +tuberculous animals contains these organisms. + +=Distribution of the disease in animals.= As practically any organ of +the body may be affected with tuberculosis, it naturally follows +that the lesions of this disease are widely distributed. The disease +germ is introduced, in the main, through the lymph and not the blood +system; consequently, in the initial stages the evidence of +tuberculosis is often comparatively slight, and the lesion is +restricted in its development. Where such a condition obtains, it is +known as "closed," in contradistinction to "open" tuberculosis, +where the diseased tissue is more or less broken down and is +discharging into the circulation, or elsewhere. Manifestly, the +danger of spreading not only in the affected animal itself, but to +the outside, is much greater in the case of the open lesion. +Especially is this true where the disease is present in the lungs or +organs that have an exterior opening so that the material containing +the organisms is discharged from the body in the sputum, manure, +urine or milk. The intestines themselves are rarely affected, but +the lymph glands associated with the intestinal tract are not +infrequently involved. + +=Infection of milk with tubercle bacilli.= In a small percentage of +cases, the udder itself becomes involved. Where this condition +obtains, one or more hard lumps are formed, which slowly increase in +size, usually being restricted to one quarter of the udder. +Sometimes the affected quarter may develop to an enormous size, +producing a hard, painless tumor. Not often does the affected tissue +break down into pus; consequently, no abnormal appearance is to be +noted in the milk secretion until the disease has made very extended +progress, in which case the percentage of fat generally diminishes. +Whenever the udder shows physical manifestation of this disease, the +milk almost invariably is rich in tubercle bacilli. + +Tubercle organisms may also appear in milk of animals in which no +physical symptoms of the disease are to be found. This fact has been +demonstrated by microscopic and animal experiments, but it is also +abundantly confirmed by the frequent contraction of the disease by +calves and hogs when fed on factory by-products. This latter class +of animals is particularly dangerous, because there is no way in +which the danger can be recognized. + +[Illustration: Fig. 17.--a Tuberculous Animal. + +The animal appears perfectly healthy although she has had the +disease for five years.] + +It has also been proven that milk may become infected through the +feces. In coughing up material from the lungs and associated glands, +the matter is swallowed, instead of expectorated, as in man. The +organisms retain their vitality in the intestine, and are voided in +the feces. Under ordinary conditions, the flanks and udder become +more or less polluted with such filth, and the evidence is +conclusive that infection of milk is not infrequently occasioned in +this way. The fact that hogs following tuberculous steers in the +feeding lots are very likely to acquire the disease is explained by +the presence of tubercle organisms in the manure of such animals. + +[Illustration: Fig. 18.--a Tuberculous Animal. + +The last stages of generalized tuberculosis. Note the emaciated +condition.] + +It must be kept in mind that many animals may be infected with +tubercle bacilli and therefore have tuberculosis in the incipient +stages, without their being able to disseminate the disease to +others. In the early stages, they are bacillus-carriers without +being necessarily dangerous at that particular time, but the +possibility always exists, as the disease develops in the system, +that the trouble may assume a more formidable character, and that +slowly developing chronic lesions may become acute, and "open," in +which case, the affected animal becomes a positive menace to the +herd. As the time when the lesions change from the "closed" to the +"open" type and the animal becomes a source of danger cannot be +determined, the only safe way to do is to exclude the milk of all +tuberculous animals from the general supply, whether for direct +consumption, or for manufacture into dairy products and to look upon +every diseased animal as a menace to the herd. This is rendered all +the more necessary when the milk is used for the feeding of +children, who are relatively more susceptible to intestinal +infection than the adult. The early stages of the disease in cattle +are, however, so insidious that no reliance can be placed upon the +detection of the malady by physical means. Fortunately, in the +tuberculin test, a method is at hand, which in a simple, but +effective manner, enables the disease to be distinguished in even +the early stages, long before recognition is possible in any other +way. + +=Tubercle bacilli in dairy products.= When infected milk is used for +the preparation of butter and cheese, the organisms inevitably are +incorporated in them. In the separation of milk a relatively large +part of the tubercle organisms in the milk appear in the cream. In +the making of cheese even more of the organisms are held in the +curd. In butter and cheese, as in milk, no growth of the organism +can take place; however, the vitality of the organism is retained +for a considerable number of months. It is not believed that these +products are of much importance in the spread of tuberculosis in the +human family, since they are not consumed by children to any extent. +Cream is to be considered as a means of distribution since it is +often used by children. + +=Treatment of tuberculous milk.= It is easily possible to treat milk +or factory by-products so as to render them positively safe. The +process of pasteurization or sterilization is applicable to whole +milk, and when effectively done destroys entirely the vitality of +any tubercle bacilli. In making such exposure, care should be taken +to prevent the formation of the "scalded layer," as the resistance +of the organism toward heat is greatly increased under these +conditions. In a closed receptacle, 140° F. for 15 to 20 minutes has +been found thoroughly effective in destroying this organism. A +momentary exposure at 176° F. is likewise sufficient. This is the +method that is almost universally used in Denmark in the manufacture +of the finest butter. + +In the treatment of factory by-products, heat should also be +employed. In Denmark, compulsory pasteurization at not less than +176° F. is required. This treatment prevents not only the +dissemination of tuberculosis among hogs and young cattle, but is +equally efficacious in preventing the spread of foot and mouth +disease. + +The per cent of tuberculous milch cows varies widely in different +sections of the country, being greatest in the older dairy sections, +and in those supplying milk to the cities, on account of the +constant buying and selling of animals, thus giving more frequent +opportunity of introducing the disease into the herds. Throughout +the country at large, probably less than ten per cent of the cows +are tuberculous, and it is estimated that at least one per cent of +the diseased animals have tuberculous udders. It has been suggested +that the dilution of the milk of such animals with that of healthy +cows would remove a great part of the danger from milk. In the +case where the milk of a large number of herds is mixed, this may be +of some importance, but in no case is it safe to assume that +dilution of the milk of tuberculous cows is any guarantee of safety. + +It has been shown that milk, perfectly normal in appearance, coming +from a tuberculous udder could be diluted a million times and still +produce the disease on inoculation into experimental animals. In the +case of swine, the susceptibility is so great that a single feeding +of infected milk, even in a very dilute condition, causes with +certainty the production of the disease. + +Some observers maintain that the contamination of the milk with the +manure of tuberculous animals is of greater hygienic importance, +than that coming from diseased udders, since the number of animals +having tuberculosis of the lungs and intestines is far greater than +those with diseased udders. + +=Economic aspects of bovine tuberculosis.= Not only is this disease +invested with much importance because of its inter-relation with the +human, but from an economic point of view alone, it is undoubtedly +the greatest scourge that affects the dairyman. Its insidiousness +makes it exceedingly difficult to recognize. The consequence is that +many fine herds become seriously involved before its presence is +recognized. In the main, the disease is introduced into a herd by +purchase, often by buying in pure-bred stock to improve the quality +of the herd. Where the disease has been established in a region for +some time, there is also danger that unheated factory by-products, +as skim milk and whey, may function in its spread. Where such +conditions prevail, the spread of the disease in the creamery +district is exceedingly rapid. When once introduced into a herd, +the disease sooner or later spreads from the originally affected +animal to others in the herd. Close contact, and close confinement +in ill ventilated stables facilitate the spread of the disease, and +sooner or later, other animals acquire the trouble. This may all +occur while all animals appear in a healthy condition. + +The symptoms of the disease in the earlier stages are quite +indefinite. As the disease progresses, the nutritive functions +appear to be disturbed, and sooner or later, the body weight begins +to decline, and finally marked emaciation ensues. Accompanying this +condition, especially when the disease is in the lungs, is a cough, +which is generally aggravated with active exercise. While the +run-down condition permits frequently of the detection of the +disease in the advanced stages, it is wholly impossible with any +accuracy to diagnose the trouble in the incipient stages. It is at +this stage that the tuberculin test comes to the aid of the +stockman. + +_Tuberculin test._ This test is made by the injecting beneath the +skin of the animal a small quantity (about 2 c. c.) of tuberculin, +and noting the temperature of the animal, before and after the +injection. Tuberculin, a product of the growth of the tubercle +bacillus, when injected into the body causes a marked rise in +temperature, in the case of an animal affected with the disease, and +no such elevation in the case of a healthy animal. The process of +preparing tuberculin makes it absolutely free from danger, so far as +liability of producing the disease, or in any way injuring the +animal, is concerned. Fig. 19 shows the temperature range of both +reacting and non-reacting animals. While the test is not +absolutely infallible, it is so far superior to any and all other +methods of diagnosis that it should take precedence over them. + +=Miscellaneous diseases.= There are a number of diseases that affect +both human beings and cattle, the causal organisms of which may be +transmitted through the milk. Foot and mouth disease is one wide +spread in European countries but which has not yet gained a +permanent foothold in this country. The ingestion of the milk, which +always contains the causal organism, produces the disease in both +humans and cattle. In the human the disease is very similar to that +in cattle; it may end in death. Vesicles are produced in the mouth, +on the lips, nose and fingers. The causal organism, which has not +yet been demonstrated, may occur in butter or cheese. It is easily +destroyed by pasteurizing the milk. + +[Illustration: Fig. 19.--Temperature Curves. + +1, the temperature curve of a healthy animal after injection with +tuberculin; 2 and 3, the temperature curves of tuberculous animals +after injection with tuberculin. (After Moore.)] + +Anthrax, actinomycosis (lumpy jaw), rabies, and malta fever are +diseases the organisms of which have been found in the milk of +affected animals. In case of the first three, while the possibility +exists of the infection of human beings by milk, it is improbable +that such infection does normally occur. Malta fever is becoming an +important disease in portions of southern Europe. It is produced in +man by the use of milk of goats suffering from the disease. + +The organism causing contagious abortion in cattle is known to be +present in the milk of the infected animal at the time of its +withdrawal from the udder. It is not probable that the organism is +of any sanitary significance as far as man is concerned. It has been +shown that the organism is able to produce a disease in guinea pigs +on artificial inoculation that is very similar, so far as the +lesions are concerned, to tuberculosis. It is also probable that the +by-products of creameries and cheese factories may serve to spread +the disease from one herd to another. + +Inflammation of the udder (garget) is a frequent trouble in every +herd. It is marked by the swelling of one or more quarters, by the +appearance of fever and changes in the appearance and composition of +the milk. The inflammation may be caused by cold or injury, or by +the invasion of the udder with pus-forming bacteria. In the first +case the trouble is not likely to persist for any length of time, +and does not spread to other members of the herd. The milk may be +more or less stringy, and may show a slimy flocculent sediment. It +cannot be asserted that such milk is harmful to man but it should be +rejected on general sanitary grounds, and because it cannot always +be differentiated from that coming from an udder in which the +inflammation is produced by bacteria. + +Inflammation caused by the invasion of the udder with specific +bacteria is usually of greater severity, the entire gland often +becoming involved. The secretion of milk may cease and the function +of the diseased quarters may never be restored. The milk in the less +severe cases may not be abnormal in appearance, but with increasing +severity, the nature of the milk changes, until it may be a watery +liquid. The milk of any animal suffering from any form of garget +should be rejected, as it may cause trouble, especially in children. +There is some reason to believe that organisms coming from cases of +garget have been responsible for the extensive outbreaks of septic +sore throat that have occurred in some parts of the country. + +The milk of animals suffering from indigestion, diarrhea, abscesses +on any part of the body, as from those which have retained the +afterbirth should be likewise rejected. In short only the milk of +healthy animals should be used for human food; that from any animal +suffering from any disease or which is receiving medical treatment +should not be so used. + +=Typhoid fever=. The most important disease germ, distributed through +the medium of milk, that is unable to produce a diseased condition +in the cow is the organism of typhoid fever. This malady is an +intestinal affliction of man, and the germ causing the same is found +abundantly in the dejecta, both solid and liquid, as well as in the +blood in certain stages of the disease. While the causal organism +does not leave the body through the expired air, it is found +abundantly in both the urine and feces. Therefore, the dejecta, and +any articles that may be soiled with the same become a positive +menace. + +Many different methods of transmitting the contagion exist, such as +water, food infected in various ways, contact with infected persons, +and through the medium of milk. Milk is not so frequently the cause +of dissemination as the other factors, but where milk supplies +become contaminated, epidemics of considerable magnitude are wont to +occur. The danger from milk is also aggravated by the fact that the +typhoid bacillus is capable of withstanding considerable amounts of +acid, and consequently finds, even in raw milk containing the normal +lactic acid bacteria, conditions favorable for its growth. In a +considerable percentage of cases, the disease is not sufficiently +severe to cause the patient to take to his bed. These so-called +"walking typhoid" cases are particularly dangerous, because they +serve to spread the disease organism more widely. + +A very considerable proportion of the people that recover from +typhoid fever still continue to harbor the typhoid bacillus in their +urinary and gall bladders. This condition may obtain for years, and +since such individuals are in perfect health and are ignorant of +their own condition, and since they give off the organisms more or +less constantly, they are often the cause of extensive milk borne +epidemics. Such persons are known as "typhoid carriers" and +constitute one of the gravest problems the public official has to +contend with in his struggle to prevent the spread of typhoid fever. + +Where outbreaks are caused by milk, they can readily be traced by +means of the milk route, as there are always a sufficient number of +susceptible persons, so that outbreaks of epidemic proportions +develop. In the Stamford, Conn., outbreak in 1895, 386 cases +developed on one milk route. In this case it was shown that the +carrying cans were thoroughly washed, but were later rinsed out with +_cold_ water from a polluted shallow well. + +The mode of infection of milk varies, but in general, the original +pollution is occasioned by the use of infected water in washing the +utensils, or a case of "walking typhoid" or bacillus carrier, who +directly infects the milk. In case of sickness in rural families, +some member of the household may serve in the dual capacity of nurse +and milkmaid, thus establishing the necessary connection. Busey and +Kober report twenty-one outbreaks, in which dairy employees also +acted in the capacity of nurses. The fact that the urine of a +convalescent may retain the typhoid germ in large numbers for some +weeks renders the danger from this source in reality greater than +from feces, as, naturally, much less care is exercised in the +disposition of the urine. + +The house fly is now regarded as one of the important means of +spreading typhoid fever, indeed it is often called the "typhoid +fly." The infectious material deposited in an open vault may serve +as a source from which the fly carries the organisms to milk and +other foods in the house or elsewhere. The protection of vaults and +the screening of every place where human food is handled or prepared +is the only protection. + +It should be emphasized that in the case of the tubercle organism, +no growth ever occurs in milk, but with the typhoid bacillus growth +is possible. It thus needs but the contamination of the milk with +the smallest particle of material containing them to seed the +milk. By the time it is consumed it may contain myriads of the +disease-producing organisms. + +=Diphtheria.= This is a highly infectious disease, affecting children +primarily and is characterized by the formation of membranous +exudates in the throat and air passages, which are teeming with the +causal organism, the diphtheria bacillus. This organism is capable +of forming highly toxic products, and it is to the effect of these +poisons that its fatal result is generally due. The organism is +thrown out from the body, in the main, through the mouth, the +surroundings of the patient being infected directly from the air, +and indirectly, by contact with polluted hands, lips, etc. Thus, the +germ deposited from the lips of a case of the disease, on the common +drinking cup, slate, lead pencils, toys, and the like, may easily +pass from child to child. Not infrequently, the causal organism +persists in the throat long after all evidence of membranous growth +has subsided, and so the child itself may act as a "bacillus +carrier." + +Not so many epidemics of diphtheria as of typhoid have been traced +to milk, but the evidence is sufficient to indict milk as a +disseminator of contagion. In several cases, the diphtheria germ has +actually been isolated from infected milk supplies. Actual growth of +the diphtheria germ is said to take place in raw milk more rapidly +than in sterilized. + +=Scarlet fever.= While the germ of scarlet fever has not yet been +isolated, and therefore its life history in relation to milk cannot +be depicted so accurately, yet milk-borne epidemics of this disease +are sufficiently abundant to leave no doubt but that this food +medium may sometimes serve as a means of disseminating such +troubles. Infection of the milk doubtless comes in the case of this +disease from direct contact with a person suffering from the malady. + +=Cholera.= While this disease is of no practical importance in +America, owing to its relative infrequency, yet outbreaks of cholera +have been traced to milk, in spite of the fact that the causal +organism is more sensitive to the action of acids than most +disease-producing bacteria. In several outbreaks in India, milk has +been the medium through which the disease was spread. Generally, +infection of the milk has been traced to the use of polluted water. + +=Children's diseases.= An exceedingly high mortality exists among +infants and young children in the more congested centers, especially +during the summer months. In the main, the cause of these troubles +is due to intestinal disturbances, and unquestionably, the character +of the food enters largely into the problem. As milk constitutes +such a large proportion of the diet of the young, and is so +susceptible to bacterial invasion, it would appear probable that +much of the trouble of this character is due to the condition of +this food supply. This is rendered more probable when it is +remembered that bottle-fed infants suffer a much higher mortality +than breast-fed children, due probably to the fact that the +lengthened period between the time the milk is drawn and consumed +permits of abundant bacterial growth. Much carelessness also +prevails among the poor in cities, relative to the care of utensils +used in feeding children. Nursing bottles often serve to infect the +milk. Where milk is pasteurized, or properly heated, it has been +found that the mortality rate has been greatly reduced, thus +indicating that the condition of the milk was directly responsible +for the death rate. In fact, the mortality from these indefinite +intestinal troubles probably exceeds that from all of the specific +infectious diseases combined. Improved care in handling this +sensitive food supply will do much to better conditions in this +direction. + +=Ptomaine poisoning.= Acute poisoning affecting adults as well as +children, not infrequently occurs from the use of foods of various +kinds. Cases of poisoning arising from the use of shell fish, canned +meats, ice cream, cheese, and other dairy products, are from time to +time reported. These troubles are due to the production of toxic +compounds, in the main, probably caused by bacterial decompositions. +Often such troubles may affect a number of persons, as at banquets +and such gatherings, thereby giving the semblance of an epidemic. +While such troubles are doubtless to be ascribed to bacterial +activity, they are not transmissible from person to person. + +In the case of troubles arising from ice cream and such confections, +the probable cause is due to the storage of milk or cream under +refrigerator conditions, where germ growth can go on in the product, +and yet the temperature be sufficiently low to prevent the usual +acid fermentations. + + + + +CHAPTER V. + +FERMENTATIONS OF MILK. + + +Milk, under normal conditions, is always contaminated with bacteria +coming from the most varied sources. If it is produced under clean +conditions, the number of bacteria will be small, but in any case, +the number of kinds of bacteria that find their way into milk will +be large. Many of them find in milk at ordinary temperatures +suitable conditions for growth; they use a portion of some of the +constituents of the milk as food, producing certain other compounds +that are known as "by-products." These by-products impart to milk a +taste and odor that is not found in fresh milk. The effect of the +action of bacteria may also be made evident by the change in the +appearance of the milk. When these various changes become evident to +the senses, either by taste, smell or sight, the milk usually is so +modified as to be unfit for many ordinary purposes. The preservation +of milk, a subject to be treated later, is a study of the ways of +preventing or retarding the growth of bacteria in milk, and thus +delaying the time when evidences of their action first become +apparent. + +Each class of bacteria produces more or less specific changes +in the milk as a result of their growth. Certain bacteria are +of the greatest benefit to the butter and cheese maker, while +others are distinctly harmful to the manufacturer of dairy +products. The changes produced by the different bacteria are called +"fermentations" of milk, each being most commonly named from the +most important by-product formed. + +=Acid fermentation of milk.= Fresh milk has a sweet taste and little +or no odor, but if it is allowed to stand at ordinary temperatures, +it sours; the taste is no longer sweet because the sweetness of the +sugar of the milk is masked by the acid produced from the +decomposition of a portion of the sugar by the bacteria. The change +in odor and taste of milk is apparent long before the appearance is +altered and increases in intensity as the acid-fermentation +progresses. The first alteration in appearance is most usually one +of consistency; the liquid milk is transformed into a semi-solid +mass. The terms "curdling" and "sour" are usually synonymous. Milk +is, however, often said to be sour as soon as the acid fermentation +has progressed to a point where it is evident to taste or smell. +This process of souring, or the acid fermentation is so common a +change that raw milk which does not show this type of fermentation +is looked upon with suspicion, and, usually, justly so. The process +in the past was thought to be something inherent in the milk, a +natural and inevitable change. It is now known that this is not so, +but that it is due to certain kinds of bacteria, and that if these +are prevented from getting into milk, it will not sour, but will +undergo some other less desirable type of decomposition. + +The acid-forming bacteria comprise but a very small part of the +total number of organisms that find their way into the milk during +its production on the farm, yet in sour milk scarcely any other +kinds of bacteria can be found. At ordinary air temperatures, the +acid-forming bacteria grow more rapidly in milk than do any other +forms, and the acid produced by them renders the milk an unfavorable +medium for the growth of other bacteria. This is the reason why milk +practically always undergoes the acid fermentation, although it is +contaminated with a host of other kinds of bacteria. If a mixture of +seeds is sown on low wet ground, certain kinds will grow best; if +the same mixture is sown on drier land, other types will find most +favorable conditions for growth, and the plants which appeared on +the low land will not appear. The same condition is found in milk +where the environment is most favorable for the acid-forming +bacteria. + +=Amount of acid formed in milk.= In this country the acidity of milk +is expressed as so many per cent of lactic acid. A milk that shows +an acidity of one per cent should, theoretically, contain one pound +of lactic acid in each one hundred pounds of milk. The acid +determined does not actually represent lactic acid, as there are +other substances in milk which act as acids, with the reagents used +in the present methods of determining the acidity of milk. For +instance, perfectly fresh milk has an apparent acidity of 0.13 to +0.18 per cent, although no fermentation has occurred. Other acids +than lactic are formed in the acid fermentation, but the entire acid +content is referred to as lactic when speaking of the acidity of +milk. When the developing acidity of milk reaches 0.25 to 0.3 per +cent, a sour taste becomes evident and the milk will curdle on +heating. When the acidity increases to 0.6 to 0.7 per cent, the milk +curdles at ordinary temperatures. The acidity continues, however, to +increase until it reaches about 1 per cent, which is the maximum +amount that will be produced in milk by the ordinary acid-forming +bacteria. Milk contains about 4 per cent of milk sugar, all of which +is fermentable. If this were all decomposed by bacteria, the acidity +of the milk would actually exceed 4 per cent. It is thus evident +that the reason why more acid is not formed in milk is not because +of any lack of sugar. The bacteria, like all other kinds of living +things, are injured by their own by-products, unless these are +constantly removed in some way; in milk the bacteria cannot escape +the action of the acid which they themselves have formed, +consequently growth ceases. The amount of acid formed is dependent +on the kind of bacteria present and on the composition of the milk. +Certain bacteria will not produce enough acid to cause the curdling +of the milk; still others will form 2 or even 3 per cent. These +types, however, do not play any important part in the spontaneous +souring of milk. + +In milk the acid first formed combines with the ash constituents and +the casein to form salts which do not seriously affect the growth of +the bacteria. Ultimately, the limit of the ash and casein to take up +acid is reached, and free lactic acid which is harmful to bacterial +growth appears. If the content of casein and ash constituents is +high, a higher degree of acidity will be reached than in a milk with +a lower content. If a large part of the volume of the milk is made +up of a compound that has no role whatever in the acid fermentation, +such as the butter fat in cream, the amount of acid formed per unit +volume of milk will be reduced, since in determining the acidity, a +definite volume of milk is taken, and the acidity is expressed, as +such a per cent of this amount. + +=Types of acid-forming bacteria.= When substances undergo +decomposition, it is a common belief that compounds offensive to the +odor and taste are formed; but such is not necessarily the case. The +products of the decomposition may be as agreeable and as harmless as +the compounds decomposed. Whether the decomposition products of any +substance are offensive or not is dependent on the kinds of +micro-organisms acting on it. There are forms of acid-producing +bacteria that change milk in odor, taste, and appearance, yet the +sour milk is not offensive in any sense of the word. Other bacteria +also sour the milk, but produce offensive odors and a disagreeable +taste. Thus, the acid-forming bacteria may be divided into two main +groups, which may be designated as desirable and undesirable. This +division is of importance to the butter and cheese maker and to the +consumer of milk. + +=Desirable acid-forming bacteria.= If milk is produced under clean +conditions, it is not likely to have a disagreeable odor or taste at +any time, even when it is sour; rather the taste is agreeable like +that of good butter milk. The curd is perfectly homogeneous, showing +no holes or rents, due to the development of gas, and there is but +little tendency for the whey to be expressed from the curd. This +type of fermentation is largely produced by the group of bacteria to +which has been given the name, _Bacillus lactis acidi_. + +The main by-product of this group of bacteria is lactic acid; small +amounts of acetic acid and alcohol, with traces of other compounds, +are also formed. The agreeable odor and to some extent the flavor of +milk fermented by these bacteria is due to other by-products than +lactic acid, for this has no odor and only a sour taste. The acid +fermentation of milk is often called the lactic acid fermentation. +In reality only the fermentation produced by the desirable group in +which lactic acid is the most evident by-product should be thus +called. + +[Illustration: Fig. 20.--Different Types of Curds. + +On the left a solid, homogeneous curd produced by desirable +bacteria; on the right, the curd produced by harmful bacteria. Note +the gas holes and free whey.] + +The bacteria of this group may enter the milk from the dust coming +from the coat of the cow. They are also found in the barn dust and +on cultivated plants. Under ordinary farm conditions, the larger +part of those found in milk come directly from the utensils. If the +milk is drawn under extremely clean conditions and care is taken to +sterilize the utensils, but few acid-forming bacteria of any kind +will enter the milk; under such conditions most of the acid-forming +bacteria will belong to the group in question. They find, however, +such favorable conditions for growth in milk that they develop more +rapidly than most other types with which milk becomes seeded; +consequently under normal conditions, they gain the ascendency and +so control the type of fermentation. + +The desirable type of acid-forming bacteria do not form spores; +hence, are easily killed by heating the milk. They can grow in the +presence or in the absence of free oxygen. In the bottom of a can of +milk or in the middle of a cheese, there is no air, yet these +bacteria grow as well under these conditions, as in milk exposed to +the air. The range of temperature for growth varies from 50° to 100° +F. but development is most rapid at 90° to 95° F. and about 1 per +cent of acid is formed. + +Another group of bacteria which may be classed among the desirable +acid-forming organisms is constantly found in milk. They have little +to do with the ordinary acid fermentation as they grow very slowly +at ordinary temperatures. If a sample of raw milk is placed at the +temperature of the animal body, the acidity will reach 1 per cent in +a few hours. Thereafter the acidity will increase slowly and may +reach three per cent or above. The continued increase in acid is due +to the growth of long rods of the _Bacillus Bulgaricus_ type, +which apparently enter the milk with the fecal matter. The nature of +the change produced by them in milk is very similar to that caused +by _Bact. lactis acidi_ in that lactic acid is the chief product; no +gas is produced and hence the curd is uniform in appearance. +Temperatures from 100° to 110° F. favor their development. Organisms +belonging to this group are used in the preparation of the fermented +milks now so widely sold in the cities. + +These desirable, acid-forming bacteria are of the greatest service +in every branch of the dairy industry, whether in butter or in +cheese making, or in the sale of milk in the city. The dairy +industry is dependent upon fermentative activity, as much as the +manufacture of beer or wine, and the main basis of this is the acid +fermentation of the milk by these desirable types of bacteria. + +Although milk contains a large amount of nitrogenous substances +(casein and albumen), it does not undergo putrid decomposition, as +do meat and eggs, not because it is not fitted for the growth of the +bacteria causing that type of change, but because the acid formed in +it stops the growth of the putrefactive bacteria. If a sample of +milk is placed in a stoppered bottle, it will have much the same +taste and odor at the end of several months as at the end of a few +days. The acid acts as a preservative, like the vinegar in pickles, +or the acid in silage and in sauerkraut. Meat placed in a stoppered +bottle which is then filled with milk will be preserved. + +The products formed in the decomposition of meat and eggs are not +only offensive but may also be injurious to the health of the +consumer. Milk that has been fermented by the desirable kinds of +acid-forming bacteria is not harmful. It is consumed in a variety of +forms (buttermilk, cottage cheese) as a common article of food and +its use is rapidly increasing. The preparation of the pure culture +buttermilks or artificially soured milks that are now so frequently +recommended for digestive troubles rests upon an acid fermentation +of this type. + +=Undesirable acid-forming bacteria.= Other types of bacteria capable +of forming substances that impart to milk an offensive odor and a +disagreeable taste not infrequently appear instead of the desirable +group. Instead of producing from the sugar of milk large quantities +of lactic acid, these types generate other acids, such as acetic and +formic, which impart a sharp taste to the milk. Besides the acids +the bacteria of this group form gases from the sugar of the milk. +Some produce small amounts of gas; others so much that the curd will +be spongy and will float on the surface of the whey. The +fermentation caused by them is often called a "gassy fermentation" +and is dreaded by butter and cheese makers since the gas is +indicative of bad flavors that will appear in the product. Gas may +also be produced in other types of fermentations to be discussed +later. + +This class of bacteria enters the milk with the dust, dirt, and +manure, in which materials they are especially abundant. No spores +are formed; hence they are easily killed by heating the milk. They +grow both in the presence and in the absence of free oxygen. High +temperatures favor their growth, most rapid development taking +place at 100° to 103° F. + +=Spontaneous fermentation of milk.= The normal souring of milk is due +to a mixture of these two groups of bacteria. The relative +proportions existing between the two in any sample of milk is +dependent on a number of factors, most important of which is the +degree of cleanliness exercised in the production of the milk. Where +careless conditions obtain under which dust and manure particles +find their way into milk, it becomes more abundantly seeded with +gas-generating bacteria, and consequently, the type of fermentation +is undesirable. If, however, the milk is drawn into clean utensils +and care is taken to exclude dirt, the pure lactic acid types are +able to control the character of the changes produced, and a clean, +pleasant tasting liquid results. It will be seen that things are +well arranged by nature; one of the most important food products +undergoes a type of decomposition that is not offensive and when +produced under clean conditions, the sour milk is as healthful a +food as is the fresh product. Thus there is every reason for +cleanliness in the production of milk, for cleanliness' sake and +because clean milk means better products, and greater returns to +everyone, producer and dealer. + +There are other kinds of acid-forming bacteria in milk but they are +of small importance compared with those just discussed. Some of the +bacteria derived from the inside of the udder of the cow form acid, +but these forms grow very slowly in milk at ordinary temperatures, +and have no influence on the keeping quality. + +[Illustration: Fig. 21.--Different Types of Curds. + +The flask on the left shows the soft curd produced by the bacteria +that curdle the milk without the production of acid. The flask on +the right shows the gassy curd formed by butyric acid bacteria in +heated milk.] + +=Sweet curdling fermentation of milk.= Samples of milk are sometimes +found that are curdled, but which do not taste sour, or have the +normal odor of sour milk. The curd is usually soft and the taste +bitter. It is evident that the curdling cannot be due to the same +factors as in the normal souring of milk. Such a change is similar +to the action of rennet which is used to curdle the milk in cheese +making. This ferment will curdle perfectly sweet milk, producing a +curd that looks like that formed in the acid fermentation of milk. +The cause of these sweet curdling milks, which appear from time to +time, is due to the introduction of certain bacteria which have the +power of secreting an enzyme resembling that found in rennet. In +such cases the milks curdle prematurely especially when warmed. The +curd may gradually disappear, for the bacteria also produce another +enzyme that digests the curd, and thus renders it soluble. When this +advanced phase becomes evident, it is often called the _digestive +fermentation_ of milk. This change is produced largely by +putrefactive bacteria of various kinds that find their way into milk +with dust and dirt. Many of them are spore formers; hence, are not +killed when milk is heated, as in pasteurization, while the +acid-formers are destroyed. Pasteurized milk is thus likely to +undergo the sweet-curdling fermentation, if it is kept for +any length of time. Raw milk rarely undergoes this type of +decomposition, since the rennet-forming bacteria under ordinary +conditions are unable to develop in competition with the +acid-forming bacteria. + +=Butyric acid fermentation of milk.= A fermentation that is much less +frequently noted than the two previously discussed is known as the +butyric fermentation, since butyric acid is the principal +by-product. The causal bacteria cannot compete with the ordinary +acid-forming bacteria in raw milk; hence it is most frequently noted +in pasteurized milk, since the organisms produce spores and are not +killed by the heating. Pasteurized milk under the action of the +butyric acid bacteria undergoes a gassy fermentation, developing a +pronounced acidity and the disagreeable odor of butyric acid, which +resembles that of rancid butter. The butyric acid bacteria are +anaerobic, and thus can grow in butter and cheese away from the air. + +=Slimy or ropy fermentation of milk.= A slimy or ropy condition of +milk is frequently noted on the farm and in the dairy. Several +causes for this abnormal condition exist. Sometimes the milk may be +slimy when milked from the cow. This occurs most frequently in the +case of inflammation of the udder which may or may not be due to +bacteria. The direct cause of the abnormal condition in milk is the +presence of fibrin and white corpuscles from the blood which form +masses of slimy material; in such cases the trouble does not +increase in intensity with age, nor can it be propogated by +transference to another sample of fresh milk. + +[Illustration: Fig. 22.--Slimy Milk. + +It does not mix with water when poured into it.] + +Another type of slimy milk is produced by the growth of certain +types of bacteria which enter the milk after it is drawn from the +udder. These may come from various sources. The bacteria concerned +belong to two groups: (1) those that grow best in the air and do not +form acid; (2) those that grow in the absence of air, throughout the +entire mass of milk and which form acid. The slimy condition is +noted in the milk only after the milk has been stored for some time; +it usually increases with the age of the milk and can be produced +in a second sample by transferring a little of the slimy milk to it. + +The fermentation produced by the aerobic bacteria is most often met +in bottled milk and cream during the warmer times of the year. On +account of their relation to oxygen, the growth is confined to the +surface of the milk and only the upper layer becomes slimy; thus +when the cream is removed, the abnormal condition is noted. The +sliminess is due to the mass of bacterial growth rather than to the +production of any specific substance in the milk. This trouble may +be of considerable economic importance to the dealer, as such +abnormal milk is objectionable for ordinary use, but as far as is +known, it is incapable of affecting the health of the consumer. + +In numerous outbreaks of this trouble the source of contamination +has been traced to infection from well water or a stream, as the +organisms causing the trouble are found naturally in water. Keeping +the milk in a tank in the pump house sometimes permits of troubles +of this sort, the water used for cooling giving opportunity for +contamination. Cattle wading in a stream sometimes pollute their +udders and so indirectly infect the milk. Such outbreaks rarely +persist for any considerable length of time as the common acid +organisms soon regain the ascendency. + +Creameries and cheese factories are sometimes troubled with +sliminess in starters. This seems to be due to some change which the +ordinary lactic acid bacteria undergo on long propagation rather +than to contamination of the starter. There are, however, types of +acid-producing bacteria that are able to form specific substances in +milk that are slimy in character. Two of these forms of slimy milk +are of economic importance. The slimy whey (lange Wei) of Holland +is added to milk in the manufacture of Edam cheese, apparently +serving the same purpose as the addition of the pure culture starter +in cheddar cheese making. In Norway, a sour, slimy milk +(taettemjolk) is used as food. It is produced by the addition of +some previously fermented milk. This beverage is also used in some +of the Norwegian settlements of Wisconsin, the original seed having +been brought from Norway, and the bacteria maintained by constant +propagation from one sample of milk to another. The milk has the +odor and taste of butter milk, but is not especially appetizing in +appearance to any one not accustomed to it; it is, however, as +harmless to health as is any other form of sour milk. It is not +known that any of these forms of slimy milk are distinctly harmful +to the quality of butter or cheese. + +=Alcoholic fermentation of milk.= The bacteria as a class are +incapable of producing alcohol in appreciable amounts. The alcoholic +beverages, beer, wine, and cider, are produced by the growth of +yeast, in such sugar containing liquids as fruit juices, extracts of +grains, etc. The common types of yeasts are incapable of acting on +milk sugar, but they can ferment glucose, maltose, and cane sugar, +forming equal amounts of alcohol and carbonic acid gas, which causes +the effervescence of fermented and carbonated drinks. There are, +however, some types of yeasts found in milk and its products that +are able to ferment milk sugar. + +All yeasts grow best in an acid medium, hence those fermenting milk +sugar find suitable conditions for growth in sour milk or whey. They +may at times become of economic importance in the cheese industry, +because of the contamination of the milk with large numbers of +them. The arrangement of the whey vat is often such that it cannot +be completely emptied and cleaned; the sour whey thus presents +favorable conditions for the growth of the lactose-fermenting +yeasts. The return of the whey to the farm in the milk can that is +often imperfectly cleaned may serve to contaminate the milk with the +yeast. In the making of Swiss cheese the whey is often so handled as +to favor especially the growth of such yeasts, and since this type +of cheese is prepared from sweet milk, the competition between the +yeast and the acid-forming bacteria is not so sharp as in the making +of cheddar cheese. The writers have found several instances where +considerable loss was occasioned in the Swiss cheese industry +through the development of gassy cheese due to this type of +fermentation. + +The yeasty or alcoholic fermentation may also be of importance in +butter making. In many sections of the country the milk is separated +on the farm and the cream is forwarded to the creamery at more or +less infrequent intervals. It becomes sour and if it has become +contaminated with yeasts, they will find favorable conditions for +growth in the acid medium. A large amount of carbon dioxide gas is +produced. Cans of gathered cream often foam to such an extent as to +run over, and in some cases actual explosions have occurred on +account of the great pressure caused by the gas. + +=Bitter fermentation of milk.= Bitterness in milk may be due to +bacteria that enter the milk after it is drawn from the cow, or it +may be caused by the feed consumed by the animal. It has been +previously shown that certain specific substances contained in the +food may be absorbed and reappear in the milk. If the animal eats +ragweed, lupines, or other plants containing bitter substances, the +milk is likely to have a bitter taste, which will be noticeable at +the time the milk is drawn. The milk of cows at certain advanced +stages of lactation may show a bitter taste, due to a change in the +ash constituents of the milk in which the lime salts are largely +replaced by salts of sodium. + +There are many bacteria that will impart to milk a bitter taste. +Milk that has undergone the sweet-curdling fermentation is likely to +be bitter, as is the ease with pasteurized milk. Some of the +acid-forming bacteria are able to develop a bitter principle, the +milk retaining a pleasant odor and having the normal amount of acid, +while the taste is intensely bitter. One of the authors (H) found in +the case of a Wisconsin brick cheese factory, that the usual acid +organism was almost wholly replaced by a bitter type. + +Storage of milk at very low temperatures is conducive to the +appearance of a bitter taste in milk, the explanation in this case +being that the acid-forming bacteria are unable to grow at a low +temperature, while some of the putrefactive forms can multiply and +develop these astringent or bitter by-products. + +=Miscellaneous fermentations of milk.= There are a number of other +abnormal fermentations in milk that occur so rarely as to be of but +little economic importance. Some, as the colored milks, are however, +quite striking, and on this account have had much attention directed +to them in the past. There are bacteria that are able to produce +various colored substances, such as red, yellow, and blue. In case +milk becomes seeded with large numbers of any of these kinds, it is +very likely to be colored by the growth. Red milk may be due to +bacteria, but more frequently is caused by the actual presence of +blood in the milk, due to a wound in the udder, or the effect of a +severe case of inflammation of this gland. Such a condition may be +readily distinguished by allowing the milk to stand for a short +time, in which case, if due to blood, the red corpuscles will soon +settle to the bottom of the container, while bacterial troubles +producing a red coloration are more evident on the surface. + +It is also claimed that certain bacteria may impart a soapy taste or +turnip flavor to milk. + +=Cycle of fermentations in milk.= If a sample of milk is allowed to +stand, it will undergo a certain sequence of fermentations that well +illustrates the principle that one type of organisms is dependent on +some other type to furnish suitable conditions for its development. +This cycle of changes that normally occurs in milk is as follows: +(1) The bacteria that come from the interior of the udder are the +first to develop, but usually the change they produce is not +evident. + +(2) Of the types that gain admission, subsequent to the milking, the +acid-producing species are able to adjust themselves most perfectly +to the conditions that obtain in milk. Within a few hours they +greatly predominate and soon the milk curdles under the production +of acid. Their growth, however, is soon stopped by the accumulation +of their own by-products. + +(3) The semi-solid curdled milk, on account of its acid reaction +then becomes a favorable medium for the growth of molds; a prevalent +form, known as _Oidium lactis_ usually develops as a white velvety +layer. The molds in their growth form alkaline by-products, which +tend to neutralize the acid reaction, so that in the course of two +to three weeks, if the layer of the milk is not too deep (an inch or +less), the chemical reaction of the milk becomes neutral or +alkaline. + +(4) The putrefactive bacteria which found their way into milk when +it was first drawn, and which have remained dormant in the sour +milk, now find favorable conditions for growth. As a result of their +activity, the milk soon undergoes a putrid decomposition, which is +marked by offensive odors. + +If the milk is placed under such conditions as will exclude the +growth of the mold, such as where the air is excluded from the +surface, the sour milk will remain in that condition for an +indefinite period, since the putrefactive bacteria are inhibited in +their development by the acid, in a manner comparable to the +preservation of pickles in vinegar, or the keeping of silage because +of the acid that is produced as a result of the changes that the +plant tissue undergoes when excluded from the air. The preservative +effect of acids is of much importance in the case of certain dairy +products (see Chapter VIII). + +=Fermented drinks from milk.= Within the last few years a great deal +of attention has been directed toward the preparation of various +kinds of drinks from milk. The use of such beverages has rapidly +increased. Butter milk is one which meets with the greatest +approval. The true butter milk from cream that has been soured by +the desirable acid-forming bacteria has a mild agreeable acid taste, +wholly free from any sharpness that is often noted in butter milk +made from cream in which considerable numbers of the undesirable +acid-forming bacteria have grown. Butter milk made from pasteurized +cream soured with pure cultures will have good keeping qualities and +is a most healthful drink for all classes of people, even for young +children. + +Butter milk is also prepared by allowing milk to sour and then +breaking up the curd by stirring. If the type of fermentation is +controlled as may be done (see Chapter VII), such a form of +fermented milk is a most desirable drink. It is probably as +healthful and has all the therapeutic properties that are ascribed +to other forms of fermented milks such as the Bulgarian "Yoghurt." + +This type of fermented milk is produced by an acid-forming organism +that can form large amounts of acid, 2.0 or 3.0 per cent. The casein +is dissolved to some extent and the remainder so changed, that it +will remain in suspension for a long time in a finely divided form, +after the curd has been broken up. Such milk is sold under various +names at home and abroad. One of the authors (H) has found such +organisms in practically all milks examined. If raw milk is kept +warm (98° to 100° F.) in a stoppered bottle which is filled full, +the acidity will be found to increase slowly from day to day, +reaching a maximum in ten to fourteen days. If the milk is then +examined, it will be found to contain large numbers of an +acid-forming organism very different in appearance from the bacteria +causing the rapid souring of milk at ordinary temperatures. This +organism is very similar if not identical with the one found in the +Bulgarian milk to which the name _B. Bulgaricus_ has been given. The +use of the milk fermented by this organism has spread rapidly +because it is claimed by certain European bacteriologists that it +has a favorable effect on the health of people, especially those +suffering from intestinal troubles. It is not at all certain +that ordinary sour milk or butter milk will not have the same +effect; in fact in many of the fermented milks sold in Europe, _B. +Bulgaricus_ has not been found, but only the ordinary lactic acid +bacteria. + +Several alcoholic drinks made from milk, such as kefir and koumiss, +have been originated among the nomadic tribes of Western Asia. Kefir +is prepared from cow's milk by adding the kefir ferment in the form +of grains which contain a number of kinds of bacteria and a yeast. +The acid-forming bacteria impart a sour taste to the fermented milk, +while the yeast forms carbon dioxide and about two per cent of +alcohol. If the milk is allowed to ferment in stoppered bottles, the +resulting product will be an acid effervescing drink, which is +claimed to be more easily digested than sweet milk. This drink is +used frequently in the treatment of invalids but it is improbable +that it is more easily digested than ordinary soured milk or butter +milk. The grains are removed from the fermented milk, and are then +added to a quantity of fresh milk, or they may be dried and kept for +future use. When needed again, they are soaked in water, then added +to the milk. + +Koumiss is made in Russia from mare's milk and has much the same +composition as kefir. In America and Europe it is made from cow's +milk, by adding cane sugar and compressed yeast. The yeast ferments +the cane sugar while the acid-forming bacteria ferment the milk +sugar. There is thus obtained a drink that is similar in composition +to the real koumiss, in which both the acid and the alcohol come +from the fermentation of the milk sugar. In koumiss and kefir the +curd is very finely divided and will remain in suspension for a long +time as with butter milk. + +=Determination of the cause of taints in milk.= It is often of the +greatest importance to be able to locate the cause of abnormal +odors or tastes in milk, since methods for overcoming the trouble +can be intelligently applied only when the actual cause is known. An +abnormal condition may be caused either by the direct absorption of +odors before or after the milk is drawn from the animal, or it may +be due to bacteria. If the milk appears bad-flavored when first +drawn, and if such taint becomes less pronounced as the milk becomes +older, it is likely that the trouble is due to some characteristic +of the feed. Certain feeds, like green rye, rape, cabbage, and +certain of the root crops, like turnips, impart a strong odor to +milk, if the same are fed shortly before milking. If the tainted +condition appears only some time after the milk is drawn, it may be +due to the direct absorption of taints from the surroundings in +which the milk is kept, or it may be caused by bacteria. These +causes can often be differentiated, by noting whether the taint +tends to increase in intensity with age. If such is the case, it is +likely that the cause is of germ origin, but if the reverse is true, +it cannot be ascribed with certainty to bacteria and recourse must +be had to other methods, such as the transfer of a small quantity of +the tainted milk to a sample of perfectly fresh milk, or preferably +to some milk that has been heated to the boiling point and then +cooled. In the case of an odor due to direct physical absorption, it +will not appear in the inoculated sample, since the small amount +transferred is not sufficient to be noted. If it is due to living +organisms, the inoculation of the smallest quantity into a fresh +sample is likely to reproduce the same change as originally noted. + +=Tests for the bacteriological condition of milk.= Within certain +limits milk can be indirectly examined as to its bacterial content +without any special equipment. Milk when drawn from the cow has an +apparent acidity ranging from 0.16 to 0.18 per cent. By the use of +any of the methods of determining acidity in milk, much can be told +concerning the number of bacteria in the milk, and hence concerning +its keeping quality. Milk that has an acidity of over 0.2 per cent +is certain to contain many bacteria, and consequently will keep +poorly. Such milk is of low value for market milk, but may not be +objectionable for butter or cheese making. If the acidity is below +0.2 per cent, but little can be told as to the numbers of bacteria, +since any increase in acid is always preceded by an enormous +increase in the numbers of acid-forming bacteria. + +A more important test than the acid test, from the standpoint of the +butter and cheese maker, and even the milk dealer, is the +fermentation test. In its simplest form, it consists in placing a +sample of the milk to be tested in a warm place and noting the time +required to curdle and the type of curd formed. In this country the +fermentation test has been largely supplanted by the Wisconsin curd +test which possesses the advantage of detecting the presence of +bacteria harmful in cheese making, especially the gas forming +bacteria. + +The curd test is helpful in detecting the source of an abnormal +condition in a milk supply coming from diverse sources. The milk +furnished by each patron can be tested separately and the trouble +located, perhaps in an individual herd; the offending herd +determined, the test may then be used on the milk of individual +cows. The cheese maker and the milk dealer should be able not only +to detect which of the patrons furnish him poor milk, but he should +be able to give the patron definite instructions how to avoid the +sources of such trouble. This information can be given only when +the source is positively known. + +[Illustration: Fig. 23.--Curd Test. + +A good curd obtained from milk containing no harmful bacteria but +many desirable acid-forming organisms.] + +The Wisconsin curd test is made as follows: Samples of the milk to +be tested are placed in sterile pint fruit jars. The milk is warmed +to 90° F., ten drops of rennet are added to each sample, and as soon +as the curd is solid, it is cut into small pieces with a case knife +so as to facilitate the expulsion of the whey. As the curd settles +to the bottom of the vessel, the whey is poured off at intervals so +that a pat of firm curd is left. As the milk curdles the bacteria +are enmeshed and are carried with the curd. The jars are kept at a +temperature of 100° to 105° F., since this temperature is favorable +to growth of the bacteria that are sought, the gas-forming +organisms. At the end of ten to twelve hours, the jars are examined; +if the curd is solid, the texture firm, not mushy or slimy on the +surface, if the odor is agreeable, it indicates that the milk +contains few or none of the undesirable forms of bacteria. If the +curd is full of gas holes, it is apparent that undesirable bacteria +are present and under such circumstances the curd will not have an +agreeable odor. If the gas-forming bacteria are numerous, the curd +may even be spongy from the abundance of gas holes, and the +undesirable odor more pronounced. Such curds are tough and rubbery. +In some cases a bad flavor or odor is apparent even though the +texture of the curd is not open and full of holes. The curd, the +surface of which is slimy indicates undesirable organisms. A solid +curd of agreeable odor is indicative of the presence of the +desirable acid-forming bacteria. Such a milk is excellent from the +standpoint of the butter or cheese maker, but may not be so +desirable from the standpoint of the milk dealer on account of its +poor keeping qualities. On the other hand a milk suitable from the +standpoint of the milk dealer, on account of its low germ content, +and hence good keeping quality, may give a poor curd test. It is +certain to contain some bacteria, especially those from the interior +of the udder while it may contain none of the desirable acid-forming +organisms without which a curd of good texture and flavor can not be +obtained. The bacteria in the clean milk will grow rapidly at the +high temperatures at which the curds are kept and the changes they +will produce as to flavor and odor may be undesirable. The milk +might be judged as poor when in reality it might be a most excellent +sample, and if kept at the ordinary storage temperatures, it might +keep for days. The test when used for market milk should be +interpreted with this in mind. + +[Illustration: Fig. 24.--Curd Test. + +The curd obtained from milk containing many gas-forming bacteria. +The irregular, angular holes are mechanical, due to the imperfect +fusion of the pieces of curd.] + +If the results are to be of any value, the test must be made with +care to avoid all sources of error; the tester must know that the +bacteria causing the gas and bad flavors in the sample were +originally present in the milk at the time the sample was taken, and +that they have not come from the containers used or from other +sources. To insure these conditions the jars must be thoroughly +cleaned and then sterilized just before use by placing them in cold +water and bringing them to the boiling point, or sterilized by a +thorough steaming. The sample of milk of a patron must be taken so +as to avoid contamination from the milk of the other patrons. This +can best be done by filling the jars as the milk is poured from the +patron's can into the weigh can. In cutting the curds, the knife +used must be dipped in hot water between each test to cleanse the +same. In short, the test should be carried out with great care so +that the tester is certain of the results obtained. + +Other tests for the bacteriological condition of milk will be +described in Chapter IX. + +=Overcoming abnormal fermentations.= The lactic acid bacteria are +often looked upon as normal to milk, and it is certain that they are +to be classed as harmful, only as they injure the keeping qualities +of milk. In milk designed for butter and cheese their presence is +necessary. At times these desirable forms of bacteria may disappear, +and be replaced by less desirable types. In one case it was observed +that the usual lactic bacteria had been replaced in a cheese factory +supply by an acid-forming organism that produced an intensely bitter +taste in the milk, thus rendering the cheese of no value. When such +harmful forms appear, they must be overcome, and the normal types of +bacteria replaced. A thorough cleaning of the milk utensils, +attention to the cattle and all places from which such bacteria may +find their way into the milk is often sufficient to cause a +disappearance of the trouble. If the acid-forming bacteria have +disappeared, the inoculation of the milk with cultures in ways later +to be discussed is often of advantage. At times more stringent +measures must be employed in order to destroy the harmful bacteria, +such as the use of strong disinfectants. + +=Disinfection and disinfectants.= If any building or room becomes +infected with disease-producing bacteria, or if organisms causing +abnormal fermentations become established in a factory, the use of a +disinfectant that will destroy with great rapidity the life of +bacteria is necessary. The disinfection of all types of dairy +apparatus and utensils can be accomplished by thorough cleansing, +and by the use of steam or boiling water. The disinfection of rooms +and stables cannot be so readily accomplished. + +Consideration must always be given to the resistance of the organism +it is desired to destroy. Those that form spores are very resistant +toward all chemical agents, while those that do not produce these +resistant bodies are easily killed. In the dairy and factory, it is +often necessary to destroy the organisms that develop in decomposing +organic matter. Here, as in all disinfection, a thorough cleaning +should precede the application of any disinfectant. Some chemicals +act as deodorants, _i.e._, destroy the offensive odor, without +removing the cause. It is impossible effectually to destroy bacteria +embedded in a mass of organic matter, and through the removal of the +material itself, the larger part of the bacteria will be removed. +The disinfectant then comes in direct contact with the surface to be +disinfected, consequently destroys the bacteria not removed in the +cleaning. + +All places in which dairy work of any kind is done should be +provided with an abundance of light and air. The direct rays of +the sun have a powerful disinfecting action, and light makes evident +accumulations of dirt that in a darker room would be unnoticed. +Ventilation keeps the rooms dry and thus prevents the growth of mold +and the development of a musty odor. + +Disinfectants are divided into two classes: (1) solid materials used +in suspension, or in watery solutions; (2) gaseous substances. The +latter are preferable for room disinfection when their use is +permissible, for the gas penetrates to every part of the space, even +into the cracks. Gaseous disinfectants can only be used when the +space is tightly closed, for the gas must be confined for several +hours in the room, in order to make the process effective. Such +disinfectants can often be used to advantage in the treatment of +refrigerators and cheese rooms to destroy mold spores. In less +tightly closed spaces, reliance must be placed on the use of the +solid or liquid disinfectants. + +=Lime.= Quick lime or stone lime has a considerable disinfecting +action. On exposure to the air, quick lime becomes air slaked, and +then has no disinfecting action whatever. Water-slaked lime used in +the form of white wash, lime water, or the powder is effective. +Air-slaked and water-slaked lime are similar in appearance, but a +difference can be noted by placing a particle of each on the tongue; +the air-slaked tastes like chalk while the water-slaked material +causes the tongue to burn. + +White wash is one of the most effective agents that can be used in +the disinfection of barns, milkrooms, etc. Besides being a fairly +strong disinfectant, it has a tendency to absorb odor, it encrusts +the walls and lightens the interior of rooms. It can be applied with +a brush or with a spray pump. + +=Carbolic acid and cresol compounds.= These substances are among the +cheapest and best disinfectants, but their use in the dairy is not +advisable, on account of the penetrating and lasting odor. They can +be used to advantage on the farm. Some of the proprietary compounds, +as Zenoleum, Kresol, etc., are easily applied, since they mix +readily with water in all proportions, forming a milky-white +emulsion that can be easily applied. They are less caustic and less +poisonous than carbolic acid. + +=Corrosive sublimate.= Corrosive sublimate is the most efficient +disinfectant under ordinary conditions. It is such an intense poison +that it must be used with caution in places to which stock have +access, or in the dairy. A solution of one part of the salt to a +thousand parts of water (half ounce to 4 gallons of water) is the +standard generally used. + +For gutters, drains, and waste pipes in factories, ferrous sulphate +(green vitriol), and copper sulphate (blue vitriol), can be used to +advantage. They are to be classed as deodorants rather than as true +disinfectants. Since they have no odor of their own, they can be +used in any amount in the dairy. + +=Sulphur= can be used to advantage in the destruction of mold spores +in cheese rooms, but the effect of the vapors of burning sulphur on +germ life is relatively slight, unless there is an abundant supply +of moisture in the air of the enclosed space, in which case +sulphurous acid is formed which has a much greater effect. To have +the desired effect sulphur should be burned at the rate of three +pounds to each one thousand cubic feet of space, and the room kept +sealed for at least twelve hours. If the sulphur is placed in an +iron kettle which is set in a vessel of water, danger from fire +will be avoided, and the heat generated by the burning sulphur will +evaporate sufficient water to increase the effect of the fumes. + +=Formalin.= Another disinfectant that may be used as a liquid or as a +gas is formalin, which is a watery solution of the gas, +formaldehyde. It is much more powerful in its action than sulphur, +and has a great advantage over corrosive sublimate and other strong +disinfectants in that it is not so poisonous to animals as it is to +bacteria and fungi. + +It can be used as a solution (one to five per cent) for the washing +of woodwork, or for the treatment of any object, since it has no +corrosive action. It can also be employed as a gaseous disinfectant +for the treatment of rooms. It is most conveniently applied by +suspending large cloths in the room and spraying them with the +solution, then closing the room for a number of hours. + +=Bleaching powder.= Chloride of lime, or bleaching powder as it is +often called, is a good disinfectant, as well as a deodorant. It is +used as a wash in the proportion of four to six ounces to a gallon +of water. It must be used with care in factories since the free +chlorine that is given off has a penetrating odor. + + + + +CHAPTER VI. + +PRESERVATION OF MILK. + + +It has been shown in a previous chapter that milk becomes +contaminated with a multitude of bacteria not only on the farm where +it is produced, but during the various stages prior to its use. Many +of the bacteria which find their way into milk are readily able to +develop, and by their growth, render the milk unfit, or even harmful +for human food. With the most stringent precautions that can +reasonably be taken, it is impossible to avoid all contamination; +hence, all grades of milk will soon spoil, unless some means of +preservation is employed. Indeed, of all the foods classed as +perishable, milk is the one that most rapidly deteriorates. Produced +under ordinary conditions, it is unfit for ordinary use in a few +hours if kept at 70° F. + +There are three possible ways by which milk may be preserved: (1) +The removal of bacteria that have gained entrance to it; (2) The +prevention of growth of the contained bacteria; (3) The destruction +of the contained organisms. In practice at least two and sometimes +all of these methods are employed. The prevention of contamination, +a subject discussed in Chapter III is in reality one of the most +efficient means of preserving milk. In milk production, as +elsewhere, prevention is preferable to cure. Milk produced under +such conditions that its germ content is but a few thousand per +cubic centimeter will keep much longer than that handled in the +ordinary manner. + +It might naturally be supposed that any method by which dirt is +removed from milk would improve the keeping quality of milk, due to +the reduction of bacteria, yet while the straining of the milk at +the time of milking removes dirt of various kinds, it does not +appreciably enhance the keeping quality, owing to the fact that the +bacteria adherent to the dirt particles are washed off in straining, +and pass through the pores of the strainer. + +=Filtration of milk.= It is possible to remove all bacteria from water +and other fluids and thus render them sterile by passing through +filters of unglazed porcelain. This process can not be used with +milk for the fat globules are larger than the bacteria (see Fig. 6) +and any process that would remove the latter would also remove the +former. The term "filtration" is applied to a process used in some +European cities for the removal of the insoluble dirt that has been +introduced into the milk. Suitable containers are filled with layers +of coarse sand at the bottom and with finer sand at the top. The +milk is introduced at the bottom and is forced upward through the +sand. Such a filtering process is a very efficient means of removing +the dirt; but unless the filters are kept scrupulously clean, the +bacteria are likely to grow in the filtering material, so that the +number of organisms in the milk may actually be increased by the +filtering process. It is necessary to remove the sand daily and +thoroughly wash and sterilize the same. The extra care required in +keeping these sand filters in sanitary condition has been the great +objection to their employment in this country. Filters of other +material such as cellulose have been employed but with no marked +success. + +=Clarifying milk.= A much more efficient and less troublesome means of +removing the insoluble foreign particles from milk is to pass it +through a cream separator, allowing the cream and skim milk to mix +in the same container. The slime that collects on the wall of the +separator bowl is made up of dirt, casein, bacteria, and the +cellular debris from the interior of the udder. The bacteria are +heavier than the milk serum, and would, therefore, be deposited on +the wall of the bowl were it not for other factors that in a measure +prevent this. The movement of the fat toward the center of the bowl +carries into the cream a considerable proportion of the bacteria in +the milk. The slime will always contain many more bacteria than the +milk, but the per cent of bacteria thus removed is relatively low, +due to the small amount of slime obtained from the milk, so that the +actual effect of clarification on the keeping quality of milk is +insignificant. The complete removal of all insoluble and therefore +visible dirt is, however, regarded of sufficient value to warrant +the use. + +Machines designed especially for the clarification of milk are now +widely used. They differ from the cream separator in that the milk +is introduced at the outside of the bowl and hence there is no +separation of the fat from the serum. It is claimed that the removal +of the dirt, cells from the interior of the udder and bacteria is as +efficiently done as when the separator is used. The advantages +claimed for the machine are that it has no effect on the subsequent +gravity creaming of the milk and that less power is demanded than +for the separator. + +From the standpoint of the consumer, all processes by which dirt is +removed from milk are objectionable, since they make the milk +appear cleaner and better than it really is, the harm having been +done when the dirt with the adherent bacteria found its way into the +milk. The removal of the foreign matter that has been introduced +into the milk will have but little effect in reducing the number of +bacteria, since a large part of the organisms will have been washed +off the insoluble material. All of these processes improve the +appearance of the milk but have little or no influence in increasing +its keeping quality or its healthfulness. + +=Preservation by cold.= The only legitimate way of preventing the +growth of bacteria in milk is by holding it at temperatures at which +the ordinary forms of bacteria cannot thrive. Bacterial growth is +greatly checked at temperatures approximating 50° F., or below, +although certain types multiply at the freezing point or slightly +above. If food products are actually congealed, no germ growth +occurs, and they may be kept quite indefinitely, but this process +cannot be successfully applied to milk, as the fat and casein are +physically changed, so that a normal emulsion can not again be made +when the frozen milk is melted. The fat separates in visible masses +as though the milk had been partially churned. On account of this +fact milk must be stored at temperatures above the freezing point. +In Denmark efforts have been made to preserve milk, that is to be +shipped long distances, by freezing a portion of the milk, and +placing a block of the frozen milk in each can after cooling the +main mass of milk nearly to the freezing point. Even this method has +not proven practical, and at present reliance is placed on thorough +chilling of the milk. At 32° F., the lactic bacteria cannot grow, +but other types, such as certain of the putrefactive forms grow +slowly; the milk may, therefore, have no objectionable odor or taste +and yet be swarming with bacteria. In cities the practice is +followed of placing cream in cold-storage during the cooler periods +of summer in preparation for an increased demand, during hot weather +or on holidays. It seems probable that poisoning from ice cream may, +at times, be due to the use of such cream. + +=Preservation by the use of antiseptics.= Many chemical substances +prevent the growth of bacteria when added to food supplies; such +substances thus used are called _preservatives_. In the past some of +these have been used in milk to a great extent, but at present, on +account of stringent pure food laws, they are employed only to a +slight extent. There is a great temptation for the small milk dealer +in the city to employ them to preserve the excess of milk from day +to day, as through the use of a few cents worth of some preparation, +many dollars worth of milk may be kept from spoiling until it can be +sold to the unsuspecting consumer. + +Formalin has been most widely used in milk because it is a most +efficient preservative; it is cheap and cannot be detected by the +consumer, although it injures the digestibility of the casein. One +ounce will keep one thousand pounds of milk sweet for twenty-four to +forty-eight hours. Borax, boric acid, and salicylic acid have also +been used, but these substances must be employed in much larger +quantities than formalin. Bicarbonate of soda has sometimes been +used although it is not a true preservative. Its effect is based +upon the neutralization of the acid produced by bacterial growth. +The treated milk does not taste sour so quickly, and the curdling of +the milk is also delayed. + +Many proprietary compounds for milk preservation have been placed on +the market in the past, but the use of all of these is illegal in +most states. The federal law also prohibits their use in all dairy +products that pass into interstate commerce. + +Within recent years a method for the preservation of milk was +introduced by a Danish engineer, Budde, which consists of adding to +milk a very small amount of peroxid of hydrogen which is a very +efficient antiseptic. The peroxid is decomposed by some substance in +the milk; the products of decomposition being water and free oxygen. +The peroxid together with the application of heat at a comparatively +low temperature (122° F.) is sufficient to destroy the larger part +of the bacteria in the milk. Practical difficulties are encountered +in the commercial application, so that it is probable the process +will never be a commercial success. + +For the preservation of composite samples of milk for analytical +purposes, such as the Babcock test, strong disinfectants, as +corrosive sublimate, are employed. This material is very poisonous, +and leaves the milk unchanged in appearance. Some coloring matter is +therefore usually mixed with the sublimate in making the +preservative tablets, so as to render their use more conspicuous. +Corrosive sublimate not only stops all bacterial growth, but quickly +destroys the life of the cells. Bichromate of potash is generally +employed in the preservation of composite samples for the Hart +casein test. + +=Destruction of bacteria in milk.= Actual destruction of the life of +bacterial cells by heat is one of the most important ways for +preserving milk. Heat easily destroys the vegetating, growing +bacteria, while the spores, of which there are always a number in +milk, are very resistant. If, however, the growing organisms are +destroyed, the milk will keep much longer than if it had not been so +treated. + +The process of pasteurization was first used by the French +bacteriologist, Pasteur, for the treatment of the wines of his +native district which were likely to undergo undesirable types of +fermentations due to bacteria. From the wine industry it was applied +in the brewing industry, and was later found to be of the greatest +service in the dairy industry. The process of pasteurization may be +briefly defined, as the heating of milk to temperatures, varying +from 140° F. and upward for a longer or shorter time, and +subsequently cooling to a low temperature, so as to prevent the +germination of the spores that are not destroyed by the heating. + +=Effect of heat on milk.= When milk is heated it undergoes more or +less profound changes, depending on the temperature and time of +heating. Some of these changes are of practical importance, since +they are more or less evident, and objectionable to the consumer. + +In raw milk the fat globules are largely found in larger or smaller +aggregates, rather than uniformly distributed throughout the serum. +The surface of a mass of fat globules is smaller in proportion to +the volume of the mass than is the case with single globules, hence +globule clusters encounter less resistance in their passage through +the serum, either as they rise to the surface in gravity creaming, +or in the separator bowl. If these clusters are broken up, so +that the globules are uniformly distributed, the milk will cream +much less rapidly and completely. In the process known as +"homogenization" of milk, the individual fat globules are broken +into such small globules, that they cannot overcome the viscosity +of the serum, and they remain distributed throughout the milk. In +such cases, no cream rises, and even the cream separator is unable +to remove the fat from such milk. + +In selling bottled milk, it is highly desirable that the cream line +should show distinctly. In normal milk, this line forms in a few +hours, but where milk is heated to a high temperature, and agitated +at the same time, the clusters of fat globules are broken apart and +the creaming power injured. This physical change is dependent not +only on the temperature, but also on the time of exposure. A +momentary exposure at 160° F., or for 20 minutes at 145° F., is +about the maximum limit which can be applied to milk without +material injury to the creaming property. + +[Illustration: Fig. 25.--Fat Globules in Raw Milk. + +In raw milk the fat globules are in masses of varying sizes. These +rise to the surface quickly in gravity creaming.] + +The body or consistency of pasteurized cream may be restored by +allowing the cream to stand for several days at low temperatures, +or by the addition of a small amount of sucrate of lime. This +substance, known to the dairy trade as "viscogen," is made by adding +to a thick solution of cane sugar, some freshly slaked lime. The +sugar solution permits of the dissolving of a much larger amount of +the lime than is possible in water. When the liquid is allowed to +settle, the clear solution is then decanted off and is used at the +rate of about one part to 100 to 150 parts of cream. The fat +globules are, by its action, brought into aggregates and the body of +the cream thus restored. Viscogen contains nothing that is at all +harmful, but milk and cream to which it is added must be sold under +some distinctive name as "visco-cream," since the laws of +practically all states do not allow the addition of any substance +whatever to milk or cream. + +[Illustration: Fig. 26.--Fat Globules in Heated Milk. + +When milk is heated the masses of globules are broken up and fat +globules are uniformly distributed throughout the milk.] + +[Illustration: Fig. 27.--Creaming of Milk. + +The cylinder on the left contains raw milk; that in the center, milk +heated to 140° F. for twenty minutes; on the right, milk heated to +160° F. for twenty minutes. The dark line indicates the depth of the +cream after twenty-four hours. The breaking up of the fat globule +clusters delays greatly the rising of the cream.] + +Heated milk has a taste unlike that of raw milk; to one not +accustomed to it the taste is objectionable. This change is due to +some extent to the expulsion of the carbon dioxide from the milk. +The insipid taste of boiled water is, in part, due to its freedom +from carbon dioxide. The production of this cooked flavor is +dependent upon the time and temperature of exposure. It has been +claimed that heated milk is less digestible than raw, and a +considerable amount of experimental work has been done, both on +animals and children, in order to determine the relative +digestibility of heated and raw milk. The results obtained have been +contradictory. It is claimed that heated milk causes such diseases +as rickets, scurvy and marasmus in children. It is probably true +that milk heated to the boiling point is less fitted as food for the +young child than raw milk, but, on the other hand, it has not been +proven that properly pasteurized milk is an unsuitable food for +children. The best evidence has been accumulated in recent years, in +many of the large cities of this country and of Europe, where +pasteurized milk has been used with the greatest success in the +feeding of children of all ages. + +The heated milk does not curdle readily when rennet is added due to +the precipitation of the lime salts by heat. The curdling power can +be restored by the addition of soluble lime salts or of acids. + +=Purpose of pasteurization.= There are two reasons for the +pasteurization of milk: (1) To improve the keeping quality; (2) To +destroy any pathogenic bacteria it may contain. The first may be +called the economic reason; the second, the hygienic reason fur +pasteurization. In the selection of a proper pasteurizing +temperature, two factors must be taken into account: First, the +effect of heat on milk, and second, the temperature necessary to +destroy those forms of bacteria that are of the greatest importance, +as far as the keeping properties are concerned, and the pathogenic +bacteria that might possibly be present in the milk. The lactic +acid bacteria are non-spore-bearing and are not resistant to heat. +Most of them are destroyed when the milk is heated to 140° F. for +fifteen minutes or to 160° F. for a moment. To insure proper keeping +quality, somewhat higher temperatures must be employed, such as 145° +to 150° F. for fifteen to twenty minutes. + +Milk pasteurized at these temperatures will, as a rule, undergo an +acid fermentation in much the same manner as will raw milk. The rate +with which the acid develops is of course much slower than in the +raw milk, due to the destruction of 95 to 99 per cent of the +acid-forming bacteria. If the milk has been pasteurized at higher +temperatures, the acid fermentation may not appear. The spores of +the spore-bearing organisms will be left; these may germinate and +cause their characteristic change in milk, which, as previously +noted, is usually a sweet-curdling or a digesting fermentation. +Since the changes they produce in the milk are not evident at first, +it might be used as food even though it was so far advanced in +decomposition as to be undesirable or even harmful as food. Indeed +one of the objections urged against pasteurization is that it +destroys the natural safe guard, the acid-forming bacteria. Many +people are so accustomed to use this as the indication of spoiled +milk that they will use milk long after it should be used if it does +not show an acid fermentation. + +The butyric acid organisms are spore forming and may at times +produce their characteristic fermentation in pasteurized milk. The +milk shows gas formation and develops an objectionable odor. + +The pathogenic bacteria most likely to be present in the milk are +the typhoid and the tubercle organisms. The typhoid bacillus is no +more resistant to heat than the ordinary acid-forming bacteria, and +all milk that has been heated, so as to impart to it satisfactory +keeping properties, will certainly be free from typhoid bacilli. It +has sometimes been asserted that the tubercle bacillus is very +resistant to heat; some claiming that it is necessary to heat milk +to 200° F. in order to destroy it. Other experimenters have asserted +that lower temperatures would suffice, but the temperatures were +still above those at which the milk is physically and chemically +changed by the heating process. More recent work has shown that not +all sources of error were avoided in the earlier attempts to +determine the thermal death point of the tubercle bacillus, as, for +example, it has been shown by the authors that the "scalded film" +that forms on the surface of milk when heated in an open vessel will +protect the bacteria imbedded in it. It has also been shown by the +authors that a temperature of 140° F., for twenty minutes or 160° F. +for one minute will destroy the tubercle bacilli in milk, in case +the heating is done with sufficient thoroughness to insure all +particles of the milk being heated to the same temperature for these +periods of time. + +The pasteurization of milk can be done in such a manner as to impart +to it good keeping qualities and to insure its freedom from +pathogenic bacteria, and yet not impair its physical and chemical +properties, but much of the so-called pasteurized milk placed on the +market is not treated in accordance with proper hygienic methods. + +[Illustration: Fig. 28.--The Pott's Discontinuous Pasteurizer. + +The milk is placed in the inner compartment. For heating and +cooling, hot or cold water is passed between the jackets.] + +=Methods of pasteurization.= In order to destroy the bacteria in milk, +it is necessary that the milk be heated for a varying time dependent +upon the temperature employed. A lower temperature for a +considerable period may exert the same effect on the bacteria as a +higher temperature for a shorter time. In practice, two types of +pasteurizing machines are employed, depending on the temperature at +which the milk is to be treated. The discontinuous machines or +intermittently operated pasteurizers are those in which the milk is +heated for any desired time at any temperature. Such machines +consist of jacketed containers the inner receptacle being filled +with milk, while the outer space between the walls is filled with +circulating hot water or steam. The milk is kept agitated by the +rotation of the machine. After it is heated, it is cooled in the +same container by replacing the hot water first with cold water, +then ice water. The disadvantage of this process is that the +capacity of the machine is limited which precludes its use in places +where large quantities of milk or cream are handled; for the +pasteurization of limited quantities, it is very successful, as +every particle of milk or cream is under the direct control of +the operator and may be thoroughly and efficiently treated. + +As pasteurization was introduced for the treatment of market milk, +and for the preparation of cream for butter, machines have been +devised which permit large quantities, as thousands of pounds, to be +handled per hour. It is evident under these conditions that the milk +must be heated for only a short time, and hence a higher temperature +must be employed. These machines are called "continuous flow" +pasteurizers since the milk passes through them in a constant +stream. The period of exposure is very short, in some only a few +seconds; hence, they are sometimes called "flash" pasteurizers. + +[Illustration: Fig. 29.--A Continuous Pasteurizer. + +The milk is exposed but a short time since it flows through the +heater in a constant stream.] + +All machines of this type possess the obvious disadvantage that it +is impossible to heat all of the milk for a uniform period. The milk +in contact with the walls of the machine flows much more slowly than +in the middle of the stream, just as the current near the bank is +less rapid than in mid-stream. In none of the machines yet devised +have the designers been able to overcome this disadvantage. In a +test of one of the most widely used pasteurizers of this type, it +was found that some of the milk passed through the machine in 15 +seconds, while the larger part of it was held for about 30 seconds, +and some as long as forty-five to sixty seconds. If the temperature +employed had been such as to destroy the bacteria in that part of +the milk heated for the minimum time, hygienic safety would be +assured, but in order to avoid injuring the physical properties of +the milk, the tendency is to use as low a temperature as possible, +so that the milk heated for the minimum time may often contain +organisms that have passed through the machine uninjured. + +Many devices have been proposed for the heating and cooling of the +milk. In many of the pasteurizers, the milk flows in a thin stream +over a metal surface, on the opposite side of which is the heating +agent, usually steam; while in others, the milk is allowed to flow +through a vat in which revolve a series of discs into which steam is +passed. The discs are of considerable size; thus, making a large +heating surface; the milk is thus heated quickly, and is constantly +stirred by the rotation of the heating discs. In other types the +milk passes into the bottom of a chamber in which a dasher revolves +at a rapid rate. This catches the milk, throwing it in a thin film +onto the wall of the chamber, which is heated with steam on the +opposite side. From such machines, of which the Fjord, the Jensen, +and the Reid machines are types, the milk may be forced to a +considerable height. These are widely used in this country for the +pasteurization of milk and cream for butter making. + +Milk that has been heated must be cooled at once by the use of cold +water and ice. In order to economize in the use of both steam and +cooling agents, the so-called regenerative machines were devised. +The essential feature of these machines lies in the fact that the +cold milk inlet and the hot milk outlet are on opposite sides of a +single partition; thus the inflowing cold milk is partially heated +by means of the already treated hot milk which it is desired to +cool. + +In order to avoid the disadvantages of the continuous machines, +viz., lack of control, an apparatus has recently been devised which +can handle large quantities of milk, heating the same to any +temperature for any desired time. In such a machine the milk is +first heated in a continuous heater, and is then passed into large +tanks in which it is allowed to remain for the desired time, and +from which it flows over the coolers. Such an apparatus is called a +"holding" machine, and is probably the most feasible type of +pasteurizer now on the market, when all factors are considered. In +some of the continuous machines, an attempt is made to accomplish +the same result, by building the machine so that the milk requires +fifteen to twenty minutes for passage through the machine, but in +all such cases the same disadvantage of variation in rate of flow, +as in other continuous flow type of machines obtains. + +=Tests of pasteurizing machines.= It is possible for the operator to +test the rate of flow in a machine, so as to determine whether all +of the milk is heated for a uniform time. This is done most easily +in the following manner: The machine is first filled with water, +heating the same to the desired temperature, and regulating the rate +of flow as it would be if milk was used. The flow of water is then +turned off, and a stream of milk containing a known per cent of fat +admitted to the machine. The time elapsing between the admission of +milk to the machine, and that at which the first sign of turbidity +is noted at the outlet, will be the minimum period necessary for any +portion of the milk to flow through the machine. At frequent +intervals thereafter, samples of the outflowing liquid may be +collected, noting the time at which each sample is taken. The +percentage of fat in the various samples is determined by the +Babcock test; at the moment when all of the water has been removed, +the sample taken will show the same fat content as the milk used. +The samples taken previous to this will show a lower fat test, +dependent upon the relative amount of water and milk. In this +manner, the minimum, the maximum, and the average period of exposure +of milk in the machine tested, can be determined with exactness. + +The accompanying table gives results that were obtained in the +testing of one of the continuous types of machines. The machine in +question required about three hundred pounds of milk to fill it and +was supposed to handle 1,000 pounds per hour. Thus theoretically it +should require twenty minutes for any portion of the milk to pass +through the machine. As will be seen from the data, some of the milk +passed through within seven minutes after the water was shut off and +the milk turned on. The figures also show that not all of the water +had been replaced by the milk in even 45 minutes. In actual practice +like results will be obtained, and a portion of the milk will be +heated to the temperature employed but a short time. In this, the +vegetating bacteria will not be wholly destroyed. + + ========================================================= + Trial | |Per cent of fat in milk coming from + | | machine at following times + |Per cent|--------------------------------------- + | of fat| MINUTES + | in milk|--------------------------------------- + | | 7 | 11 | 15 | 19 | 23 | 27 | 36 | 47 + --------+--------+----+----+----+----+----+----+----+---- + No. I | 4.0 | 0.2| 0.8| 1.6| 2.0| 2.4| 2.6| | + No. II | 3.8 | 0.2| 0.6| 1.5| 1.8| 2.2| 2.6| 3.0| 3.4 + No. III | 3.5 | 0.7| 1.9| 2.4| 2.8| 2.8| 3.0| 3.4| 3.4 + ========================================================= + +=Pasteurization of small quantities of milk.= It is often desirable to +treat a small quantity of milk for home use, in which case the +commercial types of pasteurizers are out of the question. This +treatment can be done in a number of ways, consideration always +being paid to the manner of heating which should be done under such +conditions, as have been shown to be necessary for efficient +pasteurization. Milk may be heated in tall, narrow cans which are +placed in hot water. In the household, milk may be treated by +placing the filled bottle in a pail having a false bottom so the +bottle shall not be broken when the pail is placed on the stove. The +pail should be filled with water so that its level is about the same +as that of the milk. The water is then heated to the desired +temperature, maintained for the requisite period of time, and is +then cooled as rapidly as possible. During the heating, the mouth of +the bottle should be covered, either with an inverted glass tumbler, +or the paper cap may be left in place, simply punching a small hole +through it so as to permit of the insertion of a thermometer. + +[Illustration: Fig. 30.--A Pasteurizer for Use in the Home. + +A milk bottle with a tumbler for a cover. The cover prevents the +formation of the "scalded layer" on the milk during the heating and +also protects the mouth of the bottle from dust.] + +=Efficiency of pasteurizing.= It is easy to destroy over 99 per cent +of the bacteria present by the use of any of the modern types of +machines. The number remaining after treatment will be largely +dependent, other things being equal, upon the number of bacteria +before pasteurization. The pasteurizing process is not one by which +poor milk can be changed into good milk, nor is it legitimate to use +the process in place of cleanliness, as is sometimes done. There is +a legitimate field for the process in the handling of market milk, +as well as in the creamery; but it should be used to improve the +keeping quality, and to insure the freedom of the milk from +pathogenic bacteria, when other protective measures have been +carried as far as possible under the prevailing conditions. + +=Details of process.= If the process is to be successful, due +attention must be given to certain details. In the treatment of +market milk, care should be taken to use only that in which the +acidity has not materially increased. A fair standard is about 0.2 +per cent. High acid milk usually means old milk or dirty milk, +either of which is very likely to contain many more spore-bearing +bacteria than clean, fresh milk. The greater the number of spores, +the more rapidly will the pasteurized milk spoil. If it is possible +to exercise any selection of milk prior to pasteurization, the rapid +test for determination of acidity will prove of great advantage. + +Care should be taken to prevent fluctuations in the temperature to +which the milk is heated. With varying steam pressure and variations +in the rate of flow of milk, these fluctuations may be very +considerable. Regulators are now made that will control the +temperature within narrow limits. + +In all pasteurized milk as it flows from the machine, there will +remain some living bacteria. The spores will not be destroyed by any +pasteurizing process, and under commercial conditions, vegetating +bacteria are also present. If the milk is not quickly chilled after +heating, these forms will grow, and their development is +particularly hastened by the destruction of the lactic bacteria, the +acid of which would otherwise hold them in check. The result is +that, unless immediately chilled, pasteurized milk spoils almost as +rapidly as though it had not been heated at all. Efficient and rapid +cooling are, therefore, as essential a portion of the process as the +heating itself. + +Care should also be taken to protect the milk from contamination +after treatment. Every utensil with which it comes in contact should +be sterilized. The bottles should be thoroughly washed and +sterilized and subsequently protected from dust until used. + +=Sterilization of milk.= It is possible to render milk sterile by the +use of temperatures above the boiling point of water, where it is +heated in a closed vessel, in which steam under pressure is +generated. Such milk is often found in the European markets. In our +own country, the only milk of this kind is the so-called "evaporated +milk." In this process sweet fresh milk is evaporated in vacuum pans +to about one-third of the original volume. This is then placed in +tin cans, which are treated, as in the canning of such vegetables as +peas and corn, by heating the milk to 230° or 240° F. for a few +minutes. In this process, the bacteria (spores as well as vegetating +forms) are completely killed, and the milk acquires a brownish tint, +due to the caramelization of the sugar. The appearance of the +product is very similar to cream, and previous to the passage of +the pure food law, it was sold as evaporated cream. + +Condensed milk is not wholly free from bacteria, but is sufficiently +thick, by reason of its treatment so that the contained bacteria +cannot grow. They remain dormant in the milk, but as soon as it is +diluted to a normal consistency, growth takes place, and the milk +rapidly spoils. Condensed milk is prepared by adding cane sugar to +fresh sweet milk, then evaporating the mixture to one-third the +original volume, forming a semi-solid product. Syrups owe their +keeping qualities to the same factor, as condensed milk, _i.e._, the +high consistency. + +Milk is also preserved by wholly evaporating the water, thus leaving +a dry powder, which on being mixed with water again will have much +the same properties as the original milk. Various methods have been +devised for the preparation of these milk powders, all of which have +been patented by the inventors. If the powder is to be kept for long +periods, skim milk must be used, since the fat slowly undergoes +changes which cause it to have a rancid odor. These dry preparations +are largely used by bakers in place of fresh milk. + + + + +CHAPTER VII. + +BACTERIA AND BUTTER MAKING. + + +In the making of butter it is necessary to concentrate the milk fat +into a small volume. This process, known as creaming, may be +accomplished by gravity, if the milk is allowed to stand +undisturbed, the fat globules rising slowly to the surface. Much +more rapid separation may be secured, by placing the milk in a +rapidly revolving container in which it is subjected to centrifugal +force, which causes the heavier parts of the milk to pass to the +outside of the bowl, while the lighter part, the fat, collects at +the center of the revolving bowl. There is an enormous number of fat +globules in milk, over 5,000,000,000 in each cubic centimeter, and +as these move through the milk serum, they carry with them many of +the bacteria. The cream is thus much richer in bacteria than is the +skim milk, or even the milk before separation. Besides the +mechanical separation in the manner described, the method of +creaming is of importance, in determining not only the number but +also the kind of bacteria in the cream. + +=Methods of creaming.= In the shallow-pan method of creaming, the milk +is kept at ordinary room temperatures. These temperatures favor +especially the growth of the acid-forming bacteria. The milk is +usually sour by the time the cream is removed from it; consequently, +the bacterial content of the cream is high. Moreover, the cream is +exposed to air contamination, and is thus seeded with molds, and +those forms of bacteria that are always found in the air. The cream +obtained in this manner is likely to contain not only numerous +bacteria, but a great variety of forms, some of which undoubtedly +are the cause of the poor keeping qualities of butter made from such +cream. + +In the more modern method of gravity creaming, in which the milk is +placed in deep narrow cans kept in cold water, the conditions are +not favorable for the growth of acid-forming bacteria. If the milk +is produced under clean conditions, and is placed in cold water at +once, the bacterial content of the cream will be low, and it will be +less likely to contain undesirable forms than the cream which is +obtained from the shallow pans. + +In separator cream the bacteria will be represented by the kinds +present in the milk at time of separation. If this milk is quite +old, the cream will contain large numbers of bacteria; if, however, +early separation is made and the milk is clean, the bacterial +content of the cream will be low. + +=Types of butter.= Butter may be divided into two types--acid or +sour-cream, and sweet-cream, depending upon whether the cream is +allowed to undergo the acid fermentation or not before it is +churned. In southern Europe, it is the custom to churn the cream as +sweet as possible, and the resulting product possesses only the +natural, or primary milk flavor. To one accustomed to butter made +from sour or ripened cream, this taste is flat, and if the butter is +free from salt, may remind one of grease. Sweet-cream butter has a +delicate flavor when it is made from good milk, and the taste for it +is rapidly acquired. In some centers, as in Paris, the market +demands this type of butter quite exclusively. + +If the cream is allowed to undergo the acid fermentation before +churning, the butter has a much higher degree of flavor and one that +differs materially in kind. Under primitive methods, it was +difficult to keep the cream sweet until it could be churned. On the +small farm with gravity creaming in shallow vessels and infrequent +churning, the cream was certain to be sour when churned. +Undoubtedly, the making of butter from sour cream came into use +because of its greater convenience; people became accustomed to +sour-cream butter, and at the present time it is used in the greater +part of the world, and is the type made in all of the great dairy +countries. + +=Ripening of cream.= In modern dairy practice the souring of the cream +is called the _ripening_ process, and is, where the best methods are +employed, largely under the control of the butter maker. The changes +that go on in the ripening process are the same as have been +discussed in the acid fermentation of milk. The increase in acid is +accompanied by an enormous increase in the number of bacteria; the +ripe cream will contain hundreds of millions of bacteria in each +cubic centimeter. The effect of this germ life is to improve or +injure the butter, depending upon the class of bacteria to which it +belongs. The problem of the modern butter maker is to control the +kinds of bacteria growing in the cream. + +The temperature at which cream is held during the ripening process +is favorable to the growth of the acid-forming bacteria; hence, in +ripe cream, they are practically the only kind of bacteria to be +found. It must be remembered however, that there are different +classes of acid-forming organisms, some of which produce desirable +flavors, while others are distinctly harmful. + +The intensity of flavor of butter is, in a general way, directly +related to the amount of acid that is formed in the cream. A low +acidity at time of churning is usually associated with a mild +flavor, while a higher degree of acidity, up to a certain point, +imparts a more pronounced flavor to the product. If cream is +over-ripened, the quality of the flavor is seriously impaired. + +In determining the acidity of cream, a definite volume is taken, and +the acidity determined by titration, expressing the results as such +a per cent of lactic acid. Manifestly, the amount of fat in the +cream influences the apparent per cent of acidity. The acidity will +not usually exceed 0.5 to 0.7 per cent, but in reality the serum +will contain more than this, as the acid is formed in the serum, the +butter fat having no role whatever. In a very rich cream, 40 to 50 +per cent fat, it is impossible to develop more than 0.4 to 0.5 per +cent of acidity, and the flavor of the butter will be low, because +of the relation between the amount of acid and fat, while in a thin +cream having the same acidity, the ratio between the amounts of fat +and acid will be very different. For example, in one hundred pounds +of 50 per cent cream of 0.5 per cent acidity there will be one-half +pound of acid and fifty pounds of fat; in the same quantity of cream +containing 20 per cent of fat and having an acidity of 0.5 per cent +there will be one-half pound of acid to twenty pounds of fat. The +flavor of the butter from the rich cream will be quite different in +intensity from that made from the thinner cream. + +The acidity of cream cannot be determined with any degree of +accuracy by the taste or odor. Every butter maker should have some +method of determining the degree of acidity in his cream, so that he +may better control the flavor of his product. Several methods have +been devised for this purpose and the necessary apparatus is sold by +all dairy supply houses. + +The effect of the ripening of the cream is shown not only in the +flavor of the product, but in a number of other ways. Sour cream +churns more easily, and more exhaustively than does sweet cream. It +is supposed that the fat globules are surrounded by a film of +albuminous material which prevents their coalescing readily. During +the ripening process, the action of the acid apparently dissolves +this enveloping substance, and the globules cohere more easily in +the churning process. + +When raw cream is used the ripened-cream butter keeps better than +that made from sweet cream. In sweet cream there are few lactic +bacteria, the majority of the bacteria present being of various +kinds, many of which may be injurious, so far as the keeping quality +is concerned. In sour-cream butter the lactic bacteria make up over +99 per cent of the bacteria present, and their presence tends to +prevent the development of undesirable non-acid forms. + +=Source of butter flavor.= The flavor of ripened-cream butter has been +shown to be directly connected with the acid-fermentation of the +cream. The amount of lactic acid formed from the sugar fermented is +dependent upon the kind of bacteria present. The acid-producing +organisms that are desirable from the standpoint of the butter maker +form comparatively small amounts of other by-products, but these +undoubtedly affect the flavor of the butter. As fats have the power +of absorbing odors, the butter fat absorbs some of the by-products +of the acid fermentation, thus acquiring a certain aroma and +flavor. + +It is not necessary that the cream be ripened, in order to have the +fat acquire a flavor, for if sweet cream is churned with a +considerable proportion of sour milk, the butter will have much the +same flavor, both as to intensity and kind, as though the cream had +been allowed to sour naturally. A process of butter making known as +the LeClair method is based on this principle. The flavor-producing +substances can also be absorbed by the butter after it is churned, +by working the butter in contact with sour milk. Attempts have been +made to add pure lactic acid to the cream, instead of allowing the +acid to be formed by the bacteria, but while the physical effect on +the cream is the same, the flavor and aroma of the butter are +deficient, because the acid itself does not supply the necessary +aromatic products. This emphasizes the importance of the by-products +of the acid fermentation other than the lactic-acid. + +In the past numerous attempts have been made to find organisms that +might be added to the cream, in order to produce the delicate flavor +characteristic of the best type of butter. Some bacteriologists have +claimed that the source of the flavor-giving substance was to be +found in the decomposition products of the nitrogenous constituents +of the milk. None of these attempts have stood the test of practical +use in creameries, and it has been demonstrated that the finest type +of butter can be made by the use of lactic bacteria alone. Formerly, +when butter was made wholly from cream soured under natural +conditions, a much higher degree of flavor was developed. Under +present market demands, a less pronounced flavor is desired, a +condition more readily met by the use of modern methods. + +=Importance of butter flavor.= The importance of flavor in determining +the commercial value of butter is evidenced by the relatively high +value placed upon this factor in scoring, viz., flavor, 45 points; +body or texture, 25 points; color 15; salt 10; and package 5 points. +The factors on which butter is judged, are with the exception of +flavor, wholly under the control of the maker, but as the production +of flavor is dependent on the kind of bacteria present in the cream, +it is a far more difficult matter to control, and yet it is of the +utmost importance in determining the value of the product. + +The flavor of the butter is dependent on the quality of the cream. +If this is dirty and sour, the maker has little control over the +type of fermentation, and hence, little control of the flavor of the +butter. This has led in some cases to the grading of the cream, +basing the division on the acidity, flavor, and fat content. Such +practice is entirely justifiable, as a better quality of butter can +be made from fresh, sweet cream than from that already fermented. It +is noteworthy that the quality of butter has not improved since the +introduction of the centralizer system, in which cream is shipped +for long distances. + +=Control of the type of fermentation.= In the older methods of butter +making, there was little or no control of the type of fermentation +that took place in the cream. Where milk is produced under clean +conditions, and kept at ordinary temperatures, it will generally +undergo fermentation changes, due to the desirable type of +acid-forming organisms. In milk, which is less carefully handled, +the undesirable bacteria are more abundant and the quality of the +butter of lower grade. When butter was made on the farm, before the +development of the factory system, it was not a question of vital +importance whether the product was uniform from day to day, but +with the advent of the modern creamery, turning out thousands of +pounds of butter per day, and with the extension of the markets for +the product, the question of uniformity came to be of much +importance. A uniform product can be secured only by the control of +the type of fermentation in the cream, or by the control of the +kinds of bacteria that cause the souring of the cream. Modern +methods of butter making have been devised on the basis of an +improvement in the ripening process. + +=Starters.= From the earliest practice of allowing the cream to stand +until sufficient quantity had accumulated for churning, it was only +a step, but a most important one, to the addition of sour milk, sour +cream, or butter milk, to hasten the ripening process. This was the +beginning of the modern starter. Experience demonstrated that the +addition of these already fermented liquids exercised a desirable +effect upon the production of butter flavor, even though, at that +time, the phenomenon of milk fermentation was not satisfactorily +understood, and the relation of bacterial by-products to the +production of flavor in butter was not recognized. + +As a result of experience alone, improvements in the development of +the "home made" starter took place. By careful selection of clean +milk, and the natural fermentation of this under carefully +controlled conditions, as well as the control of the temperature of +the cream during the ripening, improvement in the technique of cream +ripening gradually developed. More and more attention was given to +the preparation of the starter, and its propagation from day to day, +under conditions which would prevent its deterioration. This method +of utilizing naturally fermented milk or cream was gradually +extended, until it became almost universal in the larger +butter-producing districts. + +In 1890 a more refined and scientific process was introduced by the +Danish bacteriologist, Storch. Recognizing the fact that butter +flavor was attributable to the development of the bacteria present +in the ripening cream, he conceived the idea of isolating the +various types of organisms found in milk and testing them as to +their effect on the quality of flavor. Selection was then made of +the most favorable flavor-producing types, and these were propagated +in suitable culture media, such as skim milk, which was rendered +more or less perfectly sterile by pasteurization or sterilization. +Under such conditions the addition of a selected ferment could be +made to the fresh cream, and so control the type of fermentation +which occurred therein. An essential requisite in any organism used +for this purpose must be the ability to produce relatively large +amounts of acid rapidly at ordinary ripening temperatures, and also +to form sufficient quantities of the proper flavor-producing +substances to impart a suitable flavor to the butter fat. Such +starters are known as pure culture or commercial starters, and are +prepared in both liquid and dry form. At present they are used to a +greater or less extent in all of the leading dairy districts. + +Liquid starters consist of a mass of sterile nutrient medium, milk +or beef broth, inoculated with the pure culture. The dry starters +are made by adding liquid cultures, containing the growing bacteria, +to some absorbing material, such as milk sugar, milk powder, or +starch, the whole mass being dried at low temperatures, so as not to +injure the bacteria. Under such conditions the bacteria, exist in a +dormant state, and are protected from their own by-products, to +which they would be exposed if maintained in liquid cultures. The +keeping quality, therefore, of dry cultures, is much better than +that of liquid cultures. + +By the use of the pure-culture starters, the butter maker is able to +add to his cream the same kind of bacteria from day to day, and the +butter will be more uniform than when the less constant home-made +starter is employed. In cream to which the starter is added, there +are present a greater or less number of acid-forming bacteria, +depending upon the age of the cream, and upon the condition under +which it was produced. These will grow during the ripening process, +and the flavor of the product will be the result of the mixture of +the bacteria in the cream. The maker can not, therefore, be certain +that the addition of a pure culture to raw cream will effectively +control the type of fermentation. This can be secured only by first +destroying the existing bacteria in the cream, before the selected +culture is added. Heating the cream accomplishes this; and in cream +thus freed from the various kinds of bacteria, the butter maker can +insure the dominance of the desirable types, contained in the +pure-culture starter. If the cream can be obtained in a sweet +condition, the maker through this process of pasteurization, and the +use of pure cultures, secures almost perfect control over the type +of fermentation that occurs in the cream, and thus exercises control +over the degree and kind of flavor of the product. This most +scientific type of butter making is now used by the most progressive +butter makers in the leading butter-producing regions of the world. + +Pasteurization of the cream also distinctly improves the keeping +quality of butter, a condition doubtless due to the freedom of the +same from organisms other than the lactic bacteria. This is a factor +of as much importance as uniformity, because under modern business +conditions, the surplus production must be kept in storage, and it +is essential that the quality should not deteriorate materially +during this time. + +=Process of pasteurization for butter making.= In the pasteurization +of market milk, it is necessary to take into account the effect of +heating on the physical and chemical properties of the milk, and the +degree of heat that can be employed is limited. In pasteurizing +cream for butter, there is no such limitation, and the cream may be +heated to any temperature desired. In Denmark where the process of +pasteurization has been used most extensively, temperatures ranging +from 176° F. to 190° F. are used. The machines are of the +"continuous flow" type, and the cream rather than the whole milk is +treated. To prevent the spread of tuberculosis and other diseases, +the Danish government requires that all cream and milk be heated to +176° F., before the skim milk or butter milk is returned to the +farms. + +The heating of the butter fat to high temperatures has an injurious +effect on the texture of the butter, unless the cream is cooled to +50° F., for a period of at least two hours previous to churning. + +=Propagation of starters.= As has been previously shown, the quality +of butter depends on the kind of bacteria in the cream or in the +starter added. The commercial starters contain lactic acid bacteria +that have been selected with especial care; most of the starters now +sold contain but a single kind of bacteria; hence, are often called +pure-culture starters. The package purchased contains but a small +quantity, and before the starter can be used in the ripening of +cream, it must be increased in amount. It must also be propagated +from day to day so that a fresh starter shall be available daily for +addition to the cream. The propagation of the starter must be done +with especial reference to keeping it in good condition and in as +high a state of purity as possible. + +In the past the starter was propagated, by adding the contents of +the bottle purchased to a small amount of milk that had been heated +and cooled; this, if kept in a warm place, would be curdled in +twenty-four hours, and could be used for the inoculation of a large +mass of milk, that had been treated in a like manner, and which, +when curdled, was added to the cream; a small amount was saved for +the purpose of again inoculating a mass of milk that had been heated +and cooled. Following this method it was very difficult to keep the +culture from becoming contaminated with other forms of bacteria. +More recently the most successful butter makers have propagated the +so-called "mother starters" in small vessels, and have used the +larger mass of starter for the inoculation of the cream alone. + +Glass vessels are preferable for the propagation of the mother +starters since they are impervious and through the transparent wall +the condition of the ripened starter can be more easily determined +than in a metal or earthenware vessel. An ordinary milk bottle with +an inverted tumbler for a cover, to protect the starter from +contamination from the air, is a most convenient vessel. + +The starters may be propagated either in whole or skim milk; the +former is preferable since, in most creameries, it can be more +easily selected. The quality of the milk used has much to do with +the quality of the starter; it should be as fresh and clean as it +is possible to obtain. The clean bottle should be filled half to +two-thirds full, covered and heated in some manner so that the milk +shall be at a temperature close to the boiling point for fifteen to +twenty minutes. The heating may be done by placing the bottles in +water, which is heated on a stove or by steam, or the bottles may be +subjected to streaming steam. The milk is cooled quickly and the +contents of the package purchased added and well mixed with the +milk. In the case of the dry starters, the mixing should be done +with especial care. The bottle is kept in a warm place and in +twenty-four to thirty-six hours, the milk should be curdled. A +second bottle must be treated as before and inoculated from the +first, and the process repeated daily since the bacteria must have +fresh food, if they are to be maintained in good condition. + +In order to accomplish this, the maker must be able to maintain +constant conditions from day to day, especially with reference to +the amount of the ripened starter that is transferred to the fresh +bottle of milk, and the temperature at which the bottles are kept. A +spoon, arranged as shown in Fig. 31, enables one to carry a definite +amount of the ripened starter to the bottle of milk to be inoculated +and a constant temperature box (Fig. 32) permits of the maintenance +of the same temperature from day to day. Through careful supervision +of these points, and by taking care at every step to avoid the +introduction of contaminating organisms, the purity of the culture +can be maintained, and the bacteria kept in a healthy condition. + +The starter is used because of the acid-forming bacteria it +contains; it is said to be ripe and in the best condition for use at +the time it contains the greatest number of living bacteria. It +has been found by experiment that this is at the time the milk +curdles at ordinary temperature, or when the acidity is about +0.6-0.7 per cent. If the acidity is allowed to increase to 0.8 or +0.9 per cent, the number of bacteria will be less and a larger +amount of the starter must be used in order to ripen a definite +amount of cream in the desired time. The use of an overripe starter +may also have an injurious effect on the flavor. + +[Illustration: Fig. 31.--Bottle for Mother Starters. + +A milk bottle with a tumbler for a cover and a spoon for inoculating +the other bottles enables the butter maker to propagate the starters +without contamination.] + +The ripened starter should be perfectly homogeneous, showing no +bubbles of gas or free whey; the odor should be agreeable and the +acid taste mild; on shaking, the curd should break up into a smooth, +creamy liquid free from lumps. This is especially important in the +starter that is to be added to the cream, since otherwise the +starter cannot be uniformly mixed with it and white specks of +curdled casein will be noted in the butter. + +[Illustration: Fig. 32.--An Incubating Chamber for Starters. + +The inner compartment will hold a pail of water and the bottles for +the mother starters. The temperature can be kept at any desired +point by the use of warm or cold water. The four-inch space between +the walls is filled with hay or mineral wool.] + +The firmness of the curd is not so dependent on the amount of acid +formed as upon other factors. If the curd shrinks to any extent and +the whey is expressed, it is certain to produce a starter that will +contain lumps that cannot be broken up. With a pure culture of +lactic bacteria, there is little difficulty in this regard, but as +soon as gas-forming bacteria are introduced, trouble is likely to +result. + +In the propagation of starters, it is always to be remembered that +the bacteria, although invisible to the eye, are living things, and +unless conditions are favorable in every particular, it is +impossible to keep them in a healthy condition, so that growth in +the cream is rapid, producing the acid demanded for churning, and +imparting to the butter the desired flavor, both as to degree and +kind. No part of the daily routine of the butter maker should be +performed with more care than the preparation of the starters, both +the mother starters, and the larger one for addition to the cream. +The latter can best be made in one of the many forms of starter cans +now on the market, since by their use, the maker can heat and cool +the milk with little trouble, and can maintain the starter at any +desired temperature. Better starters cannot be made in them than by +the use of simple and improvised apparatus, but better results can +be obtained with the same expenditure of time and labor. + +In the handling of the large starter, care should be used not to +overripen, since the larger quantity is more likely to "whey off" +than is the smaller starter. Skim milk rather than whole should be +used for this. It should be selected with care and heated to 200° F. +for thirty minutes. When it is impossible to secure fresh milk for +starter making purposes, either condensed skim milk or milk powder +may be used. The condensed milk is diluted with water until its +volume is about the same as the milk before concentration; the +mixture is then treated the same as fresh milk, being heated and +cooled before inoculation. In the case of milk powder, one part of +the powder is added to ten or twelve parts of water, allowed to +dissolve as far as possible, and the mixture heated and cooled. +Either of these liquids will give satisfactory starters; the cost +however is high, and in most places milk can be obtained more +cheaply. The inoculation and the temperature should be so +controlled, as to ripen the starter at the time it is to be needed. +These conditions must be determined by the maker for himself. It +should be remembered that the bacteria grow much more rapidly, as +the temperature is increased; and hence, the amount of inoculation +is dependent on the temperature at which the starter is to be kept. + +When the starter is propagated under practical conditions, it sooner +or later deteriorates, either in acid production, or in flavor, and +a new pure culture must be procured from the manufacturer. It is +impossible to give a hard and fast rule as to the length of time a +starter can be kept in good condition. It will depend on how well +the maker satisfies the conditions necessary for maintaining its +purity and strength. The use of imperfectly sterilized milk, or +dirty utensils soon contaminates it; overripening is likely to +injure the flavor. One of the most frequent troubles encountered is +the appearance of a slimy or ropy condition in the starter, although +the acidity developed may be normal and the flavor desirable. It has +been found that this condition is not necessarily due to +contamination, as was considered true in the past, but rather to +some change in the lactic bacteria themselves. If the propagation is +continued, the slimy condition will often disappear. + +=Starters in "process" butter and oleomargarine.= The advance which +has recently been made in the science and practice of cream ripening +and butter production is utilized most effectively in the treatment +of cream in the renovating process. Old, soured, and stale cream +is reduced in acidity by the addition of lime. The cream is then +pasteurized and aerated to expel the odors as much as possible. A +large amount of starter is then added and the cream immediately +churned. Under these conditions, the bad flavors are materially +reduced in intensity, and desirable flavors absorbed by the fat from +the selected starter used. It is thus possible to produce butter of +good quality from cream that would at first be regarded as quite +unsuitable for butter production. + +In the manufacture of oleomargarine the same principle is utilized. +The butter aroma and flavor is imparted to the neutral oils and +tasteless fats by mixing the same with a properly prepared starter. +Renovated or process butter is given a desirable flavor in the same +way. + +=Wash water.= It has been found that the purity of the water used in +washing the granular butter has a marked influence on the keeping +quality. If the water is from a shallow well into which surface +water finds its way, it is certain to contain large numbers of those +types of bacteria that are found in the soil, while if it comes from +a deep well that is properly protected from surface contamination, +the bacterial content of the water will be low and no injurious +effect on the butter will be noted. When it is impossible to obtain +pure water for washing purposes, a proper supply may be secured by +sterilizing the water. The most convenient way of heating the water +is by the direct injection of steam. It is necessary to use that +coming directly from the boilers and not the exhaust from the +engine, since the latter is likely to contain small amounts of oil +that will impart to the butter an objectionable flavor. After +cooling, the water is ready for use. It has been shown that the +cost of treating an impure water is more than covered by the +increased returns from the product. + +A pure and healthful water supply should be one of the essential +things of every dairy, creamery, and cheese factory, not only for +the sake of the quality of the product, but also to avoid +contamination of products with disease-producing bacteria. + +=Bacteria in butter.= The germ content of butter will depend on the +type of cream. Sweet-cream butter contains but few bacteria. In +sour-cream butter the content in bacteria will be greatly increased, +especially as to lactic organisms. Often, it may amount to several +millions of organisms per gram. The germ content of butter is said +to be greater on the outside of a package than within the mass, due +doubtless to the free access of air, thus favoring the growth of the +aerobic forms. + +The composition of normal butter does not favor the growth of the +majority of kinds of bacteria that are contained in it. The washing +process removes much of the material suitable as food for the +bacteria, such as sugar and albumen. If considerable butter milk is +left in the butter, the growth of bacteria will be quite rapid, at +first, but does not continue for any considerable length of time. +The addition of salt also tends to restrain the growth of most kinds +of bacteria. + +Butter is at its best when it is perfectly fresh. Deterioration +begins within a short time and the rapidity with which the changes +go on is dependent on the temperature at which the butter is stored. +The temperature of the butter rooms in the large cold storage plants +is kept below 0° F. The butter in such rooms will deteriorate very +slowly, but on removal from the cold rooms and in storage at +ordinary temperatures deterioration goes on more rapidly than would +have been the case when the butter was fresh. At the temperature of +an ordinary refrigerator the changes go on much more rapidly. This +fact has often been looked on as indicating that the factors causing +the changes are biological ones. The influence of temperature in +accelerating the changes would be the same if no biological factor +were active. + +That biological factors are of importance is indicated by the fact +that the keeping quality of the product is profoundly affected by +the quality of the cream. Butter made from sweet, fresh cream, that +has been thoroughly pasteurized, has the best keeping quality, while +butter made from such cream, but not pasteurized, has the poorest +keeping quality, especially when no salt is added. Every process by +which the desirable lactic bacteria are increased in proportion to +other kinds has a marked effect in enhancing the keeping quality of +the butter. Thus, the use of pure cultures in raw cream, and +pasteurization together with the pure cultures, have a marked +beneficial effect. + +The addition of preservatives exerts an effect on keeping quality. +Borax is the chemical most frequently employed for this purpose. Its +use is allowed in Australia and New Zealand in butter that is +shipped to England, but the use of all preservatives is forbidden in +the United States. + +The size of the package also has an effect on the keeping quality; +the smaller the package, the greater is the surface exposed to the +air and the more rapidly the butter deteriorates. Butter used in the +United States Navy is packed in hermetically sealed cans so as to +exclude the air as far as possible. + +From the fact that any condition which restrains or inhibits the +growth of micro-organisms has a tendency to improve the keeping +quality of butter, it would appear that the detrimental changes in +the quality of butter are due to biological causes. The most common +defect known is that usually referred to as rancidity. There are, +however, different types of changes that are probably included under +this head and it is very probable that different causes are +operative in their production. True rancidity is probably due to +biological causes; the so-called tallowy change, in which the butter +acquires the odor of tallow is probably due to the combined action +of light and air on the fat. + +=Bacterial defects in butter.= There are a number of defects in butter +that are positively known to be due to the growth of bacteria in the +milk or cream, or in the butter itself. The lack of flavor is looked +upon as a defect in the case of ripened-cream butter. It may be due +to insufficient ripening of the cream, or to the lack of +acid-forming bacteria that produce the desirable flavor-forming +compounds. Not all acid-forming bacteria are able to produce +favorable, flavor-giving compounds; hence, sour cream butter may +sometimes be deficient in flavor by reason of this fact. + +=Putrid butter.= This specific butter trouble has been observed in +Denmark, where it was first studied by Jensen. Butter affected by it +rapidly acquires a peculiar putrid odor that ruins it for table use. +Sometimes this flavor may be developed in the cream previous to +churning. It may be caused by a number of bacteria. + +=Turnip flavored butter.= Butter sometimes acquires a flavor +resembling turnips. This trouble may be due to the feeding of such +roots, the aromatic substances peculiar to them being absorbed +directly by the milk and thus transferred to the butter. Weigmann +traced a similar flavor to certain bacteria that entered the milk +from barn filth. + +=Cowy odor in butter.= There is sometimes to be noted an odor in +butter as in milk that resembles that of the cow stable. Usually +this defect has been ascribed to the absorption of these odors +directly by the milk. Organisms have also been described that impart +to the butter a very similar odor. Bitter butter may be due to the +feed that is consumed by the cow, or it may be due to those forms of +bacteria that produce a bitter fermentation of the milk. + +=Other abnormal flavors.= Among the numerous abnormal flavors that +have been noted in butter is one of quite frequent appearance, the +so called "fishy" flavor. It is now believed by many that this +flavor is due to the presence of small amounts of iron or copper +salts that have been introduced into the milk from utensils from +which the protective coating of tin has been worn. If the milk or +cream stored in such utensils develops any marked degree of acidity, +the acid will dissolve a small amount of the iron or copper. The +fishy flavor has not been found in sweet-cream butter as would be +expected from the above explanation. In fresh butter a metallic +taste is sometimes present. It is believed by some that on storage +this flavor changes to the fishy flavor. + +All utensils used for the storage of milk and cream should be kept +in good condition so as to prevent the acid milk or cream from +coming in contact with iron or copper. + +[Illustration: Fig. 33.--Moldy Butter. + +The mold grows on the paper in which the butter is wrapped rather +than on the butter. The print on the left was wrapped in the same +paper as the print on the right except that the parchment cover had +been steamed for a few moments.] + +=Moldy butter.= A defect that causes a great amount of loss is the +development of mold on the surface of the butter, either in tubs +or in prints. This trouble is easily prevented. Butter is not well +suited to the growth of mold, but the paper used for lining the +tubs, or wrapping the prints is an excellent medium for mold growth. +The wood of the tub also furnishes ample food for this type of life, +especially where the wood contains any sap. One other essential +condition for mold growth is a supply of oxygen. The mold spores are +widely disseminated, and are always to be found on the butter tubs +and on the paper. The number is not likely to be sufficient to cause +trouble unless the tubs and paper have been kept under such +conditions, as to allow growth to take place on them before use. +During damp, hot weather, the amount of moisture absorbed by these +materials is often sufficient to allow molds to grow on them. This +trouble can be prevented by the storage of tubs and paper in a clean +dry place, or by a disinfecting treatment which will destroy the +mold spores. The most successful method of treatment of tubs is to +apply paraffin to the inner surface, which can be easily done by the +use of some one of the various machines now on the market. The +thin layer of paraffin excludes the moisture from the wood, and also +prevents the mold from obtaining a supply of oxygen for its growth. +The tubs may be steamed, treated with hot water, or filled with a +dilute solution of formaldehyde, and allowed to stand overnight. +Soaking in brine as is usually done in the creameries is of some +effect, but will not completely kill mold spores. + +[Illustration: Fig. 34.--Moldy Butter. + +The butter was placed in a paraffined tub, but the paper was not +treated so as to destroy the mold spores thereon.] + +Butter may mold where the tubs have been thoroughly treated, because +of the mold spores on the paper used for the lining. One of the +black molds is able to thrive on parchment paper whenever the air is +damp. In the past but little attention has been paid to the paper as +a source of trouble. It is certain that it is often at fault, and +that as much attention should be paid to the paper as to the tub. A +most efficient way of treating paper, either for tub liners or print +wrappers is to place same in boiling water for a few minutes. + + + + +CHAPTER VIII. + +BACTERIA AND CHEESE MAKING. + + +Butter, such as that of the sweet-cream type that is highly esteemed +in many parts of the world, may be made without the aid of bacteria, +but no important kind of cheese can be made under commercial +conditions without them. + +=Types of cheese.= Cheese consists of the fat and the precipitated +casein of milk, together with a large amount of water and the salts +found in milk. The numerous types of cheese may be divided into two +groups, depending on the manner in which the curdling of the milk is +brought about. Sour-milk cheese is made from curd, formed as a +result of the acid fermentation of the milk. Thus, at the very first +stage in the making of this type, the importance of bacteria is +apparent. + +The second type is that made from curd, which is precipitated by the +addition of rennet to the milk. This type may also be divided into +two groups, depending upon their texture; the hard cheese, and the +soft cheese. The ordinary cheddar, the common American type, is the +most important example of the hard cheese; Limburger, of the soft +cheese. Cheese are designated as hard or soft, depending upon the +amount of whey that is retained in them during the making process. +The moisture content has an important influence on the type and +amount of life that develops on and in the curd mass, and as will be +seen, the ripening and flavor of the cheese are dependent upon these +biological factors. + +The two groups of hard and soft cheese have no sharply defined +limits, but merge into each other. The extreme types of the hard +cheese are so dry and firm that they can be cut only with +difficulty. Such cheese are used primarily as condiments to impart a +flavor to certain dishes, as macaroni, and for this purpose are +grated. The extreme type of soft cheese is a soft, pasty mass and +can be easily spread with a knife. + +Hard cheese, because the ripening process goes on uniformly +throughout the entire mass of cheese, may be made of any size which +permits of commercial handling. They can also be kept for long +periods and preserve their good qualities. Soft cheese are made in +small sizes, since on account of their consistency, they could not +otherwise be handled, and also because of the manner of ripening. +The ripening is due to the action of organisms developing on the +surface, the by-products of which diffuse into the curd. If the +cheese are too large, the outer layers become overripe, while the +interior remains more or less unchanged, or insufficiently changed. +Soft cheese mature much more rapidly than hard cheese; consequently +they are short lived. + +Although made from the same substance, milk, it is noteworthy that +there are over four hundred varieties of cheese produced. Most of +these find only a local market where made. Less than a dozen +varieties are to be regarded as general articles of commerce. + +=Quality of milk.= In the making of butter there are a number of +processes that the maker can use when he finds himself obliged to +utilize poor milk. The milk can be pasteurized and the harmful +bacteria thus destroyed; desirable kinds can then be added in the +form of a pure-culture starter. Pasteurization also drives off some +of the volatile by-products of the first acid fermentation. By the +use of these means, the maker can prepare a very good product from +poor material. + +In the making of most kinds of cheese, especially those of the +greatest commercial importance, the cheese maker can call to his +help no such aids, but must use the milk as it is brought to him. It +is possible to prepare certain kinds of soft cheese from pasteurized +milk that differ in no essential point from the same cheese made +from raw milk. Hard cheese are also made from pasteurized milk, but +in most cases such cheese differ, especially in the degree of +flavor, from that made from unheated milk. It is quite probable +that, as the factors concerned in the ripening of cheese become +better known, methods will be evolved for the successful production +of many kinds of cheese from pasteurized milk. + +It has been shown that the quality of milk is almost wholly +dependent upon the number and kinds of bacteria it contains. These +bacteria pass into the cheese, and there produce the same products +as they would have done in the milk itself. In butter making, +practically all processes are under the control of the maker, until +the product is ready for the market; but cheese, on the other hand, +passes through a complicated series of changes after it has left the +maker's control. During the manipulation of the milk and the curd in +the vat, he can exert some influence on the quality of the product, +but he is much more dependent on the quality of the milk than is the +case in butter making. + +Every effort should therefore be made to furnish to the cheese maker +the quality of milk from which he can prepare fine cheese. In other +words, the milk should be produced under clean conditions and +carefully cooled and handled until delivered to the maker. Poor milk +from a single farm may have such an effect upon the cheese made from +the milk of twenty farms as to depreciate the selling value of the +entire product several cents per pound. + +The tests that have been previously described (p. 105) have been +devised especially for testing the quality of the milk for cheese +making purposes, and are of the greatest service to the maker in +tracing the source of poor milk. + +=Cheddar cheese.= The first step in the making of cheddar cheese is +the "ripening" of the milk, or the development of a small amount of +acid. In this fermentation, the development of acid is preceded by +an enormous increase in the number of acid-forming bacteria. Milk +for cheese making should show an acidity of about 0.2 per cent or +slightly more than in fresh milk. In other words, the maker wishes +the milk to be in such condition, bacteriologically, that if kept at +a temperature favorable for the growth of the acid-forming bacteria, +the acidity will increase rapidly. + +The curdling of the milk to precipitate the cheese solids is +produced by the addition of rennet, which is obtained by extracting +the fourth stomach of the young calf with a solution of common salt. +In the past the maker prepared his own rennet solution from the +dried stomachs ("rennets"), but at present, the extract is prepared +commercially, in a much more uniform manner. The rapidity of the +curdling is dependent upon the acidity of the milk. In order to +secure proper rennet action, a slight increase of acid over that +found in fresh milk is usually necessary; thus at the very beginning +of the process of making cheddar cheese, the bacteria are of +importance. + +As the milk curdles, the bacteria are enclosed in the curd as are +the fat globules. The curd is cut into small fragments by means of +a curd knife, and as the mass is warmed, the acid develops, causing +the curd particles to shrink, thus expressing the whey. Within a +short time, the volume of the curd is not more than one-eighth that +of the milk, but in the curd are held over 75 per cent of the +bacteria of the milk. To secure rapid curdling in the vat, the milk +is warmed to 85° to 90° F., a temperature that is most favorable for +the growth of the lactic bacteria. Since there is a large number of +bacteria concentrated in a small volume, and the temperature, as +well as all other conditions, is favorable to growth, multiplication +of the bacteria goes on rapidly, and as a consequence, acid is +formed in large amounts, as is shown by the following figures given +by Publow for the manufacture of the export type of cheddar cheese: + + Acidity of milk before adding rennet .2 to .21 per cent + Acidity of whey before heating curd .14 to .145 " + Acidity of whey before removing from curd .16 to .18 " + Acidity of whey coming from the curd after + removal of whey and curd is packed .24 to .30 " + Acidity of whey coming from curd before milling .65 to .75 " + Acidity of whey coming from curd before salting .90 to 1.10 " + +If the milk had been kept at the same temperature as the curd, the +acidity would have increased much more slowly since the acid would +have been distributed through a larger volume. In the cheese curd +the same amount of acid is probably formed, as would have been +produced in the total amount of milk during the same interval. + +The acid produced by this bacterial activity has a most marked +effect on the curd. At first the curd masses are tough and firm, +the particles showing no tendency to adhere to each other. As the +acid increases in amount, the curd becomes plastic, the outer +surface of the particles adhering or "matting," as the maker +expresses it. The result is a solid coalescent mass of curd, which +is cut into small pieces, _i.e._, "milled," before it is put to +press. The acid allows the blending of the pieces under the +influence of the pressure so that a cheese is one single mass. Under +certain abnormal conditions, the development of acid may be +interfered with and the particles of curd fail to mat, in which +case, the cheese will be crumbly when it is cut. The determination +of the proper time for pressing is made by the application of what +is known as the hot iron test. This is made by determining the +length of the "strings" or "threads" which can be drawn from a mass +of curd when it is brought in contact with a hot iron at a cherry +red heat, the length of the curd threads being a measure of the +amount of acid that has been formed in the curd. + +The rate of acid formation within the curd particles is also +measured by determining the acidity of the whey as it comes from the +curd at different stages in the making. This test, which is often +used in place of the "hot iron" test is carried out in the same +manner, as in determining the acidity of milk or cream. The quality +of the cheese, both as to texture and flavor, is dependent to a +great degree upon the amount of acid that is formed during the +various stages in making; hence, the successful maker must follow +closely by some means the acid formation in the curd until it is put +to press. + +It is very necessary that the milk shall contain a sufficient number +of acid-forming bacteria to produce the required amount of acid. If +a sufficient number of bacteria are not present in the milk as it is +received, as is the case with very sweet milk, they must be added +by the maker in the form of a starter, or the process of making will +be much prolonged. + +[Illustration: Fig. 35.--Bacteria in Cheese. + +A photomicrograph of curd just after curdling has taken place. Note +the few lactic acid bacteria embedded in the curd.] + +=Starters in cheese making.= The starters used in cheese making, are +identical with those employed in butter making and the same +precautions should be observed in their propagation. It is important +that the starters should not be such as to form a hard curd that +cannot be mixed uniformly with the milk, since the curd particles +would appear as white specks in the cheese. The starter should be +added to the milk through a hair sieve, and well mixed with the +milk, so as to distribute the bacteria uniformly. Amounts varying +from 0.5 to 2 per cent are used. In butter making, it is essential +that the bacteria of the starter be able to form not only acid, but +sufficient flavor-forming substances to impart to the butter a +desirable flavor. In cheese making it is not probable that this +latter characteristic is of any particular importance. + +[Illustration: Fig. 36.--Bacteria in Cheese. + +A photomicrograph of curd at the time the salt is added. The lactic +acid bacteria have increased materially in numbers.] + +It is desirable that the process of cheese making shall conform as +closely as possible to that which experience has shown to give the +best results. The rate at which acid is developed in the curd and +the rapidity with which the whey is expelled therefrom should bear a +certain ratio to each other. If the milk has too high a degree of +acidity, _i.e._, is overripe, the acidity developed in the curd will +be too high before the curd is sufficiently firm; with a very sweet +milk, the reverse may be true. It is desirable for the cheesemaker +to obtain as good an idea as possible of the condition of the milk +with reference to its bacterial content, since this will determine +the rate at which acid will be formed in the curd. If the milk is +too sweet, _i.e._, too low in acid-forming bacteria, a starter +should be added. The only methods by which this information can be +obtained by the maker is by determining the acidity by the usual +method or better by the use of the rennet test by which is +ascertained the time required for a given amount of rennet to curdle +a definite quantity of milk at a standard temperature. The varying +factor in the test will be the acidity of the milk. Very slight +differences influence profoundly the time of curdling. If, working +under standard conditions, it is found that the time of curdling of +one sample is 10 seconds and of another sample, 20 seconds, it is +proof that the acidity of the first is higher than that of the +second, that its bacterial content is greater and that acidity will +develop in the curd more rapidly. The first may need a small amount +of starter, the second a larger quantity. Working with milk from the +same source, the maker, from his experience, will know how much +starter should be added to milk that has given a certain result with +the rennet test in order that the acid shall be developed in the +curd at a desired rate. + +=Ripening of cheese.= The curd at the time it is put to press is tough +and rubbery, and has none of the characteristic flavor of cheddar +cheese; it is also quite insoluble and indigestible. Before the +cheese is fit to eat it must pass through a complex series of +changes which are collectively known as _ripening_. In these changes +there is not only a breaking down of the casein into soluble +compounds, which process makes the cheese soft and plastic under +pressure, but the characteristic flavor is developed in greater or +less degree. A very considerable part of the cheese thus becomes +soluble in water, and it is much more easily digested than in an +unripened condition. + +The different factors that are operative in the ripening changes are +not yet fully known, but in recent years as a result of scientific +study, material progress in the study of the changes has been made. + +=Rennet.= The commercial rennet extract when in condition for use +contains very few bacteria. A preservative, boric acid, is added by +the manufacturer to restrain the bacteria, otherwise the extract +would soon be unfit for use. The bacteria in the commercial rennet +extract are too few to be of any importance whatever in the ripening +process. + +Rennet extract contains an enzyme, rennin, that causes the milk to +curdle; also another enzyme, pepsin, that exerts a digestive action +on the curdled casein. Pepsin is always found in the stomach juices +of all animals, but no digestive action takes place, unless the +reaction is distinctly acid, as is the ease under normal conditions, +since hydrochloric acid is excreted by the walls of the stomach. +Outside of the stomach, the same conditions must obtain with +reference to the presence of acid, if pepsin is to exert a digestive +effect. In the cheese curd, the milk sugar is rapidly changed into +lactic acid by the action of the bacteria. This gives the proper +chemical reaction for peptic action, and the enzyme is then able to +act on the paracasein, the nitrogenous part of the cheese. If milk +contains no acid-forming bacteria, conditions will not permit of +peptic action, and as a consequence, the ripening processes do not +take place. If the sugar is fermented by some organism that does +not form acid, as the lactose-fermenting yeasts, the cheese does not +ripen. The lactic bacteria are therefore an essential factor in +inaugurating the ripening changes in all types of rennet cheese. + +=Preservative action of acid.= In a previous chapter it was shown that +raw milk does not undergo putrefaction because of the restraining +effect of the acid formed by the lactic bacteria on the putrefactive +organisms. This same phenomenon is noted in cheese. Milk always +contains putrefactive bacteria which pass into the cheese, but they +cannot grow therein because of the high acidity. In the absence of +the acid-forming organisms in the cheese, the cheese may remain +tough and rubbery, on account of the lack of suitable conditions for +the action of the pepsin of the rennet extract, or when the milk +contains large numbers of digesting organisms, the cheese may +develop a putrefactive condition, as noted by the offensive odor and +soft pasty texture. + +=Other factors concerned in cheese ripening.= There are other factors +that are also concerned in the complex series of ripening changes +noted in cheddar cheese. All animal fluids and tissues, if kept +under perfectly sterile conditions at ordinary temperatures, will +undergo a certain amount of decomposition, due apparently to their +content in enzymes that have a digestive action. Meat kept in +storage becomes more tender due to the softening of the connective +tissue. Milk, derived as it is from actively secreting cell tissue, +gives certain reactions that are common to living material. If +chloroform, which restrains the action of bacteria, but does not +prevent the activity of enzymes, is added to it, it will curdle in +the course of a few weeks and will become partially digested. This +digesting ferment found in milk is known as _galactase_. Compounds +are formed in milk thus preserved that are similar to those found in +a ripe cheddar cheese. Many experiments have been made with +pasteurized milk, but it has not been possible to produce typical, +normal cheese from thoroughly pasteurized milk. Such cheese are +markedly deficient in the typical flavor of cheddar cheese. From +this fact it is believed that the inherent enzymes of milk are a +factor of some importance in the ripening of this type of cheese at +least, if not of all types. + +In the past, other factors have been thought to be of importance. +Duclaux, a French bacteriologist, considered that the enzymes formed +by the digesting bacteria are responsible for the ripening. It is +now known that they can have but little if any part in the process, +since they are not present in all cheese in sufficient numbers to +have any marked effect, and since the acidity of the cheese mass +will not permit of their development. + +Other types of bacteria have been considered by bacteriologists to +be of importance in the ripening process, but it is certain that the +purely digestive change in the mass of the cheese can be accounted +for through the action of the factors already noted. + +=Flavor production.= The flavor of any type of cheese is the most +important characteristic, just as it is in butter, for it is largely +the flavor that determines the selling value of the product, and is +the most difficult thing to control. It has been thought that the +flavor-producing substances were derived from the paracasein of the +curd and were produced by the factors that are concerned in the +digestion of the paracasein. It has been shown that a cheese may be +thoroughly ripened as far as its physical properties are concerned; +that it may contain the end products of casein digestion, and yet +be low in flavor. From recent researches it seems probable that the +production of flavor is connected with the change that the sugar +undergoes in the acid fermentation, as volatile acids, acetic, +formic, etc., as well as alcohols and esters are formed in +increasing amounts as the ripening progresses. These may have come +from the decomposition of the milk sugar, or from a secondary change +in the products of the lactic fermentation. There are organisms in +both milk and cheese that do not grow on the ordinary culture media +used by the bacteriologist, and it may well be that some of these +are of importance in flavor production. Their destruction in +pasteurization is likely to be one of the reasons for the failure of +cheese made from pasteurized milk to develop typical flavor. + +=Effect of temperature on ripening.= The temperature at which the +ripening cheese is kept has been found to be of the greatest +importance in determining the quality of the product. If the cheese +is kept at high temperatures, the ripening proceeds rapidly; the +cheese is short lived, and has a sharp, strong flavor, and generally +a more or less open texture. Unless the cheese is made from the best +quality of milk, it is likely to undergo undesirable fermentations +when ripened at high temperatures. + +Within recent years it has been found possible to ripen cheese at +temperatures that were previously thought to be certain to spoil the +product. Much of the cheese is now ripened at temperatures below 50° +F. The ripening goes on more slowly than at higher temperatures, but +the flavor of the cheese is clean and entirely devoid of the sharp +undesirable tang that is so frequently noted in old cheese, and the +texture is solid and meaty. Ripening at low temperatures, when the +milk is not of the best quality, is certain to result in a much +better product than when higher temperatures are employed. + +=Abnormal fermentations in cheese.= As has been previously shown, it +is necessary to have an abundant supply of acid-forming bacteria in +the milk from which cheese is to be made. If these bacteria are +supplanted by other kinds, the product will be more or less abnormal +either in texture or in flavor, or possibly in both. Many of these +abnormal fermentations have been studied and the organisms concerned +in the changes found. + +If the milk is handled carelessly, it will contain many bacteria +able to form acid and gas. As noted previously, these organisms form +products in milk that have an offensive odor and a disagreeable +taste. In cheese the gases cause the formation of holes, more or +less numerous, depending on the number of the gas-forming bacteria +in the milk. Where these bacteria are abundant, gas may appear while +the curd is in the vat, causing it to float in the whey, when it is +known as a "floater." Again, the gas may not become evident until +the cheese is in the press or on the curing shelf, when it becomes +apparent by the swelling or bulging of the cheese. Such cheese is +termed "huffed" or "swelled." The internal pressure may be so great +as to cause the cheese to crack and to force out some of the curd. +The presence of gas holes is indicative of a poor cheese, because +the formation of gas is always accompanied by the presence of other +undesirable compounds. + +Pure culture starters are often used to overcome gassy +fermentations. In cheese a certain amount of acid can be produced by +the acid-forming bacteria. When the pure lactic bacteria alone are +present, the cheese is very likely to be of good quality. If the +sugar is fermented by gas-forming organisms, the curd will be full +of holes and the flavor poor, while if the sugar is fermented by a +mixture of the desirable and undesirable bacteria, the quality of +the product will depend on the relation of the two types. If through +the addition of a pure-culture starter, the proportion of desirable +bacteria is increased, the gas will be lessened in amount and the +cheese improved. It was formerly supposed that the lactic bacteria +had an injurious effect on the gas-forming organisms. There is no +good reason to believe that this is the case, but that both grow in +the milk and cheese, but since only a certain amount of acid can be +produced, it is important to have as much of it formed by the lactic +bacteria as possible, since the amount of injurious products in the +cheese will thus be limited. + +[Illustration: Fig. 37.--Gassy Cheese. + +Such a cheese is worthless on account of its poor flavor. The +irregular holes are mechanical. The crack on the upper side is due +to the pressure of the gas which has caused the cheese to bulge at +this point.] + +The gas formed in the curd before the cheese is put to press can be +gotten rid of by proper manipulation of the curd. While this +treatment may improve the appearance of the cheese, it does not +eliminate the substances that impart to the cheese undesirable +qualities. + +Gassy curds have also been treated by washing the curd with cold +water. Care must be taken in applying this method for the removal of +too much of the sugar and acid from the curd by the washing will +permit the growth of injurious forms of bacteria. The addition of +salt or of saltpeter has also been made to the milk in order to +overcome gassy conditions in the milk. In the handling of gassy +milk, the usual practice has been to develop a larger amount of acid +before drawing the whey than in the case of good milk. This was done +with the idea that acid suppressed gas formation. It has been shown +previously that this is not the case. It has also been shown by +Doane that the development of too much acid before drawing the whey +is likely to result in undesirable flavors, producing what is known +as "high-acid" or "sour" cheese. + +The gas-forming bacteria grow best at high temperatures; hence, +cheese kept under these conditions are more likely to be affected by +this trouble than are those kept at lower temperatures. + +The most successful method of preventing trouble with gassy milk in +cheese making is to eliminate undesirable milk by frequent testing +of the supply of the different patrons by means of the Wisconsin +curd test. + +Not only gas-forming bacteria may be the cause of gassy cheese, but +the lactose-fermenting yeasts may cause similar trouble. If these +are abundant in the milk, a considerable part of the sugar may be +fermented by them, in which case, carbon dioxide gas is abundantly +formed. The cheese thus rendered gassy will present the same +appearance to the eye as where the gas is formed by bacteria, but +will have a different flavor. The odor of alcohol may be evident, +and if most of the sugar has been fermented by the yeast, the +acidity of the cheese may not be sufficient for the pepsin to exert +its digestive action. + +Milk containing many gas-forming bacteria occurs most frequently in +summer. It is claimed by some that the milk of cattle pastured on +low lands is more likely to contain the gas-forming organisms than +that from cattle running on higher lands. If this is true, it must +be due to the bacterial content of the soil; the udders of the +animals become soiled as they lie on the ground, and during the +milking, the dust finds its way into the pail. Many cheese makers +think that the milk from an animal suffering from a garget may be +the cause of the huffing of cheese. This belief is undoubtedly well +founded, as some of the bacteria known to be the cause of garget are +gas-forming. + +=Bitter cheese.= In a previous chapter the bitter fermentation of milk +has been discussed. If milk containing large numbers of such +organisms is made into cheese, the bitterness is very likely to be +noted in it. Cheese made from milk containing few or no lactic +bacteria is likely to develop a bitter taste, due to the growth of +the digestive bacteria that are able to grow through the lack of +acid in the cheese. + +If the milk contains considerable numbers of yeasts, a sweet or +fruity flavor is apt to develop, due to the products of the +fermentation of the sugar by the yeast. This flavor resembles that +of fermented fruit, or the bouquet of certain kinds of wine. + +=Putrid cheese.= In the absence of acid-forming bacteria, the cheese +may develop a putrid or rotten odor, due to the growth of some types +of putrefactive or digesting bacteria. This trouble is very +infrequent in cheddar cheese, since this is made from ripened milk, +but occurs more frequently in those types in which no acid is +developed. + +Bacteria develop in the cheese in colonies or masses, just as they +do in the plate cultures of the bacteriologist, made with +transparent media, such as gelatin. Cheese is opaque; therefore, the +growing colonies cannot be readily discovered, but when +pigment-forming bacteria grow in the cheese, their presence is +likely to be noted, because of the colored spots that are formed. + +=Rusty spot.= The "rusty spot" that has been encountered in New York +and Canada is due to one of the colored bacteria which produces an +orange or yellowish-red pigment. Various other pigment-forming +organisms have been met in cheese, each producing its colored colony +which differentiates itself from the mass of the cheese. If the +pigment is produced in considerable quantities, and is soluble in +any of the constituents of the cheese, the color will not appear in +spots but will be more diffuse, or may impart a color to the entire +mass. + +Cases of acute poisoning arising from the ingestion of cheese are +not infrequently reported; similar instances result from the use of +ice cream. In both cases it is believed that poisonous products have +been formed by bacteria, probably by some of the putrefactive forms. + +From what has been said with reference to the abnormal fermentations +of cheese, it will be seen that they are always due to the lack of +acid-forming bacteria, or to their partial replacement by other +types. In order to prevent such troubles, it is necessary to insure +that the milk has been produced under clean conditions, from healthy +cows, and has been handled in such a manner as to reach the maker in +as sweet and fresh condition as possible. The maker can, by the use +of proper starters, control the kinds of bacteria essential for the +ripening process. A well trained maker should be able to prepare +from such milk a uniform product of the highest quality. The effort +of cheese makers at the present time is to handle milk of more or +less objectionable quality so as to secure from it as good cheese as +is possible. But cheese is so sensitive as to character of milk used +that greater effort should be spent in securing an improved supply. + +=Moldy cheese.= In the case of the cheddar cheese and other types of +hard cheese, it is essential that their surfaces be kept clean, and +not discolored by the growth of molds, which find favorable +conditions for growth on the surface of the cheese in the moist +atmosphere of the curing room. The molding of cheddar cheese can be +prevented by covering the cheese with a layer of paraffin which +stops the development of the mold spores, by shutting off the +necessary supply of oxygen. For this purpose the cheese are dipped +in melted paraffin when a few days old. + +In the case of types of cheese which are salted by applying the salt +to the surface, or with soft cheese which ripen from the outside, +other methods of mold prevention are employed, such as rubbing and +washing the cheese. The curing room itself may be freed from the +mold spores by the use of such standard disinfectants as formalin or +sulphur. + +=Swiss cheese.= One of the most important kinds of hard cheese, is the +Swiss or Emmenthaler, so named, from the country and valley in which +the cheese was first made. In America, this type was introduced by +Swiss immigrants, and is being made in constantly increasing +quantities in Ohio and Wisconsin. + +Swiss cheese is a hard firm type, appearing in the markets in the +form of the flat circular "drum" cheese, two to three feet in +diameter, and six to eight inches thick, or in the smaller "block" +form. In this country the cheese is prepared twice a day, since it +is necessary to work up the milk while it is perfectly sweet. +Indeed, the milk is received at the factories while it is still +warm, and within five or six hours after it is drawn from the cow +the cheese is on the press. If the attempt is made to prepare Swiss +cheese from the kind of milk that is best suited for cheddar +purposes, _i.e._, milk in which the acidity has increased to some +extent, the flavor of the resulting product is likely to approximate +a cheddar cheese rather than that of a Swiss. + +In the salting process, the salt is not mixed with the curd before +it is pressed, but is applied by immersing the cheese for a few days +in a saturated brine, and then rubbing salt over the surface of the +cheese. In this way the salt gradually diffuses quite uniformly +through the cheese. The method of salting has apparently a marked +influence on the ripening process, since if the salt is added in the +same way, and in amounts used in the cheddar process, the flavor +will not be that of a Swiss cheese but will resemble a cheddar. + +In cheddar cheese, the whey is expelled from the curd by means of +the acid which is developed in the curd, and by heating the curd to +a temperature of 95° F. to 100° F. In Swiss cheese the development +of acid during the making process is prevented, because of the +smaller number of acid-forming bacteria in the milk; other factors +must therefore contribute to the expulsion of the whey to secure a +firm curd. This is accomplished by cutting the curd into very small +pieces and by briskly stirring it during the making, heating it +during this process for a period of 20 to 30 minutes at 130° to 140° +F. It might be thought that this high temperature, which is +approximately that used in pasteurization would destroy the +acid-forming bacteria, but these are apparently protected as they +are within the curd. During the time the cheese is being pressed, +the contained bacteria begin to grow and the whey coming from the +cheese toward the end of the pressing shows a high acidity. If it +does not show such a development of acid, the maker has reason to +believe that the cheese may never ripen in a typical manner. + +It has been mentioned that the milk contains but few acid-forming +bacteria. The maker, however, attempts to insure the presence of a +sufficient number by the use of "home-made" rennet. This is prepared +by placing a piece of dried rennet, _i.e._, the stomach of the calf, +in whey, keeping the same in a warm place for twenty-four to +thirty-six hours. As the rennet contains acid-forming organisms, +these grow rapidly in the warm whey, so that by adding this sour +whey to the milk, the maker is not only adding rennet, that is to +curdle the milk, but also a small starter of lactic bacteria. If the +rennet thus prepared contains no harmful bacteria and the milk is of +good quality, the cheese is likely to ripen in a normal manner. The +rennet should be prepared with due regard to bacteriological +principles, a condition that is rarely met in Swiss factories in +this country. + +Swiss cheese has two striking characteristics, the flavor and the +presence of holes or "eyes." The flavor is sweetish rather than the +sharp and pungent flavor of cheddar cheese. The bacteria concerned +in its production are not known, but it is certain that specific +organisms play some role, since if the flora of the cheese is +changed by salting the curd or by the use of milk containing large +numbers of lactic bacteria, the flavor will also be changed. This +role of the acid-forming bacteria in Swiss is the same as in +cheddar, _i.e._, through the acid, conditions are established for +peptic action, the curd being partially digested while at the same +time the curd mass is protected from putrefactive processes. + +In Swiss cheese during the ripening process, holes about the size of +a large cherry develop which should be quite uniformly distributed +throughout the cheese. The inner surface of the hole is glistening +and, in a well-ripened cheese, a small quantity of clear brine, +_i.e._, "tears" may be noted. These holes or "eyes" may be called +the trade mark of the Swiss cheese, since without them the product +has a lessened commercial value, even if it possesses the typical +flavor. The "eyes" are caused by bacteria that ferment the lactic +acid produced by the lactic bacteria, forming from it propionic +acid and carbon dioxide, the latter gas being the cause of the hole +or "eye." + +[Illustration: Fig. 38.--Swiss Cheese. + +Normal development of "eyes" in a Swiss cheese. The eyes are +generally as large as a cherry.] + +The "eye"-forming organisms cannot grow in the presence of any +amount of salt, hence, if salt is added directly to the curd, the +cheese is likely to be "blind" or free from holes. The eyes are +formed not at the time gas holes are produced in a cheddar cheese, +_i.e._, early in the ripening process, but after a lapse of three or +four weeks. They are most abundant in the middle of the cheese since +the manner of salting is such as to inhibit their formation near the +surface. The eye-forming bacteria may have some effect on the flavor +of the cheese. + +The Swiss maker encounters the same troubles as does the cheddar +maker. Gassy cheese is more prevalent in the Swiss than in the +cheddar industry, since the maker cannot call to his aid the methods +used by the cheddar maker, viz., the addition of a heavy starter, +the washing of the curd, etc. It is especially important that the +quality of the milk be first class in every respect, and yet +customs prevail in the Swiss industry that are directly inimical to +the production of good milk. The grossest carelessness prevails at +the factories in the matter of handling the whey. It is often kept +in individual barrels for each patron. (See Fig. 8.) These are not +kept thoroughly clean and the result is that the whey taken back to +the farm in the cans that are used to bring the fresh milk is often +in an advanced stage of fermentation. + +There are many other kinds of hard cheese; but in each, so far as is +known, the role of the acid-forming bacteria is identical with that +noted in cheddar and Swiss cheese, viz, in preparing conditions +favorable for peptic action, and preventing the development of +putrefactive bacteria present in the curd. + +=Roquefort cheese.= Among the more important foreign types of cheese +that are characterized by the development of mold is Roquefort, so +named from the district in France in which it is made. This cheese +is made from sheep's milk, in much the same manner as cheddar. The +characteristic process in its preparation is the inoculation of the +curd, at the time it is put to press, with the spores of a +particular kind of mold, a type closely related to the ordinary +green mold of bread and cheese. The mold for inoculation is grown on +bread, the whole mass being dried so that it can be powdered; then +the ground-up material is sprinkled on the curd as it is placed in +the press hoops. The first stage in the ripening of Roquefort is +probably identical with that of the types of hard cheeses already +considered, the breaking-down of the curd being due to the pepsin of +the rennet used, which action is made possible by the acid formed by +the bacteria. + +The second stage in ripening, and one in which the characteristic +flavor of the cheese is developed, is due to the growth of the mold +with which the cheese is seeded. Molds can grow only in the presence +of air, and in order to provide this condition, the cheese are run +through a machine having a series of needle-like projections which +fills the cheese with fine holes. This allows the air to penetrate +the cheese and the mold to grow, the fruiting of which develops the +characteristic flavor. The changes produced by the mold are not well +understood, but the flavor is evidently connected with its +development since in the absence of mold, it does not appear. The +cheese must be cured under carefully controlled conditions, as to +temperature and moisture; in France these are secured by curing the +cheese in limestone caves that are highly saturated with moisture. +Attempts have been made to make Roquefort cheese in other parts of +the world, but they have never been successful, due undoubtedly to +the fact that the proper environment and conditions for the +development of the various types of organisms necessary in the +ripening process have not been met. This cheese is sold for 50 to 75 +cents per pound in the markets of the world. + +There are two other kinds of cheese that are closely related to +Roquefort, as to the manner of ripening, viz., the Gorgonzola of +Italy and the Stilton of England, both of which possess their +characteristic flavors by reason of the development of molds. In +Stilton cheese the mold is not intentionally added, the maker +relying on the contamination that comes from the factory for the +usual seeding. If this does not develop, it is sometimes inoculated +by exchanging plugs with a well-ripened Stilton. This method is not +so certain as in the inoculation of Roquefort. + +=Camembert cheese.= A typical example of soft cheese is one of the +French types, known as Camembert. This cheese is prepared from cow's +milk which is curdled by rennet. The curd is not cut but is dipped +into the forms, which condition, taken with the absence of pressure +in forming the cheese, accounts for the large quantity of whey in +it. The finished cheese are about one inch in thickness and three +inches in diameter. In the ripening, the moisture and temperature of +the curing room are very carefully regulated. + +The first stage in the ripening is due to the rennet and the lactic +bacteria. Later there appears on the surface of the moist cheese, a +moldy growth. In this, there are at least two kinds of molds, the +ordinary mold that appears on sour milk, _Oidium lactis_, and +another that is related to the bread mold but which has a white +instead of a green fruiting stage. These molds are confined to the +surface of the cheese but the enzymes which they produce diffuse +into the substance, changing the color from a dull, opaque white to +a translucent yellow. The acid that has been formed by the lactic +bacteria is gradually used up by the growth of the mold, and +conditions then become favorable for the growth of putrefactive +bacteria which digest the curd. The cheese is ready for use when the +action of the mold has penetrated to the center of the cheese, and +before any pronounced putrefaction has taken place. The production +of the typical flavor is dependent upon there being a definite +relation between the growth of the molds and bacteria. This relation +is dependent largely upon the moisture and temperature of the curing +room. These cannot always be regulated with exactness; and hence, +much of this type of cheese is not of first quality, and must be +sold for a low price. While such fancy cheeses, as Camembert, bring +fifty cents and upward per pound, and the yield from the milk is +much greater than with the hard type of cheese, yet the difficulties +of successful manufacture are such as to make success less easily +attained than with the other types. + +There are many other kinds of soft cheese that depend for their +ripening upon factors similar to those concerned in the ripening of +Camembert; most of them are, however, of small importance from a +commercial standpoint. + +=Limburger cheese.= A very famous cheese is one originally made in +Germany to which the name Limburger is given. It is classed as a +soft cheese although it is much firmer than Camembert. This cheese +is made from cow's milk and is pressed very lightly or not at all, +which condition accounts for its high per cent (50 per cent) of +moisture. The surface is kept moist by repeated washing of the +cheese, and by keeping the air of the curing room very moist. A +yellowish, slimy, bacterial layer soon develops on the surface under +these conditions. The enzymes produced by this external growth +gradually diffuse to the center of the cheese, when it is regarded +as ripe. The odor of the matured product is somewhat putrefactive, +but is not so offensive as is usually supposed. + +Definite knowledge concerning the types of organisms concerned in +the surface layer is very limited. It is not certain whether the +same kinds of organisms must always be present. Limburger is much +easier to make than Camembert, due possibly to the fact that there +are not needed definite forms of life and that the balance between +them is not so delicate. + +A cheese known as brick is closely related to Limburger in its +method of making and of ripening but is less pronounced in flavor. + +In the manufacture of all of these types of cheese, troubles are +likely to develop, due to an abnormal bacterial condition of the +milk. + +It will be seen from what has been said that the bacteria are +essential factors in cheese ripening, and that the cheese industry, +like the butter industry, may be called a true fermentation +industry. Close co-operation must exist between the milk producer, +and the maker so that the type of fermentation that goes on in the +milk can be controlled. A recognition of the fundamental principles +governing these fermentations, both normal as well as abnormal, is +now regarded as an essential part of the training of the dairy +manufacturer of today. + + + + +CHAPTER IX. + +BACTERIA IN MARKET MILK. + + +Within the last decade attention has been especially directed toward +the quality of milk that is furnished to the people in the cities. +This has come about, in part, in connection with the demands made +for better and purer food of every kind. These demands are reflected +in the pure-food laws enacted by the federal government, and by the +various states and municipalities. Another factor that has focused +attention on the milk supplies has been the belief that it plays an +important role in the production and distribution of disease, +especially among children. The rapid growth of cities in all of the +great countries of the world, the higher standard of living, and the +greater demand for milk and other dairy products, has, of necessity, +widened the zone from which the milk supply of any particular city +must be drawn. Milk is now an article of export and of import; some +of the great cities draw a portion of their supply from farms +hundreds of miles away. This means that a longer time must elapse +between the time of production and consumption, necessitating the +exercise of greater care in production and handling in order to +preserve the milk until it reaches the consumer. + +In the past in the cities, as in the smaller towns at present, the +supply was largely furnished by the producer directly to the +consumer. This direct contact afforded the consumer the opportunity +of informing himself of the conditions under which his milk supply +was produced if he desired. The advent of the middleman in the +business, and the gathering of the milk from many hundreds of farms, +and its redistribution to thousands of homes has made it impossible +for the individual consumer to learn anything of the conditions +surrounding production. When the individual cannot protect himself +against fraud and unhealthful conditions, it is the duty of the +government to protect him. This is the theory underlying the modern +control of food supplies, water supplies, and of living conditions +in general. Acting on this basis the cities are seeking to control, +to an increasing degree, the healthfulness and cleanliness of the +milk supply. + +Formerly such control as was given was largely with reference to the +composition of the milk, the regulations providing that it should +contain not less than a minimum amount of fat and other solids, and +be free from preservatives. The more modern regulations are much +more complex and touch every phase of production and handling that +can, in any way, affect the value of the milk as human food. + +=Municipal regulations.= The different cities vary widely in the +methods employed to secure a satisfactory milk supply. Rules and +regulations are adopted to which the producer and dealer must +conform. In order to ascertain whether the regulations are being +obeyed, two types of examinations may be made: first the inspection +of the farms and of the plants of the dealers; second the +examination of the milk itself with reference to its chemical +composition, bacterial content and temperature. + +The city of New York is doing more to safeguard and to improve its +milk supply than any other large city in this country. A brief +summary of its regulations and methods follow. A copy of the rules +is furnished to each dairyman and is supposed to be posted in the +stable. + + +The Cows. + +1. The cows must be kept clean, and manure must not be permitted to +collect upon the tail, sides, udder and belly of any milch cow. + +2. The cows should be groomed daily, and all collections of manure, +mud or other filth must not be allowed to remain upon their flanks, +udders or bellies during milking. + +3. The clipping of long hairs from the udder and flanks of the cows +is of assistance in preventing the collection of filth which may +drop into the milk. The hair on the tails should be cut, so that the +brush will be well above the ground. + +4. The udders and teats of the cow should be thoroughly cleaned +before milking; this to be done by thorough brushing and the use of +a cloth and warm water. + +5. To prevent the cows from lying down and getting dirty between +cleaning and milking, a throat latch of rope or chain should be +fastened across the stanchions under the cow's neck. + +6. Only feed which is of good quality and only grain and coarse +fodders which are free from dirt and mould should be used. +Distillery waste or any substance in a state of fermentation or +putrefaction must not be fed. + +7. Cows which are not in good flesh and condition should be +immediately removed and their milk kept separate until their health +has been passed upon by a veterinarian. + +8. An examination by a veterinary surgeon should be made at least +once a year. + + +The Stable. + +9. No stagnant water, hog-pen, privy or uncovered cesspool or manure +pit should be maintained within 100 feet of the cow stable. + +10. The cow stable should be provided with some adequate means of +ventilation, either by the construction of sufficient air chutes +extending from the room in which the cows are kept to the outside +air, or by the installation of muslin stretched over the window +openings. + +11. Windows should be installed in the cow barn to provide +sufficient light (2 sq. feet of window light to each 600 cubic feet +of air space the minimum) and the window panes be washed and kept +clean. + +12. There should be at least 600 cubic feet of air space for each +cow. + +13. Milch Cows should be kept in a place which is used for no other +purpose. + +14. Stable floors should be made water-tight, be properly graded and +well drained, and be of some non-absorbent material. Cement or brick +floors are the best, as they can be more easily kept clean than +those of wood or earth. + +15. The feeding troughs and platforms should be well lighted and +kept clean at all times. + +16. The ceiling should be thoroughly swept down and kept free from +hanging straw, dirt and cobwebs. + +17. The ceiling must be so constructed that dust and dirt therefrom +shall not readily fall to the floor or into the milk. If the space +over the cows is used for storage of hay, the ceiling should be made +tight to prevent chaff and dust from falling through. + +18. The walls and ledges should be thoroughly swept down and kept +free from dust, dirt, manure or cobwebs, and the floors and +premises be kept free from dirt, rubbish and decaying animal or +vegetable matter at all times. + +19. The cow beds should be so graded and kept that they will be +clean and sanitary at all times. + +20. Stables should be whitewashed at least twice a year unless the +walls are painted or are of smooth cement. + +21. Manure must be removed from the stalls and gutters at least +twice daily. This must not be done during milking, nor within one +hour prior thereto. + +22. Manure should be taken from the barn, preferably drawn to the +field. When the weather is such that this cannot be done, it should +be stored not nearer than 200 ft. from the stable and the manure +pile should be so located that the cows cannot get at it. + +23. The liquid matter should be absorbed and removed daily and at no +time be allowed to overflow or saturate the ground under or around +the cow barn. + +24. Manure gutters should be from six to eight inches deep, and +constructed of concrete, stone or some non-absorbent material. + +25. The use of land plaster or lime is recommended upon the floors +and gutters. + +26. Only bedding which is clean, dry and absorbent should be used, +preferably sawdust, shavings, dried leaves or straw. No horse manure +should be used as bedding. + +27. The flooring where the cows stand should be so constructed that +all manure may drop into the gutter and not upon the floor itself. + +28. The floor should be swept daily. This must not be done within +one hour prior to milking time. + +29. If individual drinking basins are used for the cows, they should +be frequently drained and cleaned. + +30. All live stock other than cows should be excluded from the room +in which the milch cows are kept. (Calf or bull pens may be allowed +in the same room if kept in the same clean and sanitary manner as +the cow beds.) + +31. The barnyard should be well drained and dry, and should be as +much sheltered as possible from the wind and cold. Manure should not +be allowed to collect therein. + +32. A suitable place in some separate building should be provided +for the use of the cows when sick, and separate quarters must be +provided for the cows when calving. + +33. There should be no direct opening from any silo or grain pit +into the room in which the milch cows are kept. + + +The Milk House. + +34. A milk house must be provided which is separated from the stable +and dwelling. It should be located on elevated ground, with no +hog-pen, privy or manure pile within 100 feet. + +35. It must be kept clean and not used for any purpose except the +handling of milk. + +36. The milk house should be provided with sufficient light and +ventilation, with floors properly graded and made water-tight. + +37. It should be provided with adjustable sashes to furnish +sufficient light and some proper method of ventilation should be +installed. + +38. The milk house should be provided with an ample supply of clean +water for cooling the milk, and if it is not a running supply, the +water should be changed twice daily. Also a supply of clean ice +should be provided to be used for cooling the milk to 50 degrees +within two hours after milking. + +39. Suitable means should be provided within the milk house, to +expose the milk pails, cans and utensils to the sun or to live +steam. + +40. Facilities consisting of wash basins, soap and towel should be +provided for the use of milkers before and during milking. During +the Summer Months the Milk House should be properly screened to +exclude flies. + + +The Milkers and Milking. + +41. Any person having any communicable or infectious disease, or one +caring for persons having such disease, must not be allowed to +handle the milk or milk utensils. + +42. The hands of the milkers must be thoroughly washed with soap and +water, and carefully dried on a clean towel before milking. + +43. Clean overalls and jumpers should be worn during the milking of +the cows. They should be used for no other purpose, and when not in +use should be kept in a clean place protected from dust. + +44. The hands and teats should be kept dry during milking. The +practice of moistening the hands with milk is to be condemned. + +45. The milking stools should be at all times kept clean, and iron +stools are recommended. + +46. The first streams from each teat should be rejected, as this +fore milk contains more bacteria than the rest of the milk. + +47. All milk drawn from the cows 15 days before, or 5 days after +parturition should be rejected. + +48. The pails in which the milk is drawn should have as small an +opening at the top as can be used in milking; top opening preferably +not to exceed 8 inches in diameter. This lessens the contamination +by dust and dirt during milking. + +49. The milking should be done rapidly and quietly, and the cows +should be treated kindly. + +50. Dry fodder should not be fed to the cows during or just before +milking, as dust therefrom may fall into the milk. + +51. All milk utensils, including pails, cans, strainers, and +dippers, must be kept thoroughly clean and must be washed and +scalded after each using, and all seams in these utensils should be +cleaned, scraped and soldered flush. + + +The Milk. + +52. Milk from diseased cows must not be shipped. + +53. The milk must not be in any way adulterated. + +54. The milk as soon as drawn should be removed to the milk house +and immediately strained and cooled to the proper temperature. + +55. All milk must be cooled to a temperature below 50 degrees F., +within two hours after being drawn, and kept thereafter below that +until delivered to the creamery. + +56. The milk should be strained into cans which are standing in ice +water which reaches the neck of the can. The more rapidly the milk +is cooled, the safer it is, and longer it will keep sweet. Ice +should be used in cooling milk, as very few springs are cold enough +for the purpose. + +57. If aerators are used, they should stand where the air is free +from dust or odors, and on no account should they be used in the +stable or out of doors. + +58. Milk strainers should be kept clean; scalded a second time just +before using, and if cloth strainers are used, several of them +should be provided, in order that they may be frequently changed +during the straining of the milk. + +59. The use of any preservative or coloring matter is adulteration, +and its use by a producer or shipper will be a sufficient cause for +the exclusion of his product from the City of New York. + + +Water Supply. + +60. The water supply used in the dairy and for washing utensils +should be absolutely free from any contamination, sufficiently +abundant for all purposes, and easy to access. + +61. This supply should be protected against flood or surface +drainage. + +62. The privy should be located not nearer than 100 feet of the +source of the water supply, or else be provided with a water-tight +box that can be readily removed and cleaned, and so constructed that +at no time will the contents overflow or saturate the surrounding +ground. + +63. The source of the water supply should be rendered safe against +contamination by having no stable, barnyard, pile of manure or other +source of contamination located within 200 feet of it. + +In order that the farm inspection shall be as effective as possible, +and to make the work of the several inspectors as uniform as may be, +the dairies are scored. A copy of the score card follows. + + + DEPARTMENT OF HEALTH + + The City of New York + + =Division of General= + =Sanitary Inspection= =Dairy Report= + + Inspection No. ... Time...... A. P. M. Date......191.. + + 1 =Dairyman=.................. =Owner= ..................... + 2 =P. O. Address=............. =P.O. Address=.......State... + 3 =County=..... State..... =Party Interviewed=............ + 4 Milk delivered to Creamery at.......... Formerly at......... + 5 Operated by.................. Address....................... + 6 Distance of farm from Creamery..... Occupied farm since..... + 7 No. Cows....... No. Milking...... No. Qts. Produced......... + 8 All persons in the households of those engaged in producing + or handling milk are............free from all infectious + disease. Weekly reports are..................being filed + .......................................................... + 9 Date and nature of last case on farm........................ + 10 =WATER SUPPLY= for utensils is from a............... located + .......... feet deep and apparently is............ pure and + wholesome............ State any possible contamination + located within 200 feet of source of water supply or + if water supply is not protected against surface drainage + ........................................................... + ........................................................... + 11 Water supply on this farm analyzed.... 191.. Result........ + 12 Style of Cow Barn.... Length.... ft. Width.... ft. Height + of ceiling.... ft. + 13 =Dairy Rules= of the Department of Health are........ posted + .................. + 14 =Dairy Herd= examined by............. on.............. 191.. + Report............ + + ================================================================= + |Perfect| Allow | + ----------------------------------------------------------------- + EQUIPMENT | | | + | | | + 15 =COW STABLE= is.......located on elevated | | | + ground with no stagnant water, hog-pen, | | | + privy, uncovered cesspool or manure pit | | | + within 100 feet | 1 | ..... | + | | | + 16 =FLOORS=, other than cow beds, are | | | + of concrete or some non-absorbent material | 2 | ..... | + | | | + 17 Floors are...properly graded and water-tight | 2 | ..... | + | | | + 18 =Cow beds are=...of concrete or planks | | | + laid on concrete | 2 | ..... | + | | | + 19 =DROPS= are.....constructed of concrete, | | | + stone or some non-absorbent material | 2 | ..... | + | | | + 20 Drops are......water-tight and space beneath | | | + is clean and dry. | 2 | ..... | + | | | + 21 =CEILING= is constructed of.......and is | | | + tight and dust proof | 2 | ..... | + | | | + 22 =WINDOWS= No.......total square feet | | | + there is...........2 square feet of window | | | + light for each 600 cu. ft. air space (1 | | | + sq. ft. per each 600 cu. ft.--1) | 2 | ..... | + | | | + 23 =VENTILATION= consists of ......sq. ft. muslin| | | + in ceiling or..........which is sufficient | | | + 3, fair 2, poor 1, insufficient 0 | 3 | ..... | + | | | + 24 =AIR SPACE= is......cu. ft. per cow (600 and | | | + over--3) (500 to 600--2) (400 to 500--1) | | | + (under 400--0) | 3 | ..... | + | | | + 25 =LIVE STOCK=, other than cows, are....excluded| | | + from rooms in which milch cows | | | + are kept | 2 | ..... | + | | | + 26 There is..........direct opening from stable | | | + into silo or grain pit | 1 | ..... | + | | | + 27 Separate quarters are...........provided for | | | + cows when calving or sick | 1 | ..... | + | | | + 28 =COW YARD= is..............properly graded and| | | + drained | 2 | ..... | + | | | + 29 =WATER SUPPLY= for cows is..........unpolluted| | | + and plentiful | 1 | ..... | + | | | + 30 =MILK HOUSE= has...........direct opening into| | | + cow barn or other building | 1 | ..... | + | | | + 31 Milk house has..........sufficient light and | | | + ventilation | 1 | ..... | + | | | + 32 Floor is.................properly graded and | | | + water-tight | 1 | ..... | + | | | + 33 Milk house is...........properly screened to | | | + exclude flies | 1 | ..... | + | | | + 34 Milk pails are............of smoothly tinned | | | + metal in good repair | 1 | ..... | + | | | + 35 =MILK PAILS= have...........all seams soldered| | | + flush | 2 | ..... | + | | | + 36 Milk pails are..........of the small mouthed | | | + design, top opening not exceeding 8 inches | | | + in diameter. Diameter | 2 | ..... | + | | | + 37 =Racks are=........provided to hold milk pails| | | + and cans when not in use | 2 | ..... | + | | | + 38 =Special milking suits= are......provided | 1 | ..... | + |-------|-------| + | 40 | | + | | | + =METHODS= | | | + | | | + 39 =STABLE INTERIOR= painted or whitewashed | | | + on.......which is satisfactory 3, fair 2, | | | + unsatisfactory 1, never 0 | 3 | ..... | + | | | + 40 =FEEDING TROUGHS=, platforms or cribs are | | | + ......well lighted and clean | 1 | ..... | + | | | + 41 =Celling= is..........free from hanging straw,| | | + dirt or cobwebs | 3 | ..... | + | | | + 42 =Window panes= are.............washed and kept| | | + clean | 1 | ..... | + | | | + 43 =WALLS AND LEDGES= are...............free from| | | + dirt, dust, manure or cobwebs | 2 | ..... | + | | | + 44 =FLOORS AND PREMISES= are.......free from | | | + from dirt, rubbish or decayed animal or | | | + vegetable matter | 2 | ..... | + | | | + 45 =COW BEDS= are.........clean, dry and no horse| | | + manure used thereon | 2 | ..... | + | | | + 46 =Manure= is.......removed to field daily 4, | | | + to at least 100 feet from barn 2, stored | | | + less than 100 feet or where cows can get | | | + at it 0 | 4 | ..... | + | | | + 47 =Liquid Matter= is....... allowed to saturate | | | + ground under or around cow barn | 2 | ..... | + | | | + 48 =Milking stools= are.......clean | 1 | ..... | + | | | + 49 =Cow Yard= is.......clean and free from | | | + manure | 2 | ..... | + | | | + 50 =COWS= have......been tuberculin tested and | | | + all tuberculous cows removed | 7 | ..... | + | | | + 51 Cows are.....all in good flesh and condition | | | + at time of inspection | 2 | ..... | + | | | + 52 Cows are.....all free from clinging | | | + manure and dirt. (No. dirty.....) | 4 | ..... | + | | | + 53 =LONG HAIRS= are.....kept short on belly, | | | + flanks, udder and tail | 1 | ..... | + | | | + 54 =UDDER AND TEATS= of cows are...... | | | + thoroughly brushed and wiped with a | | | + clean damp cloth before milking | 3 | ..... | + | | | + 55 =ALL FEED= is.....of good quality and | | | + distillery waste or any substance in a state | | | + of putrefaction is......fed | 2 | ..... | + | | | + 56 =MILKING= is.....done with dry hands | 2 | ..... | + | | | + 57 =FORE MILK= or first few streams from each | | | + teat is.....discarded | 2 | ..... | + | | | + 58 =Clothing= of milkers is.....clean | 1 | ..... | + | | | + 59 Facilities for washing hands of milkers are | | | + ......provided in cow barn or milk | | | + house | 2 | ..... | + | | | + 60 =Milk= is strained at.....and.....in | | | + clean atmosphere | 1 | ..... | + | | | + 61 Milk is.....cooled within two hours after | | | + milking to 50 degrees F. 3, to 55 degrees | | | + F. 2 to 60 degrees F. 1 | 3 | ..... | + | | | + 62 Ice is.....used for cooling milk | 1 | ..... | + | | | + 63 =MILK HOUSE= is.....free from dirt, rubbish | | | + and all material not used in the | | | + handling and storage of milk | 1 | ..... | + | | | + 64 =Milk utensils= are.....rinsed with cold | | | + water immediately after using and washed | | | + clean with hot water and washing solution | 2 | ..... | + | | | + 65 Utensils are.....sterilized by steam or | | | + boiling water after each using | 2 | ..... | + | | | + 66 =Privy= is.....in sanitary condition, with | | | + vault and seats.....covered and protected | 1 | ..... | + | | | + |-------|-------| + | 60 | | + +Remarks + + Equipment 40 per cent. Score .... per cent + Methods 60 per cent. Score .... per cent + Perfect Dairy 100 per cent. Score .... per cent + + +A copy of the completed report is left with the dairyman. + +Before the farm inspection is carried out the creameries to which +the milk is delivered by the farmers are inspected at the time the +milk is being delivered. The temperature of the milk and its +cleanliness are noted. In the creamery the straining, cooling and +handling of the milk are observed as well as the washing of the milk +cans and other utensils, and the construction and condition of the +creamery, the opportunity for the water supply to become +contaminated, and the presence of infectious diseases among the +employees. + +=Grades of milk.= Three grades of milk have been established. Each +dealer is required to state which grade or grades he expects to +handle. The specifications for the different grades are as follows. + +_Grade A. Guaranteed Milk._ Guaranteed milk is that produced at +farms holding permits therefor from the Department of Health and +produced and handled in accordance with the following minimum +requirements, rules and regulations: + +1. Only such cows shall be admitted to the herd as have not re-acted +to a diagnostic injection of tuberculin. + +2. All cows shall be annually tested with tuberculin, and all +re-acting animals shall be excluded from the herd. + +3. No milk from re-acting animals shall be shipped to the City of +New York for any purpose whatever. + +4. The milk shall not contain more than 30,000 bacteria per c. c. +when delivered to the consumer, or at any time prior to such +delivery. + +5. The milk shall be delivered to the consumer only in sealed +bottles, which have been sealed at the dairy. + +6. The milk shall be delivered to the consumer within 30 hours of +the time at which it was drawn. + +_Grade A. Certified Milk._ Certified milk is milk certified by a +milk commission appointed by the Medical Society of the County of +New York, or the Medical Society of the County of Kings, as being +produced under the supervision and in conformity with the +requirements of that commission as laid down for certified milk, and +sold under a permit therefor issued by the Board of Health. + +No milk shall be held, kept, offered for sale, or sold and delivered +as certified milk in the City of New York which is produced under +requirements less than those for guaranteed milk. + +_Grade A. Inspected Milk--Raw._ Inspected milk (raw) is milk +produced at farms holding permits therefor from the Board of Health, +and produced and handled in accordance with the following minimum +requirements, rules and regulations: + +1. Only such cows shall be admitted to the herd as have not re-acted +to a diagnostic injection of tuberculin. + +2. All cows shall be tested annually with tuberculin, and all +re-acting animals shall be excluded from the herd. + +3. No milk from re-acting animals shall be shipped to the City of +New York for any purpose whatsoever. + +4. The farms at which the milk is produced must obtain at least 75 +points in an official score of the Department of Health. These 75 +points shall be made up as follows: A minimum of 25 points for +equipment, and 50 points for method. + +5. The milk shall not contain more than an average of 60,000 +bacteria per c. c. when delivered to the consumer, or at any time +prior thereto. + +6. Unless otherwise specified in the permit, the milk shall be +delivered to the consumer only in bottles. + +_Grade A. Selected Milk--Pasteurized._ Selected milk (pasteurized) +is milk produced at farms holding permits therefor from the Board of +Health, and produced and handled in accordance with the following +requirements, rules and regulations: + +1. The farms at which the milk is produced must obtain at least 60 +points in an official score of the Department of Health. Of these 60 +points, a minimum of 20 points shall be required for equipment and a +minimum of 40 points for method. + +2. All milk of this grade shall be pasteurized, and said +pasteurization shall be carried on under a special permit issued +therefor by the Board of Health, in addition to the permit for +"Selected Milk (Pasteurized.)" + +3. The milk shall not contain more than an average of 50,000 +bacteria per c. c. when delivered to the consumer, or at any time +after pasteurization and prior to such delivery. + +4. Unless otherwise specified in the permit, the milk shall be +delivered to the consumer only in bottles. + +5. All containers in which pasteurized milk is delivered to the +consumer shall be plainly labeled "Pasteurized." Labels must also +bear the date and hour when pasteurization was completed, the place +where pasteurization was performed, and the name of the person, firm +or corporation performing the pasteurization. + +6. The milk must be delivered to the consumers within 30 hours after +the completion of the process of pasteurization. + +7. No milk shall be pasteurized more than once. + +8. No milk containing in excess of 200,000 bacteria per c. c. shall +be pasteurized. + +_General Regulations for Grade A_-- + +1. The caps of all bottles containing milk of Grade A shall be +white, and shall contain the words "Grade A" in black letters, in +large type. + +2. If cans are used for the delivery of milk for Grade A, the said +cans shall have affixed to them white tags, with the words "Grade A" +printed thereon in black letters, in large type, together with the +designation "Inspected Milk (Raw)" or "Selected Milk (Pasteurized)," +as the quality of the contents may require. + +_Grade B. Selected Milk--Raw._ Selected milk (raw) is milk produced +at farms holding permits therefor from the Board of Health, and +produced and handled in accordance with the following minimum +requirements, rules and regulations: + +1. Only such cows shall be admitted to the herd as have been +physically examined by a regularly qualified veterinarian and +declared by him to be healthy, and free from tuberculosis in so far +as a physical examination may determine that fact. + +2. The farms at which the milk is produced must obtain at least 68 +points in an official score of the Department of Health. These 68 +points shall be made up as follows: A minimum of 25 points for +equipment, and a minimum of 43 points for method. + +3. The milk shall not contain an excessive number of bacteria when +delivered to the consumer, or at any time prior thereto. + +_Grade B. Pasteurized Milk._ Pasteurized milk (Grade B) is milk +produced under a permit issued therefor by the Board of Health, +and produced and handled in accordance with the following minimum +requirements, rules and regulations and in further accordance with +the special rules and regulations relating to the pasteurization of +milk. + +1. The milk after pasteurization must be at once cooled and placed +in sterilized containers, and the containers immediately closed. + +2. All containers in which pasteurized milk is delivered to the +consumer shall be plainly labeled "Pasteurized". Labels must also +bear the date and hour when the pasteurization was completed, the +place where pasteurization was performed, and the name of the +person, firm or corporation performing the pasteurization. + +3. The milk must be delivered to the consumer within 36 hours after +the completion of the process of pasteurization. + +4. No milk shall be pasteurized more than once. + +5. No milk containing an excessive number of bacteria shall be +pasteurized. + +_General Regulations for Grade B_-- + +1. Caps of bottles containing milk of grade B shall be white and +marked "Grade B" in bright green letters of large type. + +2. The necks and shoulders of cans containing grade B milk shall be +painted bright green, and a metal tag shall be attached to each can +with the words "Grade B" in large type, and the words of the +subdivision to which the quality of the milk in said can conforms. + +_Grade C._ Grade C is to be used for cooking and manufacturing +purposes only. It includes all raw milk that does not conform to the +requirements of any of the subdivisions of grade A or grade B. + +1. The caps of all bottles containing milk of grade C shall be white +and shall contain in red the words "Grade C" in large type and "for +cooking" in plainly visible type. + +2. Cans containing milk of grade C shall be painted red on necks and +shoulders and shall have in red the words "Grade C" in large type +and the words "for cooking" in plainly visible type affixed to each +can. + +All creameries handling milk of different grades will be required to +demonstrate to the Department of Health that they are capable of +keeping the grades separate, and must keep records satisfactory to +the Department of Health concerning the amount of milk of each grade +handled each day. + +It is to be noted that the grades of milk are based on the bacterial +content of the milk and on the opportunity for the milk to become +contaminated with pathogenic organisms. From the statements made in +a previous chapter it is evident that the number of bacteria in any +sample of milk is dependent upon (1) the original amount of +contamination, (2) the age of the milk, and (3) the temperature at +which it has been held. A high bacterial content is indicative of +poor milk, while a low bacterial content can be obtained, in the +case of raw milk, only where due attention is paid to cleanliness +and cooling. This relation between the quality of milk and its +bacterial content has led many cities to adopt numerical bacterial +standards, even when grades of milk have not been established. +Boston requires that the milk shall not contain more than 500,000 +bacteria per cubic centimeter. Rochester, N. Y., has a standard of +100,000 per cubic centimeter, while Chicago requires that the milk +on arrival in the city shall not contain more than 1,000,000 per +cubic centimeter from May first to September thirtieth, and not over +500,000 between October first and April thirtieth. The sale of milk +containing more than 3,000,000 bacteria per cubic centimeter is +prohibited. + +It has been urged that bacterial standards are not of value since +the healthfulness of milk depends on the kind of bacteria present +rather than on the number. It is well recognized that milk +containing millions of acid-forming organisms, butter milk, is a +healthful food, while that containing many less bacteria may contain +some disease-producing organisms. It has been urged that a +qualitative standard should supplant the quantitative. The consumer +desires milk that has been produced under clean conditions, and +which has good keeping qualities. The harmless forms of bacteria +exert the greatest influence on the keeping quality. Experience has +shown that the quantitative examination of the milk supply as +it comes from the farm is the most feasible method of determining, +in the laboratory, whether the farmer has obeyed the rules +with reference to cleanliness and cooling of the milk. The +bacteriological examination also gives an indication as to whether +the large number of bacteria is due to gross contamination of the +milk with mud and manure, or actual growth of bacteria as in old +milk. In the latter case the ordinary acid-forming bacteria will +usually predominate in the milk, while in the former, the number of +kinds of bacteria and the proportion between the kinds will be +changed. It is of course evident that the quantitative standards +should be applied with judgment. + +It is also claimed that the delay in securing the results in the +quantitative examination of milk is an objection to the bacterial +standard, since the milk is consumed before the laboratory findings +can be obtained. It is true that it does not protect the community +as far as the particular sample is concerned, but it is also true +that the examination is not made for the purpose of determining the +condition of the particular sample, so much as it is to determine +the methods that are employed on any particular farm, and these do +not vary widely from day to day. Thus, if a number of samples give +high results, it is evident that conditions surrounding production +need investigation. + +If the milk is well cooled on the farm, and kept cold while being +shipped, the growth of bacteria will be slow, and the condition of +the milk as far as keeping quality is concerned, much better than if +less care is used. Some cities have temperature standards; New York +requires that the milk shall be cooled to 50° F. on the farm, and +shall not be above 50° F. on arrival in the city. Others require +that it shall not be above 50° F. on delivery to the consumer. + +=Certified milk.= In many cities the Medical Societies have appointed +Milk Commissions, that adopt rules and regulations, concerning the +production of milk that shall receive the certificate of the +commission. Producers, who desire to have their milk thus certified, +must satisfy the commission that they are able to conform to the +rules. The commission appoints a physician to examine the personnel +of the farm, a veterinarian to make frequent examinations of the +herd, a chemist to examine the milk as to its contents in fat and +other solids, and a bacteriologist to determine the bacterial +content of the milk. The rules are very stringent and cover every +point that may influence, in any way, the value of the milk as human +food. In order to conform to these requirements, a heavy +expenditure must be incurred, and the business must pay for such +expert service; hence, certified milk must be sold at high prices, +twelve to twenty-five cents per quart. This price makes it a special +product and its use is confined mainly to infant feeding. + +The bacterial standard for certified milk is usually 10,000 bacteria +per cubic centimeter. It is only by the exercise of the greatest +care at every point that the bacterial content can be kept below +this maximum. + +The term "certified milk" has been registered by Mr. Francisco of +New Jersey, who was the first to engage in the production of such +milk under the direction of the Medical Milk Commission of Essex +County, New Jersey. The use of the term is allowed when the milk is +produced under the regulation of any Medical Milk Commission. + +Most certified milk is now produced on fancy dairy farms conducted +by wealthy men. The barns and other equipment are the best that can +be obtained, and the methods employed, as far as cleanliness is +concerned, are extreme. In some of the dairies the bacterial content +is reduced to a few hundred per cubic centimeter, or to that which +is derived from the interior of the udder. Such milk will, when well +refrigerated, keep for long periods of time. It is a not uncommon +thing for such milk to keep perfectly sweet for ten to fifteen days. + +=Tests for the quality of milk.= At the milk depot and elsewhere, it +is frequently desired to determine the bacterial condition of the +milk in a less refined manner than by the plate cultures of the +bacteriologist, which require a large amount of time for their +preparation and do not yield any positive information for at least +twenty-four hours. There are a number of such tests that may be +applied. + +[Illustration: Fig. 39.--Sediment Testers. + +In the use of the apparatus on the right, increased air pressure is +used to hasten the filtering process; the same is accomplished in +the apparatus shown in the center by warming the milk by the +injection of steam between the walls of the double jacket.] + +1. _Dirt or sediment test._ This is made by filtering a pint of the +mixed milk through a small disc of absorbent cotton. The insoluble +dirt is retained and imparts a color to the cotton, the shade of +which is dependent on the amount of dirt (P. 45). Since it is +impossible to have dirt without bacteria, it is evident that milks +containing a large amount of dirt will be high in bacteria. The +reverse, however, is not necessarily true. + +[Illustration: Fig. 40.--Good Milk. + +A plate culture inoculated with 1/100 of a cubic centimeter of milk +containing 67 colonies, which equals 6,700 bacteria per cubic +centimeter of milk. Such milk will keep well.] + +2. _Acidity test._ The acidity of the milk is also an indication of +its bacterial content. If the acidity has increased, above the +normal for fresh milk, the bacterial content is certain to be high, +and the keeping quality poor. An acidity above 0.2 per cent in +market milk is to be avoided, as an increase in acidity is always +preceded by a great increase of bacteria. + +Whether the acidity is above or below this point can be rapidly and +easily determined at the receiving station by a modification of +the Farrington acid test. Dissolve one alkaline tablet in an ounce +of water. A unit volume of this solution added to a unit volume of +milk is equal to 0.1 per cent of acidity. If two measures are +provided,--one for the alkaline solution holding just twice as much +as that used for the milk, the approximate acidity can be quickly +determined by mixing a measure of each in a common white cup. If the +acidity is above 0.2 per cent the color will remain white; if a pink +color develops, it indicates an acidity less than this amount. +This test is also useful in the selection of milk or cream that is +to be used for special purposes, such as pasteurization. + +[Illustration: Fig. 41.--Poor Milk. + +A plate culture inoculated with 1/1000 of a cubic centimeter of +market milk containing 1,680 colonies, which equals 1,680,000 +bacteria per cubic centimeter. Such milk has poor keeping +qualities.] + +3. _Alcohol test._ A test giving similar information is made by +adding two parts of 70 per cent alcohol to one part of milk, and +noting whether curdling occurs. + +4. _Curd test._ The curd test described on p. 100 gives no +indication of the number of bacteria present, only concerning the +types present. It has been proposed to combine the fermentation test +with the reduction test referred to below and thus gain some idea +of, not only the number, but the kinds of bacteria present. + +5. _Reduction test._ The reduction test is made by adding to twenty +cubic centimeters of milk, one-half cubic centimeter of a solution +of methylene blue, a coal tar dye. A saturated solution of the dye +is made in alcohol, and 2.5 per cent of this solution added to +water. The time required for the reduction of the dye or the change +of the color from blue to white when the samples are placed in tubes +and kept at 98 to 100° F., is dependent upon the number of bacteria +present. By allowing the tubes to stand until curdling occurs, and +noting the nature of the curd, whether the solid curd of the +desirable acid-forming bacteria or the gassy curd of the harmful +types is produced, knowledge is gained of the kinds of bacteria +present. + +According to Barthel, milks that reduce the methylene blue within +fifteen minutes contain hundreds of thousands of bacteria per cubic +centimeter. Those that require from fifteen minutes to one hour for +the disappearance of the color are also high in bacteria, and are to +be classed as a poor grade of market milk. If one to three hours is +required, the milk is comparatively low in bacteria, and is to be +classed as a good grade of market milk. When more than three hours +elapse before the disappearance of the blue color, the bacterial +content is low and the milk is to be placed in the highest grade. + +The time of reduction is only a rough index of the number of +bacteria present, but it gives a good idea of the keeping quality of +the milk, and of the conditions of production and handling. Of the +above tests the sediment and acid tests are more frequently used. + +=Examination of milk sediments.= In the modern municipal laboratory, +efforts are made to determine, as far as possible, the conditions of +production on the farms, by an examination of the milk in the +laboratory. The samples of milk are sedimented in a small +centrifuge, and an examination of the sediment made with the +microscope. The types of bacteria and the number of body cells found +is an indication as to whether any of the animals of the herd are +suffering from inflammation of the udder. The test also gives +information similar to the dirt test since the insoluble dirt will +be thrown down and will impart a color to the sediment. + +=Pasteurization of market milk.=.The spread of the pasteurizing +process as applied to market milk has been rapid. This has been due +to the recognition of the fact that only by this process can a safe +milk _i.e._, one free from pathogenic bacteria, be obtained. As +previously mentioned a small proportion of all human beings that +have suffered from typhoid fever become bacillus carriers. It is +impossible to examine all persons who may be concerned in the +handling of milk in order to ascertain whether they belong to this +dangerous and unfortunate class of people. + +The larger cities have also recognized the impossibility of +requiring the tuberculin test of all cattle furnishing milk. +Pasteurization remains the only safeguard, and it is probable that +within a short time all the larger cities will require the +pasteurization of all milk, except that produced under strict +supervision. + +As previously mentioned heating causes certain changes in milk. In +the treatment of market milk it is desirable to use as low +temperatures as will suffice to destroy the disease-producing +bacteria. It is fortunate that temperatures that will insure this +result have little effect on the milk. The temperatures now +recommended for pasteurization are as follows: + + 158 degrees F. for 3 minutes. + 155 degrees F. for 5 minutes. + 152 degrees F. for 10 minutes. + 148 degrees F. for 15 minutes. + 145 degrees F. for 18 minutes. + 140 degrees F. for 20 minutes. + +In actual practice the milk is heated to 145 degrees for 25 to 30 +minutes. The acid-forming bacteria are not completely destroyed and +the pasteurized milk as a rule will undergo the same type of +fermentation as raw milk. It is, however, deemed essential that all +pasteurized milk be sold as such; that it be delivered to the +consumer within twenty-four hours after pasteurization and that no +milk be pasteurized a second time. + +The continuous pasteurizing machines have the disadvantage that a +small portion of the milk passes through so quickly that all +pathogenic bacteria therein might not be destroyed, (p. 131). This +has led to the use of the "holding" process in which the milk is +heated to the desired temperature and then placed in tanks where it +remains at this temperature for any desired time. Every portion is +thus treated in a uniform manner. + +If the milk is bottled after pasteurization, there remains +opportunity for reinfection, possibly with typhoid bacilli. +Pasteurization in the final container, the bottle, is being +recommended. This is possible only when a special bottle is used +with a metal cap lined with paper. + +=Milk distribution.= Until within recent years in the cities and at +present in smaller towns, milk is largely retailed from cans which +are carried on the wagons or are kept in stores. This exposes the +milk to contamination from street dust and from the container +furnished by the consumer. It is well recognized that every utensil +with which milk is brought in contact adds more or less bacteria to +it, and the less milk is handled, the better will be its condition +when it reaches the consumer. Milk is now largely retailed in glass +bottles which are closed with pulp caps. In some cities the bottling +is mainly done in the country at the bottling station to which the +milk is brought by the farmers; or it may be shipped by the producer +to a distributing company, and all subsequent treatment, as +pasteurization and bottling done in the city. + +Milk plants are now generally equipped for the rapid and economical +handling of large quantities of milk in a most sanitary manner. The +bottles as they are returned from the consumer are washed in a +continuously-acting automatic washer which washes, rinses and +sterilizes the bottles without their being removed from the cases in +which they are carried on the wagons. These machines are effective, +if not run at too rapid a rate, so that the bottles are not exposed +for a sufficiently long period of time to sterilize them. The +bottles are then filled and the paper caps inserted by machinery. +The caps can now be obtained from the manufacturers in sealed +tubes in which they have been sterilized so that the contamination +from this source is avoided. The shipping cans are washed and +sterilized with live steam, and in many plants are thoroughly dried, +by passing hot air into them. Under these conditions they then reach +the farmer with none of the musty and disagreeable odor that +frequently is present when the can contains a small quantity of +water, condensed from steam. + +The top of the milk bottle over which the milk is poured is exposed +to contamination from the hands of the deliveryman. Trouble from +this source can be avoided if the consumer cleans the lip of the +bottle before removing the cap. The better grades of milk are +dispensed in bottles, the top of which is protected by an additional +cover of paper or tin foil which reaches to the neck of the bottle +and is held in place by a crimped metal band. + +=Milk supply of the small cities.= It is true that the quality of milk +supplied to the large cities by the great milk companies is +generally much superior to that sold in the smaller cities and +villages. Many of the smaller places are however, attempting in +various ways to improve their supply. It is evident that methods +will be successful here that can not be employed in the larger +places. A detailed and careful farm inspection by a tactful, capable +inspector, coupled with proper publicity will do much to improve +conditions. The publication of the scores of the different farms, +and the demonstration of the sediment test as applied to their +product attracts favorable attention to the good dairies and +unfavorable attention to the poor. This usually has an effect on +the trade sufficient to cause the negligent producer and dealer to +improve. + +It is also becoming recognized that high grade milk can be produced +with very simple equipment. In fact the small farm is often more +successful in producing high grade milk than is the large farm on +which the work must be done by hired help for here the personality +of the owner can not make itself felt as where the producer is doing +a portion of the work about the barn and dairy himself. It is +becoming more and more evident that the chief factor in the +production of clean milk is the personality of the producer; he +should be one who gets enjoyment out of his clean stables and cows +and his high grade product. + +The man who is producing milk for the city market is but one of many +and his individual efforts can not make themselves felt. The +dairyman who is marketing his own product is in a position where his +efforts to produce a fine product should prove of distinct advantage +to him in enabling him to sell it for a higher price than that +obtained for ordinary milk. + +It should be remembered that the production of clean, healthful milk +is not a question of equipment, but of methods and of additional +work. The cows must be fed, the stables must be cleaned, the cows +milked, and the milk delivered to the consumer. If beyond this +unavoidable labor a small additional amount is expended, the +improvement in the product will be great. It is necessary that the +additional work be placed where it will do the most good, in keeping +the cows clean both summer and winter so that little need be done in +cleaning them before milking, the pails and other utensils kept +clean and sterilized, and the milk cooled as soon as possible and +kept cold until delivered to the consumer. The delivery should be +made within the shortest practicable time after the milk is drawn. +In order that the healthfulness of the milk may be beyond question, +the herd must be kept free from tuberculosis and some attention +should be paid to the health of the men, especially with reference +to whether they may be typhoid carriers or not. The necessary labor +should not increase the cost of the milk over one cent per quart. It +has been shown in many cases that such a product can be marketed at +a price that will more than compensate for the additional cost. +Clean, fresh, rich milk is being sold in villages and small cities +located in the great butter and cheese producing sections of the +country for eight to ten cents per quart. + +=The duty of the consumer.= The educational campaign that has been +carried on by the health departments with reference to farm +conditions and methods of handling has been most effective in +improving the milk supply. Many cities are now extending this to the +consumer, recognizing that as much harm may be done in the home as +on the farm. The importance of keeping the milk cold, of not +allowing it to stand exposed in open vessels, of thoroughly cleaning +the vessel in which it is kept, or the milk bottle before returning +it to the milkman are especially emphasized. + +Moreover, it must be impressed upon the consumer that all of these +improvements, not only on the farm where the milk is produced, but +in the hands of the distributing companies in the cities, involve +much expense, and cannot be carried out, unless the consumer is +willing to pay their cost. More objection seems to be raised over +an increase in the price of milk than any other food stuff. The +consumer therefore needs education along the line of higher prices +for milk. Dairy products of all types have increased much in value +in recent years, so that at present prices milk, sold directly as +milk, is relatively cheaper than in any form, when prevailing prices +are compared with those that obtained a decade ago. + + + + +INDEX. + + +Abnormal fermentations, overcoming of, 108. + +Abortion, contagious, 75. + +Acid, amount of formed in milk, 84. + +Acidity test, 211. + +Actinomycosis, 75. + +Aeration of milk, 55. + +Aerobic bacteria, 13. + +Air, contamination of milk from, 51. + +Alcohol test, 213. + +Alcoholic fermentation, 96. + +Anaerobic bacteria, 13. + +Animal, contamination of milk from, 42. + +Anthrax, 75. + +Antiseptics, 16, 117. + + +B. + +Bacillus Bulgaricus, 89, 101. + +Bacillus lactis acidi, 86. + +Bacteria, aerobic, 13; + anaerobic, 13; + culture media for, 20; + desirable acid-forming, 86; + determining number of, 22; + distribution of, 18; + effect of cold on, 14; + effect of heat on, 15; + food of, 12; + forms of, 8; + manner of growth of, 9; + movement of, 11; + nature of, 8; + parasitic, 11; + products of, 17; + pure cultures of, 25; + rate of growth of, 13; + relation to air, 13; + relation to chemicals, 16; + relation to drying, 15; + relation to light, 16; + relation to temperature, 12; + size of, 9; + saprophytic, 11; + spores of, 10; + types of acid-forming, 86; + undesirable acid-forming, 90. + +Bedding, 47. + +Bitter fermentation, 97. + +Bleaching powder, 112. + +Bloody milk, 99. + +Butter, bacteria in, 154; + bacterial defects in, 156; + cowy odor in, 157; + deterioration of, 155; + fishy, 157; + metallic, 157; + molding of, 157; + preservatives in, 155; + putrid, 156; + source of flavor, 140; + turnip flavored, 156; + types of, 137. + +Butter-milk, 100. + +Butyric fermentation, 93. + +Boric acid, 117. + +Borax, 117. + + +C. + +Carbolic acid, 111. + +Cheese, abnormal fermentations of, 174; + bitter, 177; + Camembert, 186; + Cheddar, 164; + colored, 178; + flavor production in, 172; + gassy, 174; + Gorgonzola, 185; + Limburger, 187; + moldy, 179; + preservation of by acid, 171; + putrid, 178; + quality of milk for, 162; + ripening of, 169; + Roquefort, 184; + Stilton, 185; + Swiss, 180; + temperature of ripening, 173; + types of, 161. + +Children, diseases of, 80. + +Chloride of lime, 112. + +Cholera, 80. + +Cleaning utensils, 39. + +Clean milk, production of, 53. + +Cold, effect of, on bacteria, 14. + +Colored milk, 98. + +Condensed milk, 135. + +Contagious abortion, 75. + +Contamination of milk, from milking machine, 50; + in factory, 59. + +Cooling of milk, 54. + +Corrosive sublimate, 111. + +Cream, control of fermentation of, 142; + pasteurization of, 146; + ripening of, 138; + separators, 36. + +Cresol, 111. + +Curd test, 104. + +Cycle of fermentations, 99. + + +D. + +Deodorants, 109. + +Digestive fermentation, 93. + +Diphtheria, 79. + +Dirt, exclusion of, 44; + removal of from milk, 53. + +Disinfectants, 16, 109. + +Disinfection, 109. + +Distribution of bacteria, 18. + +Dried milk, 135. + +Drugs, excretion of in milk, 58. + +Drying, effect of on bacteria, 15. + + +E. + +Emmenthaler cheese, 180. + +Evaporated milk, 134. + + +F. + +Factory by-products, 36; + treatment of, 38. + +Feeds, effect of on milk, 57. + +Fermentation test, 104. + +Fermented milks, 100. + +Fly, contamination of milk by, 60; + means of spreading typhoid fever, 78. + +Foot and mouth disease, 74. + +Fore milk, 31; rejection of, 34. + +Formalin, 112. + + +G. + +Galactase, 172. + +Garget, 75. + +Germicidal action of milk, 33. + +Gorgonzola cheese, 185. + + +H. + +Hairs, bacteria on, 43. + +Heat, effect on bacteria, 15. + +Heated milk, detection of, 39. + +Hydrogen peroxide, 118. + + +K. + +Kefir, 102. + +Koumiss, 102. + + +L. + +Lange Wei, 95. + +Light, effect on bacteria, 16. + +Limburger cheese, 187. + +Lime, 110. + +Lumpy jaw, 75. + + +M. + +Malta fever, 75. + +Market milk, municipal regulations concerning, 190; + pasteurization of, 214. + +Milk, acid fermentation of, 83; + aeration of, 55; + affected by feed, 57; + alcoholic fermentation of, 96; + bacterial standards for, 206; + bitter fermentation of, 93; + certified, 202; + butyric fermentation of, 93; + certified, 202, 208; + clarifying of, 115; + condition of when secreted, 29; + contamination of from animal, 42; + from by-products, 36; + from utensils, 34; + contamination of with tubercle bacilli, 67; + cooling of, 54; + creaming of, 136; + culture medium for bacteria, 28; + cycle of fermentation in, 99; + distribution of, 216; + digestive fermentation of, 93; + dirt in, 44; + effect of heat on, 119; + filtration of, 114; + germicidal action of, 33; + grades of, 201; + guaranteed, 201; + inspected, 202; + miscellaneous fermentations of, 98; + pasteurization of, 120; + pasteurization of in home, 131; + preservation of by antiseptics, 117; + preservation of by cold, 116; + relation to children's diseases, 80; + ropy fermentation, 94; + sediments, examination of, 214; + selected, 203; + slimy, 94; + spontaneous fermentation of, 91; + sterilization of, 134; + straining of, 153; + supply of small cities, 217; + sweet curdling fermentation of, 92; + tainted, 56, 58; + temperature standards for, 208; + tests for quality of, 209. + +Milk pails, sanitary, 48; + small topped, 48. + +Milker, factor in contamination of milk, 51. + +Milking-machines, 36, 50. + +Mold on butter, 177; + on cheese, 179. + + +O. + +Odors, absorption of, 56, 58. + +Oidium lactis, 186. + +Oleomargarine, 152. + +P. + +Pasteurization, 120; + efficiency of, 133; + purpose of, 123; + methods of, 125. + +Pasteurized milk, fermentations in, 124. + +Pasteurizing machines, tests of, 130. + +Process butter, 152. + +Ptomaine poisoning, 81. + +Pure cultures, 25. + + +R. + +Rabies, 75. + +Reduction test, 213. + +Rennet, 170. + +Ropy fermentation, 94. + +Roquefort cheese, 184. + +Rusty spot in cheese, 178. + + +S. + +Salicylic acid, 117. + +Scarlet fever, 79. + +Score card for dairies, 198. + +Sediment test, 210. + +Skim milk, heating of, 38. + +Slimy fermentation, 94. + +Spores of bacteria, 10. + +Stalls, 46. + +Starters, 143; + for cheese, 167; + propagation of, 146. + +Sterilization, 21, 134. + +Stilton cheese, 185. + +Storch test, 39. + +Straining of milk, 33. + +Sulphur, 111. + +Sweet curdling of milk, 92. + +Swiss cheese, 180. + + +T. + +Taints, determination of cause of, 58, 103. + +Temperature effect on growth, 12. + +Tubercle bacilli, destruction of, 71; + in butter, 70; + in cheese, 70; + in milk, 67. + +Tuberculin test, 73. + +Tuberculosis, 64; + closed, 70; + distribution of disease in animal, 66; + economic aspects of, 72; + open, 70. + +Typhoid fever, 76. + + +U. + +Udder, inflammation, 75; + invasion of by bacteria, 30; + number and kind of bacteria from, 32; + structure of, 30; + washing of, 47; + cleaning of, 39. + +Utensils, contamination from, 34. + + +W. + +Water, effect on butter, 153; + supply, 59; + testing of, 60. + +Whey, heating of, 38. + +Wisconsin curd test, 104. + + +Y. + +Yeast fermentation, 96. + +Yoghurt, 101. + + + + + +End of the Project Gutenberg EBook of Outlines of dairy bacteriology, by +H. 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