Milk and its products; a treatise upon the nature and qualities of dairy milk and the manufacture of butter and cheese

Front matter

Edited by L. H. Bailbt

A TREATISE UPON THE NATURE AND QUALITIES OP

DAIRY MILK AND THE MANUFACTURE

Preface

The revolution in dairy practice brought about by the introduction of the centrifugal cream separator and the Babcock test for fat> and by a more definite knowledge regarding the .various fermentations that so greatly influence milk and the manufacture of its products, has seemed to demand the publication of a small handbook that shall give to the dairyman, and particularly to the dairy student, in simple, concise form, the principles underlying modern dairy practice. In attempting to meet this demand, I have had largely in view the needs of my own students, while still keeping in mind the general dairy reader.

In the collation of the information, where so many points are still unsettled, it is of course difficult in all cases to distinguish fact from conjecture. The aim has been at all times to give the present state of knowledge as supported by the weight of evidence and the opinions of those whose authority is highest. In how far this has been successful time alone can tell. It would be

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viii Preface

too much to hope that every conclusion will stand the test of further investigation and experience.

Dairy practice in the United States owes much to the investigations of the Agricultural Experiment Stations. Of the results of their labor free use has been made in various ways, and in many cases without specific mention at the particular place. Without wishing to make distinctions, particular acknowledgment is here rendered to the reports and bulletins of the Stations in Maine, New Hampshire, Vermont, Connecticut (Storrs), Canada, New York (State), New York (Cornell), New Jersey, Pennsylvania, Illinois, Iowa, Wisconsin and Minnesota. For those who wish to make more extended investigations, a bibliography is added in the Appendix, giving references to many bulletins.

Thanks are due to D. H. Burrell & Co., the Vermont Farm Machine Co., the DeLaval Separator Co., the Star Milk Cooler Co., the Champion Milk Cooler Co., J. F. Hodgkin, and F. B. Fargo & Co., for the use of electrotypes.

Acknowledgment is also due my colleagues^ Messrs. Cavanaugh, Durand, Hall and VanWagenen, for valuable assistance, and to Professor L. H. Bailey for much friendly counsel and many useful suggestions.

HENRY H. WING.

Cornell. University Dairy, January 1897.

PEEFACE TO THE NEW EDITION

In the preparation of a new edition of Milk and Its Products, in addition to making such changes as are necessary to bring the body of the work up-todate, it has seemed well to add chapters on dairy cattle and the production of milk, on certified milk, and on ice-cream, manufacture. Brief directions for simple bacteriological determinations have also been added. The latter has been prepared by my daughter, Lois W. Wing, late assistant in dairy bacteriology, in the New York State College of Agriculture. The chapter on certified milk was written by Mr. George C. Watson, formerly manager of the Tully Farms, and grateful acknowledgment is hereby made to both for their assistance.

HENRY H. WING.

New York State College of Agriculture Cornell University, July, 1912

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CHAPTER I Secretion of Milk

Milk defined — Mammary glands — Udder — Internal structure of udder and teats — Ultimate follicle — Secretion of milk — Incentives to secretion — Amount and duration of flow — Effect of succeeding pregnancy — Incomplete renioval of milk — Regularity and frequency of milking — Control of animal over secretion.

CHAPTER II Composition of Milk

Milk constituents — Colostrum — Specific gravity — The fats — The volatile fats — The non-volatile fats — The albuminoids — The sugar — 'The ash — Other constituents — Variations in quality of milk.

CHAPTER III The Production of Milk — Dairy Cattle

Milk a maternal function — The cow the only commercial milk producer — Factors in the production of milk — The lactation period — The operation of milking — Relation of form to capacity — Value of records of production — ^^Necessity for keeping records — Food as a factor in milk production — The ideal ration — Selection of breed — Pure breds and grades— Maintenance of the dairy herd — Selection of the bull — Management of the bull — Grading up the herd — Major and minor dairy breeds — Jerseys — Guernseys — Holstein-Friesians — Ayrshires — Shorthorns — Red Polled — Brown Swiss — Dutch Belted — Devons,

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xii Contents

CHAPTER IV The Testing of Milk

Gravimetric anaylsis — History of milk tests — Cream gauges — Specific gravity — Lactometers — Churn tests — Lactobutyrometer — Pioscope — Lactoscope — Soxhlet's Method — Lactocrite — Fjord's control apparatus — Milk tests in the United States — Short's method — Method of Failyer and Willard — Parsons' method — Iowa Station test — Cochran's method — Babcock test — Beimling test — Gerber's method — Butyrometer — Details of Babcock test — The centrifugal machine — -The glassware — Sampling the milk — Composite sampling — Making the test — The acid — -Whirhng^ — Reading — Cleaning the glassware.

CHAPTER V The Ferments and Fermentations of Milk and Their Control

Tendency to undergo change — Germs of fermentation — Bacteria — Presence of bacteria in milk — Kinds of bacteria in milk — Fermentations of milk — Relation of milk bacteria to the human system — Lactic fermentations — Fermentations affecting the albuminoids — Butyric fermentations — Control of fermentations — Prevention of infection — Holding at low temperatures — Destruction of germs in milk — Pasteurization — Selection of milk for pasteurization.

CHAPTER VI Determination of Bacteria in Milk

Bacteria as a measure of dirt in milk — The laboratory — Apparatus — Media — Sterilization — Cleaning glassware — Procedure for plating — Checks.

CHAPTER VII Market Milk

Milk for consumption — Cleanliness — Treatment after drawing — Aeration — Delivery — Bad flavors in milk — Quality of milk for consumption — Control of milk supply — Cream for consumption — Pasteurized cream — Quality of cream.

Contents xiii

CHAPTER VIII Certified Milk

Definition — Origin of certified milk — Standards — Production — Sanitary stables — Selection of the cows — Care of the cows — Care of the stable — Milking — Care of utensils — Cost of production.

CHAPTER IX Separation of Cream

Gravity creaming — Shallow-pan creaming: — Deep setting system — Centrifugal separation — Conditions affecting completeness of separation — Conditions affecting the relative amount of skimmed milk and cream — Contrivances in the bowl to increase the efficiency of separation — Mechanical conditions affecting separation — Efficiency of separation in centrifugal machines — Desirable and undesirable features of a separator.

CHAPTER X The Ripening of Cream

Means of producing lactic acid — Temperature of ripening — Amount of acid necessary — Acid tests — Determination of lactic acidin milk and cream — Further effects of ripening — Churning cream of different degrees of ripeness — Bad effects of over-ripening.

CHAPTER XI Churning

Viscosity of the milk — Ripeness of cream — Temperature — Nature of agitation — Quality of the globules of fat — End of churning — Difficult churning.

CHAPTER XII Finishing and Marketing Butter

Washing the butter — Working — Salting — Brine salting — Packing and marketing — Composition and quality of butter.

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CHAPTER XIII Milk for Cheese Making

Theory of cheese making — Quality of milk for cheese making — Loss of fat — Cooling — Aeration — Ripening — Rennet tests — Degree of ripeness necessary — Starters — Rennet — Removal of whey.

CHAPTER XIV Cheddar Cheese Making

'Setting — Cutting — Heating — Cheddaring — Grinding — Salting — Curing — Difficulties likely to occur in cheddar cheese making — Qualities of cheese.

CHAPTER XV Other Varieties of Cheese

Home-trade or stirred-curd cheese — Sage cheese — Young America — Picnics — Pineapple — Truckle — American Neuf chatel — Philadelphia cream cheese — Limburger — Imitation Swiss — Prepared cheese — Enghsh cheese — Stilton — Cheshire — Lanca- . shire — Derbyshire — Leicestershire — Wensleydale — Gorgonzola — Emmenthaler or Swiss — Edam — Gouda — Roquefort — Brie — Camembert — D'Isigny — Pont L'Eveque — Port du Salut — Parmesan.

Appendix

A. Useful rules and tests.

B. Metric system of weights and measures.

C. Legal standards for milk in the various states — The oleomar-

gerine law^The filled-cheese law— The New York state dairy law.

D. References to Agricultural Experiment Station reports and

bulletins.

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I

Udders of good and poor types.

From Bulletin No. 62, Purdue Univ. Agr. Exp. Sta., by permissioH.

See page 3.

Chapter I The Secretion Of Milk

The females of all animals that suckle their young (class Mammalia) secrete for this purpose a special fluid which is known as milk. It is an opaque yellowish white fluid, with a slight alkaline reaction and a faintly sweetish taste. It consists of an emulsion of fats in a watery solution of alkaline salts, casein and sugar. It is secreted in two special glands situated without the body cavity on either side of the median line, and known as the mammary glands or mammae.

Mammary glands. — While, strictly speaking, there are but two glands, each gland may be divided into two or more lobes, each having a separate opening ; thus, while there are ordinarily but two simple glands in the ewe, mare and goat, in the cow there are four or six, in the cat and bitch six to ten, and in the sow ten to fourteen. In animals having multiple glands, the mammae occupy nearly the whole of the lower part of the chest and abdomen. In ther animals the glands are confined either to the nest or abdomen. In many animals each gland A . (1)

or lobe is furnislied with a single opening connecting with a single duct, in others several ducts open independently upon the surface of a single nipple or teat. The mammary gland is a true organ of secretion in the sense that its product (milk) contains substances not before existing in the blood, that are formed during the process of secretion in the gland itself. In the cow the mammary glands are located on the posterior portion of the abdomen between the hind legs, and each gland is made up of two lobes or quarters, each having a single outlet furnished with a single duct, though there are often one and sometimes two rudimentary ducts upon the rear quarters, and which are occasionally developed to such an extent that milk may be drawn from them in small quantities. The whole organ is spoken of as the udder, and the ducts as teats. While the mammary gland is essentially a female organ, it is present in a rudimentary condition in the males of all mammals, and in exceptional cases in man and in the lower animals the organs of males have developed to such a degree as to secrete milk.

The cow^s udder. — The udder is enclosed in a fold of skin, which is here thinner and softer than upon other parts of the body, and is supported by a band of fibrous tissue that springs from the median line of the body and extends through the whole substance of the gland. It varies very much in size and shape in different animals and in the same animal at different times. Its size is not always an indication of the secreting powers of an animal, since the numstructure of the Udder 3

ber of true secreting follicles does not necessarily bear any relation to the apparent size. The udder in a good cow should be large and well developed ; it should occupy the whole space between the hind legs, extending well up between the thighs and well forward upon the belly. It should be held firmly against the wall of the abdomen. It should be level or nearly so on the bottom, and the four quarters should be as nearly as possible equally developed and each furnished with a cylindrical perpendicular teat of moderate length. The whole organ should diminish rapidly in size as the milk is withdrawn. The hair upon the udder should be fairly abundant, fine and soft, and abundantly supplied with a brownish dandruff.

The substance of the udder is composed of the fibrous band, already mentioned, connective tissue, fatty tissue, milk ducts or canals, true secreting cells (acini, ultimate follicles, alveoli), veins, arteries, nerves and lymphatics, the whole making up a reddish gray mass of spongy texture.

The udder varies very much, in different individuals, in size and shape as well as- in internal structure and secreting capacity. In some animals the amount of connective and fatty tissue is much larger than in others. Such udders are said to be "fleshy," and while usually of large size and good shape, are deficient in true secreting capacity. They are firm to the touch, particularly when empty, and do not markedly diminish in size when the milk is withdrawn. It is generally supposed that such udders are more subject to inflammations and inflammatory diseases than those with less fatty tissue. In many cows the fibrous net -work that supports the udder is held firmly up to the under side of the abdomen. If, in connection with this, the udder has comparatively little connective and fatty tissue, the animal will have an udder apparently small, but with large capacity for secretion. In old cows, particularly those that have been large milkers, the fibrous bands often become largely relaxed, so that the udder falls nearly to the ground, and appears to be of enormous size.

Internal structure of the udder and teats. — The teat is simply a canal surrounded by muscular walls and closed at the extremity by an involuntary sphincter muscle, which varies much in rigidity in different animals ; often it is so lax that the pressure of a small amount of milk in the canal is sufficient to open it and the animal leaks her milk. In other animals it requires a strong effort of the hand to draw the milk. When desirable, the rigidity may be overcome by keeping a smooth wooden plug of sufficient size to moderately dilate the opening in the end of the teat till the muscle relaxes sufficiently to permit easy drawing of the milk, or the muscle may be partially divided with the knife in the hands of a skilful operator. At the top of the teat, or bottom of the udder, there is a small cavity known as the milk cistern, serving to hold the milk after its secretion until it is drawn. It is of varying capacity, up to half a pint,

Arrangement of Milk Ducts 5

and is partially separated from the canal of the teat by a more or less well - marked constriction in the muscular walls of the upper part of the teat. From the milk cisterns a system of canals or so-called milk ducts extends to all portions of the udder. These ducts are larger near their opening into the milk cistern, and diminish in size as they rise through the udder. They branch and anastomose freely in all directions, and finally end in a group of small sac -like bodies, the ultimate follicles. The system of milk ducts arising from each teat is practically distinct, though there is more or less communication between the smaller ducts in the upper portions of the two quarters on the same side of the animal. This renders it possible to draw a part of the milk secreted in the hind quarter from the forward teat on the same side, and vice versa. There is no communication between the ducts on opposite sides of the animal. At the junctions of the larger ducts there are greater or smaller enlargements, forming small cavities or milk reservoirs, which serve the same purpose as the reservoirs at the top of the teat. The branching points of all the ducts, large and small, are guarded by sphincter muscles. These muscles are connected with the abdominal muscles of the animal, and she is able to more or less completely close them at will, and so "hold up" her milk. It requires a strong effort on the part of the animal to completely close the larger ducts in the lower part of the udder ; a comparatively slight effort is all that is necessary to close the smaller vessels. Animals vary greatly both in the control they possess over these muscles and in their disposition to use it. Very few can completely close the larger ducts, and very many rarel}' exercise whatever power they do possess. Sudden fright, the presence of strange persons or animals in the stable, any irregularity in the time or manner of feeding or milking, and slight feverish conditions, particularly sexual heat, are the most common provocatives to holding up milk. There are very many cows that contract the habit of holding up the milk upon the slightest provocation, and if the habit is once formed it is almost impossible to cure it, and the result is that the usefulness of the animal as a milk producer is largely destroyed, for the retention of the milk in the udder interferes greatly with the activity of secretion, and in a short time permanently lessens it.

The ultimate follicles. — The milk ducts, after branching and anastomosing in all directions, finally end in a group of small sac -like bodies known as acini, or ultimate follicles. It is in these small bodies that the secretion of the milk takes place. They are about l-30th of an inch in diameter, and are found in groups of three to five, with a common outlet at the end of each branching duct. In form and appearance they present marked changes according to the condition of the animal. During active lactation they are found in their highest development. When lactation ceases, the

Secretion of Milk 7

smaller ducts become much retracted, and the follicles shrink in size and finally become rudimentary, or even entirely disappear, until under the stimulus of a succeeding pregnancy, the whole gland renews its activity, and the ducts and follicles regain their former size and appearance. New ducts and follicles may also be formed up to about the fifth or sixth year, and the power of the animal to secrete milk be thereby increased. Surrounding the follicles, and intimately attached to them, are capillary blood vessels, both veins and arteries, and through the cells of the membranes making up the walls of all these vessels the fluids of the blood freely pass into the cavity of the follicles by means of osmosis, or transudation. The cavity of the follicle is lined with epithelial cells, that during lactation are filled with protoplasm, and are capable of rapid multiplication, growth, and degeneration, at the same time that the cell contents are undergoing rapid and extensive changes.

The secretion of milk. — The milk is formed from the blood, partly by the transudation of the blood serum directly into the cavity of the milk follicle, and partly by a transformation of the contents of the epithelial cells lining the cavity of the follicle, which at this time are especially active. The water passes directly from the capillaries into the milk follicles and ducts, carrying with it the mineral constituents in solution and a part of the albumin of the blood serum; but by far the larger pai't of tlie albumin is in some way changed during its passage from the capillaries, and appears in the cavity of the follicle as the casein of the milk.

Fig. 1. Section tlirough alveoli of the mammary gland of the dog in first and second stages of secretion. From Meade Smith, after Heidenhain.

When milk is being secreted, the lining cells of the follicle are in a state of constant activity. New cells are constantly being formed by budding or fission (the cell elongates, a partition forms across it, and the tw^o halves so divided enlarge to the size of the mother cell, and there are two cells where but one existed before), and older cells are as constantly breaking down. While this is going on, the cell contents, consisting m^ainly of protoplasm, become changed into a globule of fat, and the globules so formed are either extruded through the cell wall into the cavity of the follicle, or set free by the breaking down and reabsorption of the cell wall. In all probability both processes take place. Small portions of the fat may also be carried over directly from the blood and appear in the milk without change. The milk sugar is probably formed

Incentives to Secretion 9

through a chemical change in the contents of these lining cells, since but minute quantities of sugar are found in the blood.

Incentives to secretion. — Maternity is the prime incentive to the secretion of milk. While there is a distinct increase in the development of the mammae upon attaining puberty, it is not until pregnancy is well advanced that the organ attains anywhere near its full development, or that there is any activity in the true secreting cells. In the virgin animal, and up to within a short time of parturition, the cavities and ducts of the udder contain a watery saline fluid, but true milk does not appear until a short time before, and in some cases not until after, parturition. The immediate stimulus to the production of milk is the turning of the blood that went to nourish the foetus from the arteries of the uterus to the arteries of the udder. The pressure of blood in the vessels of the udder stimulates the secreting cells to great activity, and the cells, hitherto dormant, begin to multiply rapidly. When this activity is first set up, the various processes of secretion are more or less incomplete, so that the milk first se creted is very different in character from that secreted afterwards, and is known as colostrum. The colostrum contains in the first place considerably less water than^ normal milk; in the second place, the transformation of albumin into casein is only partial, so that colostrum contains large amounts of albumin; and finally, when secretion of milk begins, the cells of the follicle multiply more rapidly than they can be reabsorbed, and portions of partially broken down cells break away from the walls of the follicle and appear in the colostrum. Gradually the colostrum takes on the character of normal milk, and in the course of four or five days the change is complete. Other characteristics of colostrum are discussed in detail in the next chapter.

While maternity is the prime cause of secretion, it is not the only means of stimulation to the activity of the udder, nor is it a necessary prerequisite to the secretion of milk. The regular removal of the saline fluid in the gland of the virgin animal, or even the stimulation of the organ by the friction of the hand or the suckling of a calf, may be sufficient to cause the secretion of milk of normal character in considerable quantities. In the same way and under the same exciting causes, other glands of the body, notably the lymphatics in the arm pits and the rudimentary mammae of males, have been known to secrete a fluid resembling milk in all essential characteristics.

Amount and duration of flow. — With wild animals in a state of nature, the milk is secreted only in amount sufficient for the needs of the young animal, and only until the young is sufficiently developed to secure its food independently of the motTier. Under the influence of domestication the cow has been brought to increase her flow of milk many fold, and the time during which it is secreted has been lengthened until it is almost, and indeed is, in some cases quite continuous. A dis-

Dependence upon Circulation of Blood 11

cussion of the agencies by means of which this most important result has been brought about would open up the whole question of the selection, breeding and training of cows, as well as everything pertaining to the science of foods and feeding, which is not here possible. There are, however, some physiological conditions affecting the secretion of milk that may be mentioned.

Milk is secreted from the blood. The amount of milk secreted will, therefore, depend upon the amount of blood passing through the udder, and this, in turn, will depend upon the number and size of the blood vessels, not only in the udder itself, but leading to it and away from it, the vigor of the cii'culation, the supply of food to the animal, and her capacity to eat, digest and assimilate it and turn it into blood. From or shortly after parturition, there is a constant tendency of the blood vessels in the udder to shrink in size, and consequently a constantly diminishing flow of milk. When the period of lactation advances at the same time that the pastures are growing more scanty and less succulent, this diminution is fairly regular and constant, especially after from three to five months of the period of lactation have passed. This tendency to shrinkage in the size of the blood vessels of the udder may be held in check in great measure by an abundant supply of nutritious food, particularly if it is of a succulent character, and it is not at all uncommon to find cows secreting milk in regular amount, or "holding out," for eight or ten months. But in this respect the individuality of the animal plays an important part, so that wide variations are seen in different individuals under the same conditions of food and care. After a shrinkage in the flow has once taken place, it is extremely difficult to again increase it by increased food until after another calving.

Effect of succeeding pregnancy. — The effect of the animal again becoming pregnant is to decrease the flow of milk. The cause of this decrease seems, in many cases, to be two-fold: First, a sympathetic effect, following immediately upon conception, and secondly, a shrinkage due to a turning away of a part of the blood from the udder to nourish the growing foetus. This shrinkage does not become marked until the fourth or fifth month of pregnancy. In this respect, as in their power to "hold out," individual animals show the widest variation. With very many the effect of becoming again pregnant is so slight as to be scarcely noticeable ; with others it is so great as to materially interfere with the usefulness of the animal.

Incomplete removal of milk. — One of the most important means of checking the secretion of milk lies in the incomplete removal of milk already secreted. We have already seen that the removal of the saline fluid from the ducts of the inactive gland is an efficient stimulus to secretion. So, too, the presence of milk in the ducts acts as a check to further secretion. Further than that, it not only checks secretion but is an actual irritant, suffi-

Regularity of Milking 13

cient in many instances to give rise to inflammations of a serious character. Clean milking is . one of the most nnportant aids in keeping up and prolonging the flow of milk.

Regiilarity and frequency of milking. — While the process of milk secretion is a continuous one, it is not entirely uniform. There is reason to believe that the secretion is considerably more rapid while the operation of milking is going on, and that a considerable portion of the whole amount is then secreted. On the other hand, the distension of the milk ducts and reservoirs by milk already secreted acts as more or less of a check upon the activity of the follicles, and so lessens the rapidity of secretion. While for these reasons it would be inferred that frequent milking would lead to increased secretion, the limits of such increased secretion are' moderate, and beyond a certain point no increased flow of milk is secured by increasing the frequency of the milking periods. In all cases where the udder becomes unduly distended with milk between periods, an increased flow will be secured by milking oftener. The common practice is to milk twice in the twenty -four hours, and the nearer the time can be divided into equal periods the more uniform will be the secretion. Where more frequent . milking is practiced the same principle will hold. Not only is regularity in the period from morning to night of importance, but regularity in the time of milking from day to day is equally so. A difference of an hour in the time of milking will frequently make a difference of 10 per cent in the amount secreted, and where these irregularities are frequent, will soon result in a considerably diminished flow. The amount of milk given is also considerably affected by the way in which the milk is drawn. In general, it may be said that rapid milking is conducive to a large flow. In any event, the milk should be drawn so that no discomfort is caused the animal, and in this respect there is great difference in milkers. A rapid, uniform stroke, with a firm touch on the teat, and a stroking motion to the lower part of the udder, gives the best results. Babcock has found that certain milkers uniformly get not only more but richer milk from the same cow. Control of the animal over secretion. — The secretion of milk is involuntary. The animal can no more control it than it can control the respiration or the circulation of the blood. Yet there are numerous conditions of the animal that have a more or less direct effect upon the secretion of milk. These conditions have not only to do with the physical condition of the animal — as the supply of food, the circulation of the blood, extremes of temperature, etc. — but extend in large measure to the nervous organization and condition of the animal. We have already seen that the animal may by an exercise of will more or less completely control the withdrawal of milk already secreted ; so, too, there are nervous conditions that have a great effect upon the actual secretion. Sudden fright, an unfamiliar milker or attendant, unusual excitement, sexual excitement, or the presence of an animal in heat in the herd, an