The Story of Milk

DAIRY CATTLE

A number of typical but widely different breeds of dairy cows have been developed in various dairy countries, each owing to the soil and the climatic conditions of its home, as well as to the skill and fancy of the breeders, its characteristic features, form, color, etc.

Milk-Breeds.—The black and white Holstein-Friesians (which, by the way, had their home in Holland and not in Holstein) are known for their large production of not very rich milk, while the Guernseys and Jerseys give milk exceedingly rich in butter-fat. A good Holstein cow will give from 7,000 to 10,000 lbs. of milk in a year, containing from 3¼% to 4% butter-fat. Some of them produce as much as 20,000 to 30,000 lbs. in a year—nearly 4,000 gallons—just think of it! Jersey cows will usually not produce as much in quantity as the Holsteins but Jersey milk often contains 5% or 6% or more butter-fat, and a few of the best have been known to produce 800 to 900 lbs. of butter in one year, an amount equal to the cow’s own weight. The red Danish cow is an exceedingly good and highly bred milk producer which, however, has not been introduced in the United States, but the Scotch Ayrshires and the Brown Swiss are other well-known dairy breeds which are in favor with many American farmers.

But, alas! too many herds of dairy cattle average less than 5,000 lbs. of milk per cow per year and do not pay for their feed.

Many native cows respond, however, to good care and feed and with a thoroughbred bull a satisfactory herd can readily be built up from carefully selected native stock. Such continued cross-breeding is more apt to succeed than attempts to cross two thoroughbred breeds because the characteristic features in full-blooded animals are so strong as to invariably predominate in the progeny over the less pronounced forms and tendencies inherent in native cows. But where two full-blooded animals are mated and the strong characteristics in each are fighting for predominance the result is apt to be a poor, ill-proportioned offspring as the result of atavism.

Beef-Cattle.—Cattle bred and developed for the purpose of producing beef rather than milk are called by contrast beef-cattle. As examples of beef-cows look at the Shorthorns or the Herefords or the Polled Angus at the next State Fair you visit and notice the square, deep, smooth body with muscles and fat strongly developed in contrast to the loosely built, bony milk-cow with its tendency to turn all its food into milk at the expense of the body. There are, however, also among the Shorthorns, strains of good milkers, but as a rule these beef-breeds are not selected for the dairy farm, and “dual purpose” cows are not usually profitable.

Food and Water.—The natural food for the dairy cow in summer is grass, and where rich, succulent grass and clover grow in abundance, as on the fertile meadows of Holland and the Channel Islands, or the Swiss Alps, the highly cultivated Danish farms, the eastern and middle-western states of America, etc., dairying early reached its highest development. As the value of milk and its products for human food became more generally recognized and all-the-year-round production was forced, it was found necessary to feed the cows heavily in winter too, not only hay, but also grain and succulent food such as beets and corn-ensilage (green corn cut, stalks, cobs and all, and packed in a silo), and science was taken into play to formulate Balanced Rations containing the proper amounts and proportions of the various nutrients—Protein, Fat and Carbohydrates. It is not the place here to go deeper into this problem which has long been a subject for thorough research and experiments. In fact, more attention has been paid to the feeding of cattle than to the proper nourishment of human beings, and much of what we know about the latter has been deducted from experience and study on the dairy farm, and from laboratory work along that line. In the chapter on “Milk as a Food” we are taking up food values, etc., in relation to the feeding of children and men. Suffice it here to say that the same fundamental principles apply to the feeding of calves and cattle for the production of milk and beef. And we wish to emphasize the fact that, with due consideration to the proper proportion between the various groups of nutrients, it is much more important that the food is succulent, appetizing and easily digestible than that the ration shall be accurately balanced.

This fact, long well known to practical breeders and dairymen, has recently been confirmed by Dr. E. V. McCullom to whose experiments further reference is made in the chapter on milk as a food for children. He shows that there is a very great difference in the quality of Protein and Fat from various sources and that there is “Something Unknown” in butter-fat, for instance, which is absent in most other fats and which is vital for the growth of the child as well as for the proper nourishment of man. This unknown but essential substance is also found, in small quantities, in the leaves of certain plants, as in alfalfa, while it is absent in the grain of the cereals.

In modern dairy farming alfalfa is considered an indispensable source for protein, and corn-ensilage or beets for carbohydrates, while bran, cottonseed meal or oil cake, malt-sprouts, gluten, distillers’ grain, etc., may be used to advantage in various combinations.

Contrary to a general impression one cannot feed fat into the milk. A large amount of oil cake or other food rich in fat in the daily ration does not increase the percentage of butter-fat in the milk. Rather, it depends largely upon the breed and to some extent upon the period of lactation. Provided the food agrees with her digestion and keeps the cow in a good, healthy condition, the composition of the milk is not changed to any appreciable extent by a change in make-up of the food.

It goes without saying that to produce from 20 to 50 lbs. of milk a day the cow must have an abundance of fresh, pure water to drink and she should not have access to stagnant water.

The Barn must be clean, light and well ventilated and the cows should be milked with clean hands into a clean pail which is covered as far as possible so as to prevent dust from falling into the milk, or with one of the excellent milking machines which are now frequently used in large dairies. The milk is strained and cooled immediately after milking.

Milking.—The cows are usually milked twice a day; occasionally, when the highest possible yield is desired, as in important tests, three or four times. The first five days after the birth of the calf the milk,—the Colostrum so called,—is not normal and should not be used for human consumption. It may be fed to the calf. The first three to four months the yield of milk generally is higher than later, when it gradually drops until after about ten months it stops altogether and the cow goes “dry” at least for some six weeks before dropping the next calf. The highest annual yield may be obtained by having the cows “come in” in the Fall or early Winter and feeding them well all Winter to keep up an abundant flow of milk. Then, when they come out on pasture in the Spring,—in the latitude of the Great Lakes about May 15th,—the fresh, rich feed will stimulate production and give it a fresh start so that the milk-pail may continue to be filled during the next few months and the shrinkage of the yield will not occur until the time when the pastures dry up. The cow will then go dry in the early Fall, when feed is scarce. Usually, however, the cows are allowed to “come in” in the Spring and the yield of milk begins to shrink in the late Summer with little or nothing in the Winter.

Test the Cows.—To ascertain if a cow pays for her feed the amount and the quality of the milk should be tested and computed for the year. If the milk from each cow cannot be weighed every day it may be done regularly once a month or preferably oftener. If it is weighed morning and evening once every ten days it is easy to keep the account by multiplying the number of pounds by ten and adding the totals for the year. Occasionally the milk may be subjected to the Babcock Test to ascertain its richness; three or four times during the period of lactation is sufficient.

Where farmers do not have time to do the testing themselves they often combine and hire a young man or woman, trained in an agricultural college, to go around from farm to farm and do the work. These experts not only test the yield and the percentage of fat but also weigh and compute the feed so as to help the farmer make up his rations and calculate whether each cow pays for her feed or not. The members of these associations meet and compare notes and a friendly rivalry is stimulated which may do much toward increasing production. As a matter of fact, where Cow Test Associations have been introduced, both yield and quality of the milk have been largely increased.

Healthy Cows alone can be depended upon to produce sanitary milk. In many herds of milk-cows tuberculosis is prevalent, and constant vigilance is necessary to prevent its spread. The Tuberculin Test discovered by Koch is invaluable for the purpose of ascertaining the presence of tuberculosis. It is not necessary, however, to kill every infected animal. Only where the lungs or the udder is affected and a physical examination shows an advanced stage of the disease such radical means are advisable. When the tuberculin test was first introduced many valuable herds were wantonly and foolishly killed off because some of the highly developed dairy cows showed reaction to the test while worthless scrubs were allowed to live and spread the disease. For only the intelligent and public-spirited owners of fine herds submitted their cows to the test, a reaction to which, under ill-advised regulations, permitted state officials to condemn the infected herds. In Denmark Dr. Bernhard Bang introduced a system of isolation of the infected animals which together with Compulsory Pasteurization of the milk from such cows has proved efficient for the eradication of tuberculosis, and the Bang Method is now generally recognized as the proper way of handling the matter.

It consists therefore of 87% water and 13% “solids,” 4 of which are fat and 9, “solids—not fat.” Butter-Fat is found in milk in the form of minute globules suspended in the liquid. As fat or oil is lighter than water (has less specific gravity) it naturally floats and the fat globules therefore soon rise to the top when milk stands at rest, forming a layer of cream which may be skimmed off from the milk. In chemical composition butter-fat is very nearly the same as other animal and vegetable fats, but the slight variation may make a lot of difference in digestibility and palatability as well as in nutritive value, and it is a mistake to consider Oleomargarine, Butterine, Nut-Butter and other substitutes for butter “just as good” because a chemical analysis shows them to contain “almost” the same elements or compounds. These products may be good and legitimate if sold for what they are, but should never be allowed to be sold or served for what they are not, genuine butter.

Casein and Albumin are the proteids or nitrogenous matters of the milk, in chemical composition and in food value much the same as the protein in beans and peas or in meat, or the white of eggs. Casein is present in much larger quantity than albumin and is distinguished from the latter by being precipitated by rennet, which has no effect on albumin. Casein may also be precipitated by acids, while it required boiling as well as acidity to throw the albumin out of solution.

Milk-Sugar is related to the vegetable sugars, glucose, cane sugar, etc., and remains in solution in the whey which separates out from the cheese-curd when milk is curdled with rennet or acids. The whey also contains the mineral matters or ash, which consists largely of phosphate of lime, of use to the young in building up bones. When whey is boiled down to a thick syrup and left to stand, the sugar will crystallize out and may be separated from the liquid, still holding in solution the mineral matters.

Mineral Matters.—These may be gathered as ash by boiling off the water from this liquid or from the whole milk and burning the rest, as all the constituents except the ash belong to what in chemistry is called organic matter, which disappears in the air by burning.

HOW TO TEST MILK

Milk may be adulterated or decreased in value either by skimming or by watering. In either case the percentage of the most valuable constituent, the butter-fat, is diminished. It is upon this fact that the most practical test, the Babcock, is based.

The Babcock Test.^[2]—By treating a sample of milk with strong sulphuric acid the butter-fat is liberated as an oil. By subjecting the mixture to centrifugal force the light butter oil is separated from the rest of the milk and the percentage can be easily determined. Centrifugal force had already been used in the Fjord Cream Test, but it remained for Dr. Babcock to work out the splendid practical and reliable test which bears his name and in which he has given to the world an invention of incalculable value.

Sampling.—Whether it is new milk or skim milk or buttermilk or cream that is to be tested the first thing to observe is to take a truly representative sample. The liquid must be thoroughly mixed by pouring it several times from one vessel to another, or stirring vigorously.

It may not always be convenient to make a test immediately when the sample is taken. In the creamery where the milk is paid for according to its fat contents, samples are taken every day from every patron’s milk and it would take too much time for the butter maker to test all of these samples before they would spoil. A preservative, corrosive sublimate,—poisonous but all right for the purpose,—is therefore added and all the samples of one farmer’s milk for several days or a whole week are put together in one glass to be kept and tested at one time. This is called a composite test and has proven entirely satisfactory.

The Lactometer has been used to discover adulterations, depending upon the difference in specific gravity of the various constituents. The specific gravity of whole milk is about 1.032 which means that, if a certain volume of water weighs 1.000 weight units, the same volume of whole milk weighs 1.032, the same volume of butter-fat weighs, say, .900, or of cream about 1.000, and of skim milk 1.036 units. If the Lactometer shows a sample of milk to have a higher specific gravity than 1.032 it may therefore be suspected of having been skimmed. But it will readily be seen that by removing from whole milk some of the cream and adding water, the specific gravity can easily be brought back to normal for whole milk. This test is therefore unreliable and has been discarded with the advent of the Babcock.

Acidity Test.^[3]—The acidity, or sourness, of milk or cream, which depends upon the amount of lactic acid developed in it, may be tested by a liquid normal alkali or by the Farrington Alkaline Tablets, a solution of which added to sour milk neutralizes the acid. A few drops of an indicator, Phenolpthalein, added to the milk, turns it pink when all the acid has been neutralized, and the amount of alkali solution used shows the percentage of acid in the milk. This is quite important in preparing “starters” for ripening the cream in butter making or milk in cheese making, and in the manufacture of “Commercial Buttermilk,” etc.

There are other tests used in scientific dairying as the Fermentation Test to ascertain the relative purity of milk, the Casein Test, etc., but the above are those mostly used besides the Bacterial Count which is mentioned under the chapter on “Milk Supply,” and the Rennet Test described under “Cheese Making.”

FERMENTS

Two classes of ferments are of importance in connection with milk: (1) “unorganized” or chemical ferments, the “enzymes,” and (2) “organized” ferments such as bacteria and yeast.

Enzymes

Rennet.—Among the unorganized ferments, Rennet or Rennin is highly important on account of its power of coagulating or curdling milk by precipitation of the casein. Rennet is extracted from the stomach of the suckling or milk-fed calf, where it serves in digesting the calf’s food. It is in the market in the form of a liquid extract as well as a dry powder compressed into tablets (Rennet Tablets and Junket Tablets). The characteristics and use of rennet are described under “Cheese Making” in Chapter III.

Pepsin is another enzyme the office of which in the process of digestion is to dissolve albuminoids. It is not considered identical with rennet though in an acid solution it will curdle milk. It occurs in the stomachs of grown animals fed on solid food and is usually produced from hogs’ stomachs.

Bacteria

Everywhere, in the air, in water, in the soil, and clinging to every object in the world, are minute organisms known under the common names of bacteria or microbes. In contrast to rennet and the other “unorganized” ferments, bacteria belong to the “organized” class. Some are harmful, producing putrefaction, dissolution, poisons or disease; others are beneficial, leading to desirable fermentations and changes; others again are indifferent, neither good nor bad, but harmless.

As the milk comes from the cow it is almost free from bacteria, but milk makes an excellent soil for many of these organisms to grow in, and they soon get in, to multiply with enormous rapidity at any temperature from 60° to 100° F.

Lactic Acid Bacilli are bacteria of special importance to the dairyman, for they convert sugar of milk into lactic acid and produce various more or less agreeable flavors. They are also powerful germicides and scavengers, destroying or neutralizing the products of other bacteria which in the absence of these bacteria and the lactic acid produced by them would play havoc with the food and produce putrefaction or disease. Everybody who handles milk knows that pure sour milk or buttermilk in which lactic acid bacteria abound keeps well for a long time, free from other fermentations which have no chance to develop in their presence. It is due to this purifying property that Metchnikoff recommended Bulgarian sour milk as a health food, asserting that it prevents harmful fermentations in the digestive channel.

The Control of Bacteria

The principal means at our disposal to prevent or control and regulate bacterial growth are:

Cleanliness, Heat, Cold and Disinfectants.

Cleanliness.—Only the most scrupulous cleanliness will prevent contamination. Hence the necessity of thorough scouring and sterilizing of all utensils, and the need for fresh air and pure water.

Heat.—The prevention of fermentation in milk by heating is called “sterilization” or “pasteurization” according to the intensity of the heat and the length of time the milk is subjected to it. Boiling destroys almost all bacterial life. Some germs require, however, exposure to a much higher temperature, up to 250° F. (boiling under pressure), to be entirely eradicated, but for all practical purposes a thorough boiling is considered sufficient to eliminate all danger of contamination. Such boiling is usually termed Sterilization.

Cooling checks bacterial growth and but few germs thrive at a temperature below 50° F. The following table and diagram^[4] show how quickly bacteria multiply in milk at ordinary room temperature, 68° to 70°, which emphasizes the importance of keeping milk cool.

If the milk had contained 1,000 bacteria per cubic centimeter at the beginning, the part held at 50° F. would have contained 4,100 bacteria at the end of 24 hours, while that held at 68° F. would have contained 6,128,000. The effect of temperature upon the growth of bacteria is shown graphically in the cut.

But even frost does not kill the bacteria. If milk which has been kept sweet or at the desired degree of sourness by cooling is allowed to get warm again, the bacteria which have been kept dormant will get a fresh start. For this reason milk and cream for city supply should not only be cooled strongly, but must be kept thoroughly chilled up to the time they are used, which means that they should be delivered cool to the consumer, and kept on ice in the house, never being allowed to warm up until used.

Disinfectants.—Antiseptics, such as benzoate of soda, formalin, boracic acid, etc., are not permissible in milk, but disinfectants such as soda, lime, washing powders, etc., should be freely used in cleaning utensils, bottles, floors and walls where milk is handled, so as to prevent as far as possible any infection.

PASTEURIZATION

Pasteurization depends upon the fact that almost all bacteria, and especially the disease-producing species, are checked in their growth and made harmless, if not totally destroyed, by instantaneous exposure to a temperature of 175° F., or a more or less prolonged exposure to lower temperature, for instance for 20 minutes to 157° or 30 minutes to 145°. These lower temperatures are recommended in the case of new milk to be consumed as such, in order not to change its digestibility. Pasteurizers with “holding devices” are therefore largely taking the place of the “continuous” sterilizing machines, which allow only momentary exposure to the highest temperature.

Whatever method is used it is essential that after the heating is finished the milk should be cooled as quickly as possible to a temperature sufficiently low to prevent development of the germs that have not been entirely destroyed by the heat and which, if the milk is left for any length of time at a temperature favorable for bacterial life—anywhere between 65° and 110°,—will begin to grow again. Cool the milk to below 60° and if possible to 50° or 40°.

Sometimes a second pasteurization is practiced, the milk being purposely allowed to stand at 70° to 80° for 12 to 24 hours after the first pasteurization for the germs which escaped destruction to develop into full-grown bacteria. They are then killed by the second heating before the milk is finally chilled to stop any further growth.

Pasteurization can be done by placing the milk in any tin or enamelled or glass vessel, set in another vessel containing water (a double boiler). Heat until the milk has reached the desired temperature, hold it at that temperature the necessary time, and then place the vessel in cold running water or in ice water until the milk is thoroughly chilled. It is not advisable to place the hot milk in the ice box as cooling in air is too slow. Not until it is thoroughly cooled in water is it safe to put it in the ice box to keep it cool.

In the seventies Prof. N. J. Fjord, in Denmark, applied to milk the process which had been developed by Louis Pasteur in France to give keeping quality to wine and beer. A Danish dairy expert, J. Moldenhauer, now connected with the New York State Department of Agriculture, first brought the process to this country and used pasteurization in a city creamery in Kentucky. American experiment stations established the temperatures and the time of exposure necessary for best results, and no one has done more for the introduction of pasteurization than the New York philanthropist, Nathan Straus, who has established pasteurizing plants and milk distributing stations in many localities, thereby contributing so largely to the lowering of the death rate among the children of the poor.

The following directions are given by the Straus Pasteurized Milk Laboratories of New York for the pasteurization of milk for babies:

1. Only use fresh, filtered milk, which has been kept cold, and proceed as follows:

2. Set the bottles, after they have been thoroughly cleaned, into the tray (a), fill them to the neck, and put on the corks or patent stoppers.

3. The pot (b) is then placed on a wooden surface (table or floor) and filled to the three supports (in the pot) with boiling water.

4. Place tray (a), with the filled bottles, into the pot (b), so that the bottom of the tray rests on the three supports, and put cover (c) on quickly.

5. After the bottles have been warmed up by the steam for five minutes, remove the cover quickly, turn the tray so that it drops into the water. The cover is to be put on again immediately. This manipulation is to be made very quickly, so that as little steam as possible can escape. Thus it remains for twenty-five minutes.

6. Now take the tray out of the water and cool the bottles with cold water and ice as quickly as possible, and keep them at this low temperature till used.

7. Before use, warm the milk—in the bottles—to blood heat. Never pour it into another vessel.

8. The milk must not be used for children later than twenty-four hours after pasteurization. Never use remnants.

In a Continuous Pasteurizer a constant stream of milk is fed into the machine, heated by flowing over a metal surface with steam or hot water on the opposite side, and cooled by running over a cooler furnished with a stream of cold water or ice water.

PURE CULTURES

Before 1890 it was supposed that the flavor of fine butter depended upon certain volatile oils and acids peculiar to butter-fat. In the early nineties Professor V. Storch of the Danish Experiment Station showed, however, that it was due rather to the products of bacteria and he isolated the lactic acid bacilli which would produce such exquisite flavor even when perfectly neutral and tasteless butter-fat was churned with milk acidified or ripened with a pure culture of these bacilli. In this country Dr. H. W. Conn of Wesleyan University, Storrs, Conn., did much to advance the theory and practice of ripening cream with a pure culture starter.

“Pure cultures” are produced in the bacteriological laboratory by picking out under the microscope colonies of the desired species of bacteria, planting them in a sterilized medium and allowing them to grow under the most favorable conditions and with the exclusion of all other germs.

When such a culture has reached its maximum growth it is transplanted into a larger quantity of a sterilized medium containing proper nourishment for the particular organism. In the bacteriological laboratory, where alone absolute sterility of utensils and medium, and entire exclusion of foreign infection are possible, the culture may remain pure while this inoculation and propagation are repeated over and over again. But when the propagation is carried on in the house or the dairy, for instance in preparing starters or buttermilk, such absolute cleanliness is impossible and in the long run infections will creep in from the air or from the utensils and after a while it becomes necessary to start with a new “pure culture.” How often such renewal must be resorted to depends largely upon the surroundings and the care of the operator. Usually it must be done after a week’s time, although it is surprising to find milk preparations made by the simplest processes equal in purity to those prepared with the assistance of bacteriological science and technique. This is, for instance, the case in Bulgaria, where the famous Yoghourt sour milk is prepared pure without special care and in Denmark where the country is fairly permeated with the lactic acid bacilli used in ripening the cream for the celebrated Danish butter and where careful buttermakers often maintain their starters for months or even for years without “renewal.”

There are many different varieties of bacteria which convert sugar of milk into lactic acid, at the same time developing flavors more or less agreeable and characteristic for the various products. In the bacteriological laboratory certain species are selected which will produce the results desired for the particular purpose in view.

Starters.—Beginning with a commercial dry culture in the form of a powder as generally used in the creamery or the cheese factory as well as for the preparation of commercial buttermilk, or with buttermilk tablets as used in the ordinary household or the hospital, such culture is added to a small quantity of thoroughly pasteurized milk. If fresh, sweet skim milk is available it is preferable to whole milk as the butter-fat in the latter only interferes with the process; but either can be used.

Milk for starters should be strongly pasteurized by being kept at a temperature near the boiling point—at least 180°—for 40 to 60 minutes, then cooled to the degree at which it is to be set, usually between 65° and 75°, somewhat higher for the first propagation with the pure culture than for the subsequent transplantings when the bacteria, more or less dormant in the dry powder or tablets, have attained full vitality. Some species of bacteria, as the Bacillus Bulgaricus, require higher temperatures—90° to 100° or even 110°—than others. The culture having been thoroughly incorporated in the milk by vigorous and repeated stirring or shaking, the milk is left at rest in an incubator or a waterbath or wrapped in paper or cloth in a warm room where an even temperature can be maintained, until it is curdled, which may take 18 to 24 hours or even longer for the first propagation.

One part of this curdled milk is now added to 5 or 10 parts of fresh pasteurized milk and set to ripen in the same way as described above, possibly at a little lower temperature, and this is repeated every day, thus maintaining the “Mother Starter.” After the second or third propagation the bulk of each batch is used as a starter in the larger lot of material to be ripened, be it cream for butter or milk for cheese or for commercial buttermilk, while a little is taken for maintenance of the mother starter as described above.

The amount of starter to prepare every day depends upon the amount of milk or cream to be ripened and the per cent of starter used in same. For instance, if you have ten gallons of cream to ripen every day in which you wish to use about 10% or 12% starter, or one gallon, take a little less than one pint of the first or second propagation for one gallon of milk; the next day use one pint of this to add to a gallon of fresh starter milk, and the remaining gallon to add to the ten gallons of cream, and so on every day.

If you have 4,000 lbs. of milk in the cheese vat to ripen with 2% or 80 lbs. starter, prepare 88 lbs. of mother starter. If, on the other hand, you wish to make only a quart of buttermilk every day, take, say, two buttermilk tablets, crush them thoroughly in a spoonful of pasteurized milk and stir this into a tumblerful of the same milk; let stand till it is thickened the next day and use a tablespoonful of this thickened milk in a quart of fresh pasteurized milk which when ripened is your buttermilk, from which you take out a tablespoonful for starter in the next batch, and so on. In this case there is no “mother starter” except that perhaps the first tumblerful prepared with the tablets may be called so, but afterwards the starter is taken right out of the finished product every day.

The process may be modified to suit special purposes and local conditions, but the following precautions should be strictly observed: (1) to interrupt the ripening immediately by quick and intense cooling as soon as it has reached the proper point in case the ripened product is not used at once, and (2) to keep it ice-cold until it is used. If this is done, it may be kept for two or three days without deterioration if it is not convenient to make it fresh every day which, however, should be the rule.