Milk is the natural food of the young mammal, and contains all the foodstuffs in a form easily assimilable. Starch is not present, the carbohydrate being found in the form of lactose, or milk sugar, a sugar differing somewhat from the sugars found in vegetables and fruit (see Chapter X (The Fats And The Sugars)).
Whole milk and the milk products, cream, butter, and cheese, are all important food materials among the nations of the western world; and the manufacture of milk products, such as condensed milk, butter, and cheese, has developed large industries. While the Chinese and Japanese are two great peoples who have not utilized milk or any of its products as food for grown people to any extent, yet we are fully justified in counting these foods among the necessities. Nothing can fully take the place of milk in the family dietary. Figure 41 shows how all the foodstuffs are represented in milk. When milk first comes from the cow the fat is suspended in tiny, invisible particles throughout the water, giving the milk its yellow tint, and the fat rises to the top in the form of cream after a few hours. The protein, sugar, and ash are dissolved in the water. When milk reaches the stomach, the protein separates from the water in the form of curd. This change is brought about by an enzyme (soluble ferment) called rennin, which is present, along with pepsin, in the gastric juice. Curd is also formed by the souring of milk through the action of bacteria, or by adding acid directly to the milk. Milk should never be gulped down, but taken in sips, so that only small portions of curd are formed in the stomach, because these are much easier to digest than large ones. Sometimes milk is soured purposely, as in buttermilk or zoolak or matzoon, that curds may form and be beaten fine before it is drunk. This is very easy to digest, because then no large curds can form. For the same reason, it is often better to take milk with bread or some other food, or to cook it in some dish. Skim milk is a valuable food, for it has everything found in whole milk but the fat. We miss the flavor of the fat in drinking it, hence it is better to use it in pudding or soup or in cooking cereals where we do not care so much about the milk flavor. Study Fig. 41, comparing the percentages of the foodstuffs in whole, skim, and buttermilk, and cream. Notice that the skim milk is higher than the whole milk in protein and sugar, that it has as much ash, and a trace of fat even. It does not tell us, however, that the forms of ash in milk are most valuable, and that it is richer in calcium than any other food material. How these foods compare in fuel value is shown in Fig. 42.
Fig. 41. - Composition of milk and cream.
At present, the milk supply is one of our most pressing community problems, showing
Fig. 42. - 100-Calorie portions of milk and cream.
Weight of Portion, ounces
Cream (18.5% fat).................................
how closely the country and the city are united. A case of typhoid fever in one farm family, not properly cared for, may be the seed of a serious epidemic in some town. To insure clean milk to the consumer, and a fair return in money to the producer, is a great sanitary and commercial problem, not to be solved in a day.
Milk is a medium in which bacteria flourish, both the harm-less and the disease producing. Typhoid fever and other fatal diseases may be carried by milk from unclean barns and dairies, and tuberculosis is possible from diseased cows. The cows must be in good health, and the stable clean. Figure 43 shows a stable with cement floor and good drainage. The cows must themselves be clean, and should be curried and washed. The milkers should have clean clothes and hands, and all receptacles should be sterilized. The milk must be rapidly cooled (see Fig. 44), bottled in sterilized bottles, kept cool during transportation, and delivered as promptly as possible to the consumer. "Certified" milk is produced and handled under the best conditions, but costs at least 15 cents a quart. Since a quart of milk is equivalent to a pound of steak or to 8 eggs, milk even at 15 to 20 cents a quart is more economical than meat and eggs at ordinary prices. At the usual price of 8 to 10 cents a quart, milk is very economical as compared with other perishable foods.
Fig. 43. - A modern cow house.
The question of preservation and pasteurization can be treated here but briefly. Preservatives are forbidden by law in most states. Pasteurization is heating at a temperature sufficiently high to kill any disease germs present, but not high enough to give a cooked taste. This process, while it destroys most of the bacteria, does not kill the spores of all. The chief arguments against pasteurization are (1) that on a commercial scale it is difficult to really accomplish this, and (2) that it is easily used to cover the sale of unclean milk. The argument for it is, that it is impossible to obtain as yet an ideal supply for a large city in hot weather, and that pasteurization, if properly conducted, kills nearly all of the dangerous bacteria and saves the lives of many babies. Clean milk that needs no pasteurization is our ultimate aim, and we must remember that milk pasteurized under unknown conditions needs to be kept cold and treated with even more care than fresh milk, for it "spoils" quite as easily, only we may not know it because it may not taste sour. In the last few years the question of pasteurization has been studied with very great care. It is found best to heat the milk for 20 to 30 minutes at a temperature of 140° to 155° F. If it is certain that this method has been used, one need not hesitate to trust the milk, for the arguments against pasteurization do not properly apply here.
Fig. 44. - Milk bottling room.