All About Milk
( Originally Published 1904 )
PRACTICALLY, in speaking of milk, we have in mind cow's milk. But it must be remembered that in some countries the milk of other animals is used as food; as that of goats, of asses, and of mares. The latter is used in the preparation of fermented milk, known as Koumiss, which is properly a medicine rather than a food. ,
We have already considered milk as to its essential constituents, caseine, butter, sugar of milk, and salts. There are a few other proper-ties which it is useful to know about.
Milk is an article of food which changes with remarkable facility. Even when handled with the greatest care, it carries in it germs from the air which cause it to undergo quickly a remarkable modification. Under the action of the ferment of sour milk-it becomes more and more acid because a part of the sugar of milk is transformed by this germ into lactic acid. When the quantity of acid has reached a certain limit, this acid coagulates the caseine and causes the cheese of the milk to pass from a liquid state to that of solid particles. We say then that the milk is curdled or sour. This acid fermentation is more common at the ordinary temperature than when near the freezing point. That is why milk curdles more easily in summer than in winter. This accidental souring of the milk is retarded by scalding the milk, for the heat kills the germ. But sometimes the effort to save the milk may only hasten the process when the quantity of acid formed is not sufficient to sour the milk when cold, but is sufficient to coagulate it when heated.
We can understand from this that in the art of cooking, milk does hot go well with an acid, or an acid food, especially if heated.
Milk gasses through another sort of coagulation: that which occurs shortly after its pas-sage into the stomach. The gastric juices of the stoach secrete an acid which is very likely t6 coagulate the Milk. This is . a perfectly natural phenomenon, and we are not justified in regarding such changes as accidents, or an indication of disordered digestion. For the first duty of a healthy stomach is to turn the milk which it receives. That is also why cheeseiakers use the " rennet," which is the fourth stomach of calves, to coagulate the milk to make cheese.
The rapid change which milk undergoes, and the danger which it may present as a means of communicating certain affections, such as tuberculosis, should invariably be met by sterilization. Much might be said upon this point, but, as the only means of sterilization that is practical in the kitchen is boiling, we will con-fine our attention to that form. This method of sterilization is very effective, provided that the process of boiling is continued for several minutes. When-the milk rises for the first time, the phenomenon is not due to boiling, but to the escape of gas, for the milk has not yet reached the boiling point, and the dangerous germs are not yet killed. It is then necessary to remove it from the fire and stir it, and then to replace it as soon as the foaming has subsided. It will be found that after rising several times it will settle down to a steady and quiet boiling.
There is 88 per cent. of water in good milk. .Yet it is a complete and perfect food for the new-born, provided that such receive the milk of its own species. The milk of the cow is three times as rich in albumen as the human milk. Hence we see the advisability of diluting cow's milk when fed to very young children. The milk of the dog is over five times as rich in albumen as the human milk, and that of the hare, seven times. These great differences explain the enormously rapid increase in weight of the young in their first days. Thus a child doubles its weight in 180 days; a calf in 47; a pup in 9; and a young hare in 6 days.
A great inconvenience of an absolute milk diet for an adult is the very large quantity of several quarts which 'would be needed. This would not become repugnant, but would fatigue the digestive tube.; but even if such diet could be borne it would be found that the subject would soon become pallid, weak, and sickly. Just why is not known, but it is evident that while it is a perfect food for the young, milk is unfit for the adult. Among the materials which it lacks must be mentioned iron. It is one of the weakest foods in this respect that are known. The new-born is adapted for this state of things, for he brings with him from the moment of his birth a supply of iron which he uses little by little (luring his period of nursing. Physicians are agreed that children which nurse for fifteen or eighteen months or two years, as is the custom in Russia and in Southern Europe, are unhealthy, flabby, anemic, and are long in walking.
In spite of these inconveniences milk is an important factor in our nourishment, since it supplies what would otherwise be deficiencies by its addition to other foods.
The digestibility of milk is in general very good. When a quart of milk was taken it was found that all of the sugar of milk was absorbed, and only 6 per cent. of the albumen and 4 per cent. of the butter escaped.