87% 3.3% 5% 4% .7% The protein in milk is casein and albumin, in the pro- portion of about six to one. The casein is precipitated by the presence of acid, as when lactic acid is formed in the souring of milk. The ferment rennin, found in the stomach of milk-drinking animals, also causes coagulation of the casein. The albumin is coagulated by heat. The carbohydrates of milk are in solution in the form of lactose, or milk sugar. A part of this is changed to lactic acid by the action of the bacteria that cause milk to sour. The fat in milk is held in suspension in the form of minute globules, so finely divided that as many as ten billion may be contained in a single drop. These gradually rise to the surface, forming cream. The mineral salts include all those found in the animal body, such as lime, phosphates, potash, and others. (86) PROTEIN— 311 L[<: 87 Food Value. — Milk is a complete food, since it contains all the food principles, and therefore builds and repairs tissues and gives heat and energy. It serves much the same purpose to the young of animals as the egg does to the unhatched chick. The large amount of water in milk is useful for the young in building and filling out the tissues. For an older person, however, milk contains too much water and not enough carbohydrates; about five quarts a day would have to be consumed to supply the body needs. Yet milk is really a concentrated food, since fully a third of the solid portion is protein and another third is fat. These nutrients are in such finely divided form as to be very easily digested. This is especially true when milk is taken along with other foods. Milk should be sipped slowly, and the greatest benefit is derived when taken at regular inter- vals or at night before retiring. Souring of Milk. — As has been explained, milk is soured by lactic acid produced by bacteria. When milk is warm the bacteria increase very rapidly, thus hastening souring. The acid separates the protein (casein) from the water and forms the curd (the thick part) , leaving the whey (the liquid part). The whey contains, besides water, nearly all of the milk sugar, which gives to it its chief food value. Clean fresh milk carefully handled to exclude dirt, should keep sweet for several days. Adulteration of Milk. — The fat is so valuable for cream or butter that sometimes much of it is removed before the milk is sold. The commonest method of adulteration is to add w^ater, and, unless a great deal is added, is hard to detect. What is worse, chemical preservatives are sometimes added to kill bacteria or retard their growth, in order to keep the milk sweet and carry it great distances. The chemicals used are boric acid, formalin, and salicylic acid. S8 DOMESTIC SCIENCE These are very harmful, especially to infants, and conceal unclean methods of handling milk. Such milk can be detected when it does not sour easily or becomes thick and develops a bitter taste. State and national pure-food laws and city ordinances are gradually doing away with these abuses.

AI-modernized reading of the original text

87% 3.3% 5% 4% .7% The protein in milk is casein and albumin, in the proportion of about six to one. The casein is precipitated by the presence of acid, as when lactic acid is formed in the souring of milk. The ferment rennin, found in the stomach of milk-drinking animals, also causes coagulation of the casein. The albumin is coagulated by heat. The carbohydrates of milk are in solution in the form of lactose, or milk sugar. A part of this is changed to lactic acid by the action of the bacteria that cause milk to sour. The fat in milk is held in suspension in the form of minute globules, so finely divided that as many as ten billion may be contained in a single drop. These gradually rise to the surface, forming cream. The mineral salts include all those found in the animal body, such as lime, phosphates, potash, and others. (86) PROTEIN— MILK 87 Food Value. — Milk is a complete food, since it contains all the food principles, and therefore builds and repairs tissues and gives heat and energy. It serves much the same purpose to the young of animals as the egg does to the unhatched chick. The large amount of water in milk is useful for the young in building and filling out the tissues. For an older person, however, milk contains too much water and not enough carbohydrates; about five quarts a day would have to be consumed to supply the body needs. Yet milk is really a concentrated food, since fully a third of the solid portion is protein and another third is fat. These nutrients are in such finely divided form as to be very easily digested. This is especially true when milk is taken along with other foods. Milk should be sipped slowly, and the greatest benefit is derived when taken at regular intervals or at night before retiring. Souring of Milk. — As has been explained, milk is soured by lactic acid produced by bacteria. When milk is warm the bacteria increase very rapidly, thus hastening souring. The acid separates the protein (casein) from the water and forms the curd (the thick part) , leaving the whey (the liquid part). The whey contains, besides water, nearly all of the milk sugar, which gives to it its chief food value. Clean fresh milk carefully handled to exclude dirt, should keep sweet for several days. Adulteration of Milk. — The fat is so valuable for cream or butter that sometimes much of it is removed before the milk is sold. The commonest method of adulteration is to add w^ater, and, unless a great deal is added, is hard to detect. What is worse, chemical preservatives are sometimes added to kill bacteria or retard their growth, in order to keep the milk sweet and carry it great distances. The chemicals used are boric acid, formalin, and salicylic acid. These are very harmful, especially to infants, and conceal unclean methods of handling milk. Such milk can be detected when it does not sour easily or becomes thick and develops a bitter taste. State and national pure-food laws and city ordinances are gradually doing away with these abuses.

Domestic science, principles and application