Care Of Milk

The importance of keeping milk clean cannot be over-emphasized. Aside from all esthetic considerations, absolute cleanliness is essential as a protection to health. Milk is an excellent culture medium for bacteria, and these organisms may not only be of types producing changes in the character of the milk, such as alterations in flavor, odor, color, decomposition of proteins, formation of gases, alcohol, lactic acid, etc., but also disease germs, especially those of tuberculosis, scarlet fever, typhoid fever, and diphtheria.

Commercially, care of milk is important as effecting the keeping qualities. For all these reasons, milk should come from a healthy animal in a sanitary environment. Milking must be done under conditions which protect the milk as fully as possible from contamination through impurities on the cow herself, on the hands or clothing of the milker, in the receptacles used for the milk, and in the air, in the place where the milking is done. Milk should be immediately cooled, and transported to the consumer in sealed bottles; cooling prevents the growth of bacteria. Such cautions necessarily increase the price of milk, but even then milk is a cheap food and the additional security is worth paying for.

Certification Of Milk

To insure a milk free from impurities, the method of certification and pasteurization have been widely adopted.

Certification involves a specific testing of milk against all accidental and harmful contamination. To secure it the services of chemists, bacteriologists and veterinary surgeons are required. The most vital object desired is the exclusion of tubercule bacilli from milk, which involves a special inspection of dairy herds and rejection of tuberculous cows. Other pernicious germs, pus corpuscles, etc:, are also sought for.

Certification of milk requires periodical inspection of dairies, of bottled milk bought in open market, etc. All milk must correspond to a number and variety of tests, too numerous to be mentioned in this connection. Every branch of the milk trade is covered. Such milk receives a certificate which should contain the date of milking and is naturally expensive, but it should be used whenever possible for infants and little children, and for all purposes in households which buy the best grades of other food materials.

Pasteurization

This is the process by which milk is rendered more or less sterile through destruction of active bacteria by heat. Various standards as to temperature and time have been adopted, but in general the milk is heated to a temperature not exceeding 167° F., for a period of 20 to 45 minutes, and then rapidly cooled to 45° P. or lower. Most harmful bacteria and lactic acid bacteria are killed. Spores are not killed, and if the milk is not kept cold or is allowed to stand too long, putrefactive organisms develop. These putrefactive changes are very undesirable, so that the care of pasteurized milk is just as important as that of fresh milk. If carelessly handled, the fact that it does not sour readily is a menace to health rather than a benefit.

Commercial pasteurization is a cheap and effective means of preventing the spread of ordinary infectious diseases. The degree of heat used does not change materially the flavor nor the chemical composition of the milk. It does destroy the enzymes naturally present in milk, and how much this affects the value of milk for infants is still unsettled. When clean fresh milk cannot be absolutely insured, it is safer to pasteurize. But this process cannot make bad milk good nor dirty milk clean. If bacteria have already produced poisonous products it will not destroy them.

Sterilization

Sterilization is accomplished by keeping milk at boiling temperature (212° F.) for 10 or more minutes, preferably in the vessel in which it is to remain. This will kill all living bacteria, but will not destroy spores. Hence to render milk absolutely sterile, repetition of the process on successive days is necessary. This is rarely done, as the spores are not likely to develop if the milk is kept at a temperature of 40° P. or less.

Sterilized milk is not an ideal food. Boiling changes the taste, the cream does not rise as quickly, and it is less easily coagulated by the action of rennet. Lecithin is decomposed, diminishing the amount of organic phosphorus compounds, and increasing the inorganic phosphorus which is not as useful to the body. The calcium salts are changed, and the ferments of the milk destroyed. Sterilization should be regarded as an emergency measure, for hot weather, when cooling facilities are lacking.