Fig. 14.—Apparatus for Cooling Milk.
Certified Milk.
—Dairies which are inspected either by operation of the law or, voluntarily, by a competent body of medical and scientific experts duly authorized to make such inspection furnish to the market what is known as certified milk. Each bottle of this milk bears the stamp of certification and this stamp may be used from the time of one inspection until a certain date specified on the stamp when the next inspection takes place. The duty of the inspectors is to see that diseased animals are at once removed from the dairy, that the sanitary conditions of the stable are perfect, that the food is abundant and wholesome, that the milking process is conducted according to the principles above outlined, and that the proper precautions are taken to prevent infection during the preparation of the milk for the market. The milk should be examined chemically and bacteriologically at each inspection, or oftener, to see that it is of a standard quality, both in respect of the number and character of the organisms which it contains and of its chemical constituents. Certified milk is, of course, more expensive than non-certified, inasmuch as the dairy is necessarily called upon to bear the expense of inspection. However, the superior quality of such milk and its certain freedom from infection more than offsets the increased price, and makes certified milk the ideal food of a milk character, not only in the family, but especially in the hospitals, orphan asylums and other public institutions. It seems quite certain that in the near future practically all the milk that is sold upon the market of the country will be of a certified quality.
Pasteurized Milk.
—When milk is heated to a temperature of about 140 to 160 degrees the greater part of the living organisms contained therein are destroyed. At the same time the temperature is not high enough to give to the milk that peculiar taste which it acquires when boiled. Such pasteurized milk, placed in sterilized bottles, stoppered with sterilized stoppers and kept in a cool place, will keep many days and even weeks without apparent deterioration. Physicians and hygienists are quite agreed that pasteurized milk is not so wholesome, especially for children, as certified milk which has not been subjected to a heat sufficiently high to kill the organisms contained therein. The natural ferments of the milk, namely, the enzymes which produce the lactic fermentations, promote rather than interfere with the digestion of the product. The killing of the beneficial organisms of the milk is only justified when there is danger of pathological germs being present. Hence the pasteurization of milk must in this sense be regarded as a substitute for inspection and certification.
There may arise cases where pasteurizing even of certified milk may be desirable, namely, when from necessity it must be kept for a considerable period before use, as on shipboard, and other places inaccessible to a daily supply of fresh milk. Pasteurizing is also justifiable in miscellaneous milk supplies, the origin of which is unknown. It is safer, by far in this case, to pasteurize than take the chance of consuming pathological germs.
Pasteurizing of Milk.
—A convenient method of pasteurizing milk is recommended by the Dairy Division of the Department of Agriculture, which is as follows:
Directions for the Pasteurization of Milk.
[20]—The pasteurization of milk for children, now quite extensively practiced in order to destroy the injurious germs which it may contain, can be satisfactorily accomplished with very simple apparatus. The vessel containing the milk, which may be the bottle from which it is to be used or any other suitable vessel, is placed inside of a larger vessel of metal, which contains water. If a bottle, it is plugged with absorbent cotton, if this is at hand, or in its absence other clean cotton will answer. A small fruit jar loosely covered may be used instead of a bottle. The requirements are simply that the interior vessel shall be raised about half an inch above the bottom of the other, and that the water shall reach nearly or quite as high as the milk. The apparatus is then heated on a range or stove until the water reaches a temperature of 155 degrees Fahrenheit, when it is removed from the heat and kept tightly covered for half an hour. The milk is rapidly cooled without removing it from its containers and kept in a cool place. It may be used any time within twenty-four hours. A temperature of 150 degrees maintained for half an hour is sufficient to destroy any germs likely to be present in the milk, in cold weather, or when it is known that the milk reaches the consumer soon after milking, and it is generally safe to adopt this limit. It is found in practice that raising the temperature to 155 degrees and then allowing the milk to stand in the heated water for half an hour insures the proper temperature for the required time. If the temperature is raised above 155 degrees the taste and quality of the milk will be affected.