Cow's milk, whole, or with part, or all of the cream removed, and evaporated to dryness, is variously named dry milk, desiccated milk, dehydrated milk, pulverized milk, milk powder, powdered milk, or milk flour. Sometimes it contains sucrose, and sometimes alkali or a buffer salt is added to render the product easily soluble. Powdered milk is well dried. Troubles due to bacteria and enzyme action are seldom met with, but deterioration due to oxidation of the milk fat may take place. For this reason milk powder from skimmed milk is most extensively manufactured.
The Public Health (Dried Milk) Regulations 1923 prescribe for the labelling and description of dried milk and milk powder. There are four classes of dried milk (I) dried full cream milk; (2) dried three-quarter cream milk; (3) dried half-cream milk; and (4) dried quarter-cream milk. Such milk shall contain not less than the following percentage of milk fat and milk solids :— Utilization of Milk.—The percentage of the total annual milk production used for various purposes remains fairly constant. The following table shows quantity of milk, and percentage of production used for each purpose in 1936: The following table shows the annual per capita consumption of milk, butter, cheese, evaporated and condensed milk, and ice cream for the period 1927-36.
City Milk Supply.—The smaller American cities, having pop ulations from a few hundred to 5,000, are usually supplied en tirely by farmers who live near the cities, and by people who live in the suburbs and own one or more cows. Cities with a popula tion of 5,000 to i o,000 are supplied by farmers from near the cities and also by milk distributors who purchase milk from more distant farmers and distribute it throughout the city. The larger cities receive their milk supply by train or truck from the country districts, sometimes from a distance of 200 or more miles. The supply of cream may be furnished in part by dairy districts soo to i,000 m. distant. The farmers who supply milk for such large cities as New York and Chicago, receive a price based on the butter-fat content of the milk less a charge for transportation according to the zone from which it is shipped. The zones are 10 m. in width and shippers in the same zone pay the same transportation costs per ioo lb. of milk. Milk receiving and cool ing stations are located along the railroads, to which the milk is delivered direct by the farmers or "milk haulers" who collect from the farmers. Milk is hauled by passenger trains or by special trains which take precedence on the railroad over most of the other traffic. When the milk arrives at the depots it is speedily taken to the plants of the milk distributors, pasteurized, cooled and bottled ready for the milk wagons or trucks to deliver it to the consumers the following day.
Milk ordinances differ greatly in detail requirements, depending on local conditions. In general, however, the milk ordinance gives the local board of health the power to inspect the sanitary con ditions on the farms and in the plants, and to otherwise super vise and control the milk supply. Even when all precautions are taken to insure that the milk c,omes only from healthy cows, how ever, or that it is handled only by healthy people, there is always the possibility that certain harmful organisms may gain entrance in one way or another. Many city boards of health do not con sider it wise, therefore, to permit the sale or distribution of raw milk for direct consumption, and they require that the milk supply be pasteurized as an additional means for safeguarding the health of the people.
Milk is pasteurized to kill any disease-producing organisms that may be present; if the process is performed properly it makes the milk entirely safe for consumption and does not af fect its flavour or nutritive properties. Pasteurization is now re garded favourably by most physicians, sanitarians, dairymen, and consumers. As a result there is a constantly increasing trend toward pasteurization throughout the United States. In 1939 more than 8o% of the milk supply in cities of 75,000 population was pasteurized. The percentage increased as the size of the cities increased, and very little raw milk is now sold in the largest cities. In the smaller towns and villages, however, only a small pro portion of the milk is pasteurized.
The pasteurization of milk for direct consumption, as applied under commercial conditions, means a process of heating every particle of milk to a temperature not lower than 542° F. for not less than 3o minutes (holder process), or to a temperature not lower than 560° F. and holding at that temperature or above for not less than 15 seconds (short-time, high-temperature process). After the milk is pasteurized, it is cooled immediately to so° F. or lower. The holder process of pasteurization is the method most generally used today. Some cities prohibit the use of the short-time, high-temperature process. (L. S. R.) MILKING MACHINE: see DAIRY MACHINERY.
the name applied to two South American trees. In Brazil this is Mimusops elate, which produces a latex that "exudes in abundance when the bark is cut ; it has about the con sistence of thick cream" (A. R. Wallace, Travels on the Amazon and Rio Negro), and is used as milk and as glue. The timber of this tree is valuable and the fruit is edible. It belongs to the sapodilla family (Sapotaceae). The milk-tree of Venezuela is Brosimum Galactodendron, a member of the mulberry family (Moraceae). (See COW-TREE.)