Page:The story of milk.djvu/77

 *ing melted butter-fat or oil mixed with water or skim milk through exceedingly small apertures under high pressure, or otherwise breaking up the mixture, an emulsion can be formed in which the fat globules are much finer even than those in natural milk or cream, and separation can be prevented. The force used in these emulsifiers may be produced by powerful pumps, or a steam jet, or centrifugal force under high speed; whichever system is used the machines answer the same purpose, to produce a permanent emulsion in which the oil or fat will stay in suspension even after cooling. In some milk supply plants and ice cream factories all the cream is emulsified and the system has especially been applied since the advent of the milk powder. It is now a not infrequent practice to run the new milk through the separator, make sweet, unsalted butter from the cream, and milk powder from the skim milk, and to ship or store these products separately where or until cream is wanted and then bring them together again by running them through the emulsifier with a suitable amount of water. At first thought this process would seem impractical and uneconomical. But it has proven good business because in many cases and places skim milk powder and butter keep better separately or can be shipped at long distance to better advantage than new milk or cream or condensed milk. In ice cream factories business may be dull in cold weather and cream is perhaps not provided and not available, when suddenly a hot spell brings orders for large quantities. With a stock of skim milk powder and butter on hand in the refrigerator, and an emulsifier to mix these products, cream can be produced on short notice and there will be no danger of shortage.