CANNING, REFRIGERATION and ICE MANUFACTURE.
W. Wiley, Foods, their Adulteration, ManufacBibliography.-H. W. Wiley, Foods, their Adulteration, Manufac- ture and Composition (3rd ed., 1918) ; A. J. Wallis-Tayler, Refrigera tion (6th ed., 192o) ; W. G. Savage, Canned Foods in relation to Health (Camb. Univ. Press, 1923) ; S. C. Prescott and B. E. Proctor, Food Technology (1937) . Much information as to methods of drying and storing is also contained in the Reports of the Food Investigation Board published yearly by H.M. Stationery Office and in the Report of the Committee of the Departmental Committee on Preservatives in Food. (H. E. C.; J. A. To.) Concentrated Milks are among the most important preserved foods and are extensively used. Nearly 700,000,000lb. entered in ternational trade in 1936, according to the U.S. Department of Commerce. Of a total world production of about 3,000,000,000lb., approximately 6o% is manufactured in the United States, where about 2S3,000,000lb. of sweetened condensed milk, about 2,000, 000,000lb. of evaporated milk, and about 400,000lb. of dried milk were produced in 1937. Sweetened condensed milk denotes milk from which a considerable portion of the water has been re moved, and to which sugar has been added. Milk is rapidly heated to effect destruction of bacterial life; sucrose is added; and the milk is condensed in a vacuum until 21 parts of whole milk are reduced to one part of condensed. It is cooled and placed, usually, in small tin containers, although also distributed in bulk. Con- , densed skim milk is likewise manufactured. Evaporated milk, of j unsweetened condensed, is somewhat similarly made, but without sugar. Milk is forewarmed, condensed under vacuum, and before cooling, homogenized. It is canned and then heated for a suffi cient period to cause complete sterility.
Dried or powdered milk was first made by Grimwade in Eng land in 1855. It is prepared commercially by several methods. In the spray process pre-condensed pasteurized milk, under high pressure, passes through fine apertures into a steel chamber at 27o° F. The water evaporates and the resulting powder is re moved from the bottom of the chamber. In the roller process fox drying milk pre-heated milk is poured upon hot steel drums or cyl inders. More dried skim milk is manufactured than is dried whole milk. Malted milk, marketed since 1887, is a powdered product made from whole milk, whole wheat, and barley malt. Evaporated milk is a sterile product, while condensed and dried milk are gen erally low in bacteria, although not sterile. The sucrose in con densed milk inhibits the growth of bacteria and moulds. Patho genic bacteria which might be present in the whole milk are de stroyed by the various manufacturing processes. Except for vita mins B 1 and C, heating for concentration does not appreciably affect the vitamins of the whole milk. Vitamin C is not present in evaporated milk, and is apparently somewhat reduced in con densed and dried, though there is evidence that spray process dried milk retains most of its content of this vitamin. Other nutritive qualities are not appreciably affected. The canned concentrated milks are stable and will keep for considerable periods of time in the unopened package. (J. A. To.)
