Effects of Temperature and Time of Sterilization upon Properties of Evaporated Milk

Abstract

The effects of high-temperature -short-tinle heating of milk and of its concentrate on the heat stability of the concentrate have been described in recent publications (7, 8). The work reported here deals with the high- temperature-shor t-time ~ sterilization of concentrated milk in its relationship to some of the properties of the evaporated product and compares these properties with those of evaporated milk made in the conventional manner. METHODS AND EQUIPMENT The source of milk, the standardization of the milk to a fat to solids-not- fat ratio of 1: 2.29, forewarming, high-temperature heating, condensing, homog'enizing, pilot sterilizing and cooling were as described by Webb, Bell, Deysher and Hohn (8). New facilities included means for aseptically packaging the high-short sterilized milk. They are described by Curran, Bell and Evans (2). Viscosity measurements were made with a MaeMichael viseosimeter and the values converted to centipoises. All measurements were made at 30 ° C., the first within 3 days after the nlilk was sterilized. In preparing controls, the sterilizing temperature was 115 ° C. (239 ° F.) and the hohling time 18 mimltes. The sterilizing efficiency of the high-short process for evaporated milks was determined by pretreatment inoculation of the milk with washed spores of suitable heat resistance followed by incubation or subculture of the heated samples (2). Some of the high-short sterilized evaporated and the unsterilized control concentrates were canned and heated in a pilot sterilizer at 115 ° C. for various periods, cooled in a few minutes and stored at 30 ° C. with the other samples. The methods of measuring color were those used by Webb and Hohn (9). RESULTS The influence of the forewarming treatment, solids content and steril- izing conditions on the heat stability, viscosity and color of evaporated milks made from well-mixed portions of the same raw milk are shown in table 1. The forewarming treatment had a striking effect on the heat stability of the samples. A forewarming treatment of only 65 ° C. (149 ° F.) for 10