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High Temperature-Short Time Sterilized Evaporated Milk. II. Laboratory Techniques for the Preparation and Study of Sterile Evaporated Milk

Dairy Products Laboratory, Eastern Utilization Research and Development Division, USDA, Washington 25, D. C.

ABSTRACT

Laboratory techniques for the preparation and study of high temperature-short time sterilized evaporated milk are described. A bomb, falling-ball microviscometer combination, easily constructed in large numbers, is employed for containing samples during sterilization and storage, and for following changes in viscosity. Normally, the instrument constant for the microviscometer is determined by standardization against liquids of known viscosity. This procedure is too time-consuming and tedious for research on evaporated milk. For such research, studies show that the instrument constant may be calculated expeditiously, with sufficient accuracy, with the help of the following equations:

C_M is the instrument constant, d and D are, respectively, the diameter of the ball and tube,
is a function of the ratio between the diameters, and is the angle of inclination of the tube. Forewarming and evaporation are carried out in a rotating film evaporator, and sterilization in a thermostatically controlled oil-bath. An electrically operated metronome is employed for controlling the time of sterilization. Small-scale homogenization is facilitated by the employment of a diesel nozzle tester and nozzle combination modified to function as a hand-homogenizer. The application of the techniques to the study of gelation is illustrated in studies on milks containing added calcium salts and phosphates. Wide variations in [Ca^{+ +} ] and [HPO₄⁼ ] influenced storage stability to only a small degree, with a small advantage accruing to the use of limited quantities of calcium salts. False body, but not the minimum viscosity attained during storage, increased markedly with increasing [Ca^{+ +} ]. Repeatability of results was quite satisfactory. In one series of experiments based on the same sample of whole milk, a mean storage life of 84 days was observed; the limits for the mean at a 95% confidence level were ± 5 days.