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The Relation of Acidity to the Coagulation Temperature of Evaporated Milk

Research Laboratories of the Dairy Division, United States Department of Agriculture

ABSTRACT

The variation in the coagulation temperature of mixed herd milk is comparatively small and has little relation to the coagulating temperature of the same milk after evaporation. Consequently the temperature at which evaporated milk made from the mixed milk of a number of cows will curdle cannot be predicted with any accuracy by determining the coagulating temperature of the raw milk.

The interrelation of the constituents of the ash of the milk, which has been shown to be a factor in determining the coagulating point of fresh milk from individual cows, is only a minor factor in determining the coagulating temperature of evaporated milk. This is partly due to the rearrangement of the acid-base relation in the condensing process, and partly to the obscuring effect of other factors, which in the mixed milk from many cows become of much greater significance.

The effect of high forewarming in raising the coagulating temperature of evaporated milk is evidently due to the precipitation of part of the calcium. Forewarming temperatures much below 95°C. (203°F.) have little effect on the coagulating temperature.

The effect of high forewarming may be increased by prolonging the heating.

There is no very definite relation between the coagulating temperature of evaporated milk and the true acidity, as measured by determining the hydrogen-ion concentration of the milk before sterilization. There is a comparatively wide limit within which the hydrogen-ion concentration may vary without influencing the coagulating temperature.

A very small increase in the acidity from the normal for that particular milk will cause a distinct lowering of the coagulating temperature of the evaporated milk.

Other factors which have not yet been fully investigated have an important influence on the coagulating temperature without appreciably changing the acidity.