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The Effect of Heating on the Hydrogen-Ion Concentration and on the Titratable Acidity of Milk

Research Laboratories, Bureau of Dairying, United States Department of Agriculture, Washington, D. C.

ABSTRACT

Conclusions: The heating of skim milk at temperatures near the boiling point causes first a drop and then a rise in the titratable acidity of the milk. The hydrogen-ion concentration increases continuously. The initial drop in titratable acidity has been shown by previous investigators to be due to loss of carbon dioxide from the milk; the increases in titratable acidity and in hydrogen-ion concentration are due to the formation of acids from certain constituents of the milk. During coagulation, the rate of change of hydrogen-ion concentration is considerably lessened due to buffer readjustments not yet explained in detail. At the same time, there is an uneven distribution of the free acid between the whey and the curd, due probably to adsorption of the acid by the curd.

The amount of acid production is dependent on both time and temperature of heating. We do not agree entirely with previous workers as to the sources of the acid, and shall present in a future paper experimental data bearing on the nature of the chemical reactions involved.

This article has been cited by other articles:

				S. A. Kaloyereas The Effect of Pasteurization on the Stability of Phosphates Can Be Used as a Test for Heated Milk Science, July 16, 1954; 120(3107): 111 - 112. [PDF]