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Changes in pH of Milk During Freezing and Frozen Storage¹

Division of Applied Biology, National Research Council, Ottawa, Canada

ABSTRACT

Measurement of pH during freezing and frozen storage of pasteurized and raw milk and of raw milk with added calcium, phosphate, and citrate showed that marked pH changes occurred in frozen milk. During slow freezing, the pH of milk decreased to values as low as 5.8, whereas little change in pH occurred during fast freezing. During storage at –7° C. as well as at –12° C. the pH decreased to a minimum during the first 2 to 3 wk. of storage, and increased gradually thereafter. The pH minimum of pasteurized milk and raw milk with added salt (5.8–6.0) was generally lower than that of raw milk (6.1–6.2). The increase in pH after the pH minimum was reached was more gradual in pasteurized milk and raw milk with added chemicals than in raw milk. Although the amount of precipitated protein was measured simultaneously with pH, the data did not indicate a definite relation between pH changes and protein precipitation.

¹ Contribution from the National Research Council, Ottawa, Canada. Issued as N.R.C. No. 6055.