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Conductivity, Per Cent Lactose, and Freezing Point of Milk

Department of Dairy Science, A & M College of Texas, College Station

ABSTRACT

Milk from individual cows and from groups of cows was examined for its freezing point and for factors affecting the freezing point.

Based on results obtained with 100 raw milk samples from individual cows, lactose was found to be the most important factor governing the freezing point of milk. Of the 62 samples with over 4.5% lactose, 23 (37%) had freezing points of –0.550° C. and below, and 6 (10%) had freezing points above the 3% water-tolerance level, namely, –0.5335° C.

Of the 38 samples with 4.5% lactose or less, none had a freezing point of –0.550° C. or below, but 22 (58%) had freezing points of above –0.5335° C.

The specific conductivity of milk varied inversely with the per cent lactose. Although in low-lactose mastitic milk a legal freezing point was observed, nonmastitic milk equally low in lactose showed freezing points above the legal minimum. Both prolonged storage of raw milk and pasteurization decreased the specific conductivity of milk and raised its freezing point.