Conductivity, Per Cent Lactose, and Freezing Point of Milk

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 (1_0%) 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 mastitie milk a legal freezing point was observed, nonmastitie 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.Jackson and Rothera (7) have shown that lactose and the ionizable salts exert the greatest influence upon the osmotic pressure of milk, as measured by its freezing-point depression.They found that electric conductivity and per cent lactose showed a strict reciprocity, provided that the secretion of milk samples corresponded to the same period.