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The Freezing Point of Milk. A Review¹

Department of Dairy Industry, Cornell University, Ithaca, New York

ABSTRACT

The literature clearly shows that the freezing point of milk varies within relatively narrow limits. Some of the variations that do occur have been attributed to seasonal effects, feed, water intake, time of day (i.e., morning versus evening milk), breed of cow, and method of handling samples. In handling milk samples, it has been reported that storing them at low temperatures, or freezing them, may raise the freezing point. Some analysts claim that heat treatment affects the freezing point slightly, whereas other workers have not observed any change. Vacuum treatment of milk has been reported to raise the freezing point slightly. Some of the apparent differences in freezing points reported by different workers may be due to differences in analytical techniques. Comparison of the freezing points reported by different analysts for identical samples reveals a need for more careful standardization of the method. It is believed that more attention should be given to the calibration of the thermal sensing element. It has been suggested that salt solutions or saturated aqueous solutions of stable compounds should be used as calibration standards instead of sucrose solutions. The necessity of standardizing the manner in which the thermometer is tapped has been emphasized. The ease and speed of determining freezing points with the recently designed cryoscopes, employing thermistors as thermal sensing elements, should increase the use of cryoscopes for routine analysis. The reported results show that the freezing point of milk is a useful index for detecting added water. However, the decision to classify a sample as watered must be based upon careful consideration of all of the available evidence. One should not rely on the conclusions of others without examining their data. The published evidence indicates that the present official standard in this country should be reexamined. It has been suggested that the adoption of a minimum freezing point standard might overcome the limitations of using an assumed average as a standard.

¹ Reprints available for 90 days after publication of this paper. For prices see page 1434 of the August issue.