Most Constant Physical Property of Milk

The most constant physical property of milk is:

Correct Answer: Freezing point

The freezing point is the most constant (stable) physical property of milk. It remains nearly unchanged regardless of breed, season, or feed, making it the best indicator of water adulteration.

Freezing Point of Milk

• Cow or Buffalo milk: −0.535°C to −0.550°C (average: −0.545°C)
• Average depression of cow milk: −0.547°C; buffalo milk: −0.549°C
• Lactose and chloride are primarily responsible for depressing the freezing point.
• Addition of 1% water raises freezing point by 0.006°C.
• Measured by: Hortvet cryoscope

Why Freezing Point is Used to Detect Water Adulteration

Since it is so constant, even a small addition of water (which has a freezing point of 0°C) raises the freezing point measurably, making it the best test for detecting water adulteration.