Official Test for Milk Sterilization Efficiency

The official test for judging the efficiency of sterilization of milk is:

Correct Answer: Turbidity test

The official test for judging the efficiency of sterilization of milk is the Turbidity test.

Important Distinction — Sterilization vs. Pasteurization Tests

• Turbidity test: Used to detect adequacy of sterilization (the official test for sterilized milk).
• Phosphatase test: Used to detect inadequacy of pasteurization (NOT applicable to sterilized milk — phosphatase is already destroyed at pasteurization temperatures; sterilization goes far beyond that).

Why Phosphatase Test is Not Used for Sterilization

• Phosphatase enzyme is destroyed at pasteurization temperature (72°C/15 sec).
• Sterilization uses much higher temperatures (110–121°C), so phosphatase would already be absent — the test would be positive (no phosphatase) but cannot distinguish between pasteurized and sterilized milk.
• The Turbidity test uses the heat-coagulable whey proteins to distinguish sterilization from pasteurization.

Other Quality Tests for Reference

• COB test: Heat stability of milk
• Dye reduction test: Extent of bacterial contamination
• Coliform count: Faecal contamination