Milk Composition, Quality and Adulteration Testing
Domain 3 tests composition, legal quality standards, platform tests and simple adulteration detection. You should know what each test detects and its limitation.
Core rules
- Cow milk: fat at least 3.5% and SNF at least 8.5%; buffalo milk: fat at least 6.0% and SNF at least 9.0% under Indian legal standards.
- Gerber method measures fat; lactometer estimates specific gravity; clot-on-boiling and alcohol tests screen heat stability; acidity titration indicates souring. Platform tests are rapid screens, not full confirmations.
- Adulterants: starch gives blue-black with iodine; cane sugar is detected by resorcinol; urea by urease/color tests; detergent by foaming/chemical tests; added water by low lactometer reading and freezing-point depression.
Worked example
A sample has Gerber fat 4.0% and corrected lactometer reading 30. Using SNF = 0.25L + 0.2F + 0.76: SNF = 7.5 + 0.8 + 0.76 = 9.06%. This is acceptable for cow milk. The reasoning is that lactometer reading and fat together estimate SNF; the reading must be corrected to 20°C first.
Traps
- Using an uncorrected lactometer reading changes the SNF result.
- A lactometer alone cannot prove added water; freezing point is the reference method.
- Acidity is expressed as % lactic acid, not as °SH, unless the question asks for it.
- Do not test an unmixed sample; fat rises to the top.