Most Common Adulterant in Milk

The most commonly used adulterant in milk is:

Correct Answer: Water

Water is the most commonly used adulterant in milk because it is cheap, easily available, and difficult to detect visually.

Detection of Water Adulteration

• Best method: Freezing point depression test (Cryoscopy) — addition of 1% water raises the freezing point by 0.006°C (pure milk freezing point: −0.535°C to −0.550°C).
• Lactometer reading (Specific gravity) also falls when water is added — because water has a lower density than milk.

Other Common Adulterants & Their Detection

• Urea: detected by p-dimethylamino benzaldehyde reagent
• Starch: detected by Iodine solution test (turns blue)
• Detergent: detected by Bromo-cresol-purple solution
• Gelatin: detected by Picric acid solution
• Vanaspati (hydrogenated vegetable oil): detected by Baudoin test
• Antibiotic residues: detected by Delvo kit test

Why Other Options Are Wrong

• Urea, Detergent, Starch — while these are used as adulterants, water is by far the most commonly and frequently used adulterant in milk at the commercial level.