Factors Decreasing Specific Gravity of Milk

The specific gravity of milk is decreased by:

Correct Answer: Both addition of water and addition of fat

The specific gravity (SG) of milk is decreased by:

1. Addition of water: Water (SG = 1.000) has lower density than milk (SG ~1.028–1.032), so adding water dilutes milk and lowers its SG. This is the basis for detecting water adulteration.
2. Addition of fat/cream: Milk fat has SG of about 0.93 (less than 1), so adding cream or fat lowers the overall SG of milk.

Factors Increasing Specific Gravity

• Addition of skim milk: Skim milk (SG 1.035–1.037) has higher SG than whole milk, so adding it increases SG.
• Removal of fat/cream: Removing the lower-density fat fraction increases overall SG — that's why skim milk has higher SG than whole milk.

Recknagel Phenomenon

The specific gravity of freshly drawn milk is low — it increases by about 0.001 as time advances. This is because dissolved gases escape and fat globule distribution stabilizes after milking.

Why Other Options Are Wrong

• Addition of water only → correct but incomplete; fat also decreases SG.
• Addition of fat only → correct but incomplete; water also decreases SG.
• Addition of skim milk → this actually INCREASES specific gravity, not decreases it.