Question

The specific gravity of milk is lowered by the addition of -

• A. Skim milk
• B. Water and cream
• C. Sugar
• D. Salt

Hint:

Remember this simple rule for lactometer readings (which measure specific gravity): Adding water lowers the reading. Removing fat (making skim milk) increases the reading. Adding both water and removing fat can be done to try and normalize the reading, which is a sophisticated form of adulteration.

Answer 1

The Correct Option is B

Step 1: Specific Gravity Explained:
Specific gravity (SG) is the ratio of a substance's density to that of a reference (usually water). Milk's SG is determined by its composition. Adding substances with lower SG decreases the overall SG; higher SG additives increase it.
Step 2: Key Data:
Compare the specific gravity of potential additives to that of normal milk.
Whole milk SG (average): \(\approx\) 1.028 - 1.032
Water SG: 1.000
Milk fat (cream) SG: \(\approx\) 0.93 (less dense than water)
Solids-Not-Fat (SNF) SG: \(\approx\) 1.6
Skim milk SG (high SNF, low fat): \(\approx\) 1.036 (higher than whole milk)
Step 3: Impact of Additions:
Analyze each addition's effect:
(A) Skim milk: SG \(\approx\)1.036, higher than whole milk; it increases SG.
(B) Water and cream: Water (SG 1.000) and cream (SG \(\approx\)0.93) are significantly lower than milk's SG. Adding either decreases the mixture's SG, a common adulteration method.
(C) Sugar: Increases solids concentration, raising density and SG.
(D) Salt: Like sugar, increases dissolved solids, thus increasing SG.
Step 4: Conclusion:
Water and cream lower milk's specific gravity.