Question

Which size of the fat globules doesn't mix to the top of the milk during stored condition?

• A. Less than 2 $\mu$
• B. Less than 5 $\mu$
• C. Less than 10 $\mu$
• D. Less than 20 $\mu$

Hint:

Smaller fat globules stay suspended—this is why homogenized milk does not form a cream layer.

Answer 1

The Correct Option is A

Concept: Cream separation in milk occurs due to the rising of fat globules to the surface. This process depends on the size of fat globules—larger globules rise faster, while smaller ones remain suspended.

Step 1: Principle of Creaming.
The movement of fat globules in milk follows Stokes' Law: \[ v \propto r^2 \] where \(v\) is velocity of rising and \(r\) is radius of fat globule.

Step 2: Interpretation of Law.

• Larger globules → Rise faster → Form cream layer
• Smaller globules → Rise very slowly → Remain dispersed

Step 3: Homogenization Insight.
In homogenized milk:
• Fat globules are reduced to very small size (<2 μm)
• This prevents creaming

Step 4: Evaluating Options.

• Less than 2 μ → Too small to rise → Correct
• Less than 5 μ → Some may still rise slowly
• Less than 10 μ → Many will rise
• Less than 20 μ → Clearly large enough to rise

Step 5: Conclusion.
Thus, fat globules smaller than 2 μm do not rise to the top during storage.