Question

Heat stability of concentrated milk is measured at

• A. 140°C
• B. 120°C
• C. 160°C
• D. 180°C

Hint:

Remember these standard heat stability testing temperatures:
- Normal fluid milk \(\rightarrow\) Tested at 140°C.
- Concentrated milk (Evaporated milk) \(\rightarrow\) Tested at 120°C (due to its higher sensitivity to heat-induced gelation).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Heat stability is defined as the ability of milk to withstand high processing temperatures without coagulating or gellying.
It is measured by the Heat Coagulation Time (HCT), which is the time required for milk to show visual signs of coagulation when heated at a constant, high temperature.

Step 2: Detailed Explanation:
The heat stability of milk products varies significantly with concentration:
-Unconcentrated (Normal) Milk:
Normal fluid milk has relatively low protein and mineral concentrations, giving it high thermal stability.
Its heat stability is standardly measured at a high temperature of \(140^\circ\text{C}\).
-Concentrated Milk:
Concentrated milk (such as evaporated milk, typically containing about 20% to 22% solids-not-fat) is much more sensitive to heat.
This lower stability is caused by the increased concentration of proteins and minerals (such as calcium and phosphate), which reduces the distance between casein micelles and promotes aggregation.
Additionally, the pH of concentrated milk is lower than that of normal milk.
Due to this lower stability, heating concentrated milk at 140°C would cause almost instant coagulation, making it impossible to measure differences in stability.
Therefore, the heat stability of concentrated milk is measured at a lower standard temperature of \(120^\circ\text{C}\).

Step 3: Final Answer:
The heat stability of concentrated milk is standardly measured at 120°C, which corresponds to Option (B).