Question

For roller drying process, milk is first concentrated upto :

• A. 18 - 25 % Total solids
• B. 28 - 55 % Total solids
• C. 38 - 65 % Total solids
• D. 48 - 75 % Total solids

Hint:

Remember the pre-concentration limits: - Roller Drying = \(18\%\) to \(25\%\) Total Solids (viscosity limit for film formation).
- Spray Drying = \(45\%\) to \(52\%\) Total Solids (optimized for spray atomization).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Roller (drum) drying is a method of drying milk by applying a thin layer of liquid onto the surface of rotating, steam-heated metal drums.
Before drying, milk is pre-concentrated in an evaporator to improve drying efficiency, but the maximum concentration is limited by the viscosity requirements of the process.

Step 2: Detailed Explanation:
Let us compare the concentration limits for roller drying and spray drying:
For spray drying, milk is concentrated to a high solids level (\(45\%\) to \(50\%\) total solids) because high-pressure nozzles or rotary atomizers can easily disperse concentrated feeds.
However, for roller drying, milk can only be pre-concentrated to \(18\%\) to \(25\%\) total solids.
If the milk is concentrated beyond \(25\%\) total solids:
- The viscosity of the milk increases significantly.
- It becomes difficult to distribute the milk uniformly across the rotating drum surface.
- The resulting milk film on the drum becomes too thick and uneven.
- A thick film leads to incomplete drying, heat damage (caramelization of lactose), and scorching.
Therefore, maintaining a lower total solids level of \(18-25\%\) is essential to ensure a thin, uniform film and a high-quality product.

Step 3: Final Answer:
For the roller drying process, milk is first concentrated to 18 - 25% Total solids.