Question

Which of the following type of powder does not possess occluded air ?

• A. Spray dried
• B. Instantized
• C. Roller dried
• D. Fluid bed dried

Hint:

Because roller-dried milk powder lacks occluded air, its particles are flat, solid flakes.
This high density makes it sink quickly when reconstituted, though it has poorer overall solubility due to the high thermal stress of the drum surface.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Occluded air refers to the air bubbles trapped inside the individual powder particles during the drying process.
The presence or absence of occluded air depends on the physical drying mechanism used.
Detailed Explanation:
Let us compare the drying mechanisms of the different processes:
- Spray Drying (A) and Instantizing (B): In these methods, liquid milk is atomized into fine droplets inside a drying chamber.
As these droplets contact hot air, moisture evaporates rapidly from their surfaces, trapping air bubbles inside the forming crust of each particle.
This results in high levels of occluded air.
- Fluid Bed Drying (D): This is typically used as a second-stage drying step for spray-dried powders, meaning the powder already contains occluded air from the initial atomization step.
- Roller Drying (C): In this process, a thin film of milk is applied directly to the outer surface of steam-heated, rotating metal drums.
Moisture evaporates directly from the flat liquid film, which is then scraped off as a continuous sheet by a knife blade and ground into powder.
Since no droplets are atomized in an air stream, there is no mechanism for air to become trapped inside the particles.
Therefore, roller-dried milk powder contains virtually no occluded air.

Step 2: Final Answer:
Roller dried powder does not possess occluded air.