Question

In the falling rate drying period, the moisture content of the food product:

• A. Decreases rapidly
• B. Remains constant
• C. Decreases at a decreasing rate
• D. Decreases at an increasing rate

Hint:

Most food materials are hygroscopic and capillary-porous, meaning they dry almost entirely in the falling rate drying period.
The rate of drying in this period is limited by interl moisture diffusion rather than surface evaporation.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Drying of food materials typically occurs in two main stages: the constant rate period and the falling rate period.
The transition between these two stages is called the critical moisture content.

Step 2: Detailed Explation:
During the constant rate period, the food surface is completely wet with free water.
The rate of evaporation depends solely on exterl conditions (air temperature, humidity, and velocity).
Once the critical moisture content is reached, free water is no longer available at the surface.
The drying rate is then governed by interl mass transfer resistance (diffusion of water from the interior to the surface).
As drying progresses, the moisture pathway becomes longer and more tortuous, leading to a continuous reduction in the drying rate.
Consequently, the moisture content of the product decreases, but the speed of this decrease slows down over time.
Thus, the moisture content decreases at a decreasing rate until it approaches the equilibrium moisture content.

Step 3: Fil Answer:
The correct option is (C).