Fish products and Byproducts Technology

Unit 3- Salting and Drying

3.2.2.a. Factors affecting the falling rate period
What are all the factors affecting the falling rate period?
Since the surface moisture of the fish has been removed, further drying of the fish depends on the movement of moisture from the interior portion of the fish to the surface.
Factors affecting falling rate period are
• Fat content of the fish
• Shape of the fish
• Temperature
• Water content
Fat content of the fish
Fish with a high fat content tend to take a longer time to dry than lean ones.
Shape of the fish
The shape and thickness of the fish influence the rate of drying of the fish. Since, diffusion is a function of thickness, thicker products require a longer time for drying.
Temperature
Diffusion will increase with rise in temperature. Drying will therefore proceed more rapidly with temperature increase.
Water content
As the water content is decreasing the rate of diffusion of water to the surface layers is also reduced.
What is case hardening in drying process?
If the drying process is above ambient temperature, the constant rate period can be very fast. Here there is every possibility that the surface of the fishes dry, whereas the interior remains moist. Here diffusion from the interior to the surface will take place very slowly. The product will be dry on the surface and transfer of moisture from the interior will not take place. This is known as case hardening and this is mainly due to the deposits of soluble proteins and other solutes on the surface.