Dry and dehydration process of food products. method, types, mechanism. spry dryer process. some dried food products and many others information

1. Topic: Dry and Dehydration of Food
Products.
Edit by
Mashiqur Rahman Sohag

2. Definition
Drying is a mass transfer process consisting of the removal of water
or another solvent by evaporation from a solid, semi-solid or liquid.
Method of Drying
 Thermal drying : Drying commonly describes the process of thermally removing
volatile substances (moisture) to yield a solid product.
 Non-thermal drying:
1. As Squeezing wetted sponge
2.Adsorption by desiccant (desiccation)
3. Extraction.

3. Purpose of Drying
In food technology, drying is carried out for one or more
of the following reasons:
1. To avoid or eliminate moisture which may lead to corrosion and
decrease the
product stability.
2. To improve or keep the good properties of a material, e.g. flow ability,
compressibility.
3. To reduce the cost of transportation of large volume materials ( liquids)
4. To make the material easy or more suitable for handling.
5. Preservative.

4. Types of drying
 Direct: Drying is established through direct contact
between the product and the gas heating medium.
Material reaches steady state temperature near gas wet
temperature.
 Indirect Drying: Established from heated surface in
contact with the product. The heating medium and
product are separated by wall. Material reaches steady
state temperature near liquid boiling point for contact
rate drying.
 Radiation: Heat transfer establishes by radiation from
energy source. This is no contact from heated surface or
medium and product.

5. Mechanism of Drying
Liquid diffusion: if the wet solid is at a temperature
below the boiling point of the liquid
Vapor diffusion: if the liquid vaporizes within material
Condensation diffusion : if drying takes place at very
low temperatures and pressures, e.g., in freeze drying
Surface diffusion (possible although not proven)
Hydrostatic pressure differences: when internal
vaporization rates exceed the rate of vapor transport
through the solid to the surroundings
Combinations of the above mechanisms

6. Advantage & Disadvantage of drying
 Advantage:
 Low cost.
 No refrigeration required.
 Transportation, handling & storage costs are reduces.
 Disadvantage:
 Long time required.
 Large space require & difficult to control insect or microbial.
 Not controllable & production is dependent on natural
phenomenon.

7. Some Dried Products

8. Dehydration
Definition:
Dehydration is defined as “ the application of heat under controlled conditions
to remove water from food materials”
Purposes of Dehydration:
The main purpose of dehydration is to extend shelf-life.
 To inhibits microbial growth or enzyme activity.
 To avoid or eliminate moisture.
 To improve or keep good properties of materials.
 To reduce the cost of transportation of large volume of materials.
 To make the materials easy or more suitable for handling.

9. Dehydration Equipment's
 Convective Dryers
 Contact Dryers
 Vacuum Dryers
 Freeze Dryers
 Spray Dryers

10. Factors affecting dehydration
o Surface area
o Temperature
o Time
o Air Velocity
o Humidity
o Atmospheric Pressure

12. Changes During Dehydration
 Cell / tissue Shrinkage
 Case Hardening
 Chemical Changes

13. Advantage
 Dehydrating food is a quick and easy way to preserve food.
 Dehydration prolongs the shelf life of food by reducing its moisture content
 Dehydration makes it easier and cheaper to transport some food items
 Dried food doesn't take up much room and is very light weight

14. Disadvantages
 Change or decrease color and taste due to chemical changes.
 Equipment is very expensive
 Loss of volatile components
 Color loss or changes in dehydrated food.
 dried fruits, vegetables, and meats can be exceptionally hard.