This document provides information about different methods of drying grains and agricultural products. It discusses natural drying methods like solar or sun drying, as well as mechanical drying methods like heated air convective drying, freeze drying, vacuum drying, fluidized bed drying, and spray drying. For each method, it outlines the basic process, advantages, and disadvantages. The key methods covered are natural sun drying, mechanical heated air drying, contact plate drying, freeze drying, vacuum drying, and fluidized bed drying. The document aims to strengthen understanding of drying basics and acquaint students with various drying principles and technologies.

1. DISCOVER . LEARN .
EMPOWER
University Institute of
Agriculture Sciences
B.sc Agriculture Sciences
BLOCK-9
Subject Name and Code
Protected cultivation and Post harvest
management
AGT-352

2. 1
University Institute of Agriculture
sciences

3. University Institute of Agricultural
Sciences
Harvinder Singh/Dr.Ambika
Name of Topic:Types of drying
Chapter 3.2
Lecture 2
DISCOVER . LEARN .
EMPOWER

4. 4
Objectives
To strengthen the understanding of basics of protected
cultivation.
To focus on Planning and design of greenhouses
• To acquaint students with principles of green house technology
• To provide basic knowledge of planning and design of greenhouses
Course Outcome

5. INTRODUCTION
5
• Drying is the universe method of conditioning grain by removing
moisture.
• It is the oldest most common method of grain drying in
agriculture.
• It is a essential process for conditioning the grains for safe
storage.
• Correct drying method preserves the quality, nutritive value and
viability of grain.
• Drying involves both heat and mass transfer operations.
• Drying and Evaporation are the major moisture removal
methods.

6. Methods of Drying
• There are many methods to develop water-vapour pressure difference between product and
atmosphere.
• For increasing of water vapour pressure of grain, the methods are:
1. Solar or sun drying
2. Conduction drying
3. Infra-red drying
• The methods usually employed to lower the water vapour pressure of air are:
1. Heated air drying
2. Desiccated air drying
3. Refrigerated air drying
6

7. Natural Drying
• Natural drying is the method of drying, in which we are
using the natural source (viz. Sun) for drying of food
products.
• It is also known as sun/solar drying.
• Sun drying is cheaper method due to natural source of
drying. While it is slow process, very prone to contaminants
as well as weather dependent. That is why it is not most
common in commercial scale.
Types of sun drying:
Drying of standing crops, Drying of grains on stalks,Drying
of threshed grains

8. Advantages:
• Free
• No added cost for equipment
• No added cost for electricity or gas
Disadvantages:
• Contaminations from the environment.
• Product losses and contaminations by
insects and birds.
• Floor space requirements.
• Difficulty in controlling the process.
• Inconsistent sensory quality.

9. Mechanical Drying
• Mechanical drying is the method of drying of foods by means of mechanical
systems.
• Hot air is produced by the system which is used for the drying of food
material.
• Several mechanical dryers are developed by the researcher in the field of
food
technology.
• Various types of mechanical drying system available in the market which are
hot air convective drying, freeze drying, vacuum drying, fluidized bed
drying, spray drying, microwave drying, vacuum assisted microwave drying,
microwave assisted fluidized bed drying.

10. Advantages
• Quick method
• Perfect drying is possible even under unfavorable weather condition.
• Seed loss is minimized
• Small no of unskilled labors
• Required little space
Disadvantages
• Requires specialized equipment and machine, which is costly.
• Care should be taken while drying the seed using hot air, as it causes damage to the
seed.
• Tempering is to be followed while drying the seed in this method.

11. Mechanical Drying Methods
1. Contact drying
• In this methods, heat is supplied to wet products by conduction.
• Heat is transferred through a heated surface like plate, dryer wall etc.
• Thermal efficiency is higher, but product quality may be affected.
2. Hot air convective drying
• The principle of hot air convective drying is based on conventional
heat transfer from heated air to the
material being dried.
• Hot air is forced through the material and does the moisture diffusion
process that result in the drying
• This method has been widely used in industries.
• Different types of dryers have been developed and employed in
commercial production.
• Heated air is blown through the material by cross flow
or by fan generated flow.

12. 3. Freeze drying
• Freeze drying is the technique of removing the moisture content from the liquid food,
by freezing and removing the water portion of the food materials.
• Some pharmaceuticals are heat sensitive.
• Some fruits and vegetables lose their aroma and
flavor if they remain in high temperature for
significant figure of time.
• For such cases freeze-drying is an alternative.
• Freeze drying requires several successive steps, as pre-
freezing, primary drying, secondary drying, conditioning and dehydration.
• It is expensive and requires sophistication.
• Hence, it is difficult to apply to all commercial drying
needs.

13. 4. Vacuum drying
• The basic principle of vacuum drying is to remove the
water by means of vacuum.
• There are four essential elements in a vacuum drying
system: a vacuum chamber, vacuum generating device,
system for collecting water vapor and means for
supplying heat required for vaporization of water.
• For reasons similar to freeze-drying vacuum drying is
also an expensive drying method.
• It is used only for costly products.

14. 5. Fluidized bed drying
• Fluidized bed drying is the drying technique in which fluidization is take
place.
• Fluidization provide better surface area of heat and mass transfer.
• Fluidized bed dryer are found throughout all industries, from heavy
mining through food, fine chemicals and pharmaceuticals.
• They provide an effective method of drying relatively
free flowing particles with a reasonable narrow
particles size distribution.
• Fluidized bed dryers can process a wide variation of feed rates from
pounds to several hundred tons per hour.
• Two principle types of fluidized bed dryers exist- 1 static fluid bed, 2.
vibrating fluidized bed.

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