Agriculture ppt Savitra and alka

1. • Preserving fruits, vegetables, grains, and meat has
been practiced in many parts of the world for
thousands of years.
• Methods of preservation include: canning, freezing,
pickling, curing (smoking or salting), and drying.
• Food spoilage is caused by the action of olds, yeasts,
bacteria, and enzymes.
• The drying process removes enough moisture from
food to greatly decrease these destructive effects.
Drying

2. Necessity of drying
There is an essential need to dry grain,
fruits and vegetables quickly and effectively
after harvest and before storage to retain
maximum quality, to attain a moisture content
sufficiently low to minimise infestation by
insects and microorganisms (bacteria, fungi,
etc.), and to prevent germination

3. Moisture content
• It is the amount or quantity of moisture (water)
present in the product.
• Water content can be directly measured using a
known volume of the material, and a drying oven.
Volumetric water content, θ, is calculated using:
• m wet – m dry
• θ = --------------------
ρw X Vb
• where
• mwet and mdry are the masses of the sample before
and after drying in the oven; ρw is the density of
water; and Vb is the volume of the sample before
drying the sample.

4. • It is expressed in terms of wet basis or dry
basis
• The moisture content on wet basis means the
mass of water per unit mass of the moist
specimen
• Whereas the moisture content on dry basis
means the mass of water per unit mass of the
sample's dry weight

5. • The moisture content of fresh foods ranges
from 20% to 90%.
• The moisture content of rice must be reduced
from 24% to 14% of the total weight.
Therefore, drying 1,000 kg of rice requires the
removal of 100 kg of water.
• Safe storage generally requires reducing the
moisture content to below 20% for fruits, 10%
for vegetables, and 10-15% for grains.
• If food is properly dried, no moisture will be
visible when it is cut.

6. Process of Drying
• In the process of drying, heat is necessary to
evaporate moisture from the product and a flow of
air is needed to carry away the evaporated moisture.
• There are two basic mechanisms involved in the
drying process; the migration of moisture from the
interior of product to the surface, and the
evaporation of moisture from the surface to the
surrounding air.
• The rate of drying is determined by the moisture
content and the temperature of the grain and the
temperature, the (relative) humidity and the velocity
of the air in contact with the grain.

7. Open Sun-Drying
• The common approach to drying fruits,
vegetables and grains in many tropical
countries is to spread them on mats or cloth
just on the front porch.
• This can be seen in many places in India.
• In cities, they dry on the terrace floor...what is
more, often times the grains are spread on the
asphalt roads or sand to dry.
• One can see chillies and grains dried this way.
This is sun-drying.

9. Disadvantages of Open Sun-Drying
• It takes more drying time as the temperature
of air is ambient.
• The product may be accumulated with dust
during drying process.
• It may be attacked by domestic animals.
• The dried product is often of poor quality as a
result of grit and dirt.
• The product is often unhygienic as a result of
microorganisms and insects such as flies.
• Finally it may result in fetching of lower price
to the dried product.

10. Solar Dryer
It is a device which uses solar energy for drying of
products.
Solar Drier Components
• A solar collector that heats the air
• A drying chamber in which product is dried and
• Some type of airflow system

11. Drying
Chamber
Airflow
Solar
Collector

12. Drying Methods
• Direct type or natural circulation/convection drying
• In-Direct type or Forced circulation/convection drying
Based on methods there are essentially two types of
dryers:
1 Box/cabinet type -direct
2 Box type-indirect

13. • In direct type Box, it is having single box
which carries an absorber [say, a black metal
sheet or black paper] and a tray for keeping
products, with preferably holes in it or a net or
matting----kept above the absorber.
• The sunlight falls directly on the products
through the transparent cover.
Direct type dryer

14. Examples of Direct Type Driers
Cabinet type dryer

15. Examples of Direct Type Driers
Mini Multi Rack type dryer

16. Examples of Direct Type Driers
High Capacity Multi Rack type dryer

17. Mini Multi Rack type dryer loaded with fig and grapes

18. High Capacity Multi Rack type dryer loaded with fig

19. • In the indirect type box, it has two boxes---one collector box with window
and absorber as given above and another box called drying chamber with
racks to keep the products.
• An auxiliary unit like blower and heaters are used.
• The drying box is kept at a higher level to provide natural convection or
forced convection .
• The two boxes are connected by an insulated duct or pipe.
• Note that for large boxes, the absorber box can be kept outside and the
dryer box inside a building, the duct taken through a window or opening in
the wall.
• You can add a chimney to the box---- to provide a faster flow of hot air.
• Passive dryers are without a fan or blower...just the natural convection to
push the air out.
• Active dryers have an exhaust fan or blower to aid flow of air.
• A major advantage is that the absorber box can be a large with more area
exposed to sunlight and we can control the temperature of the product.
Indirect type dryer

20. Examples of In-Direct Type Driers
Forced circulation type drying system

21. Solar Tunnel Drying
• For large scale drying, a tunnel type of dryer
is used....the products items are kept in trays
and passed through a tunnel which is covered
with glass or plastic sheeting.

22. Line diagram of solar tunnel dryer

26. Discussion with president of Karnataka
grape growers’ association about grapes
drying at the user’s site
A view of existing system of
grapes drying in and around
Bijapur district

28. Pretreatment:
Fresh fruits
Washed in fresh water
Fumigation for 3 hours with
Sulphur fumes (3 g / kg)
Dipping for 3 minutes in the solution of
1.5 l of Keno oil + 2.5 kg of Potassium carbonate
in 100 l of water for 1000 kg of grapes
Drying
The above solution sprayed during drying
alternate days upto 7th day
Storage
The project is under progress.