The document discusses drying and dehydration processes, detailing their definitions, differences, and importance in food engineering. It covers various drying methods, including natural and artificial techniques, and explains different types of dryers used in agriculture. The information emphasizes the significance of effective drying for quality preservation and microbial spoilage reduction.

1. DRYING AND
DEHYDRATION
Presented by
Shaswat Tiwari
Ph.D. ( PHP & FE)
Submitted to
Dr. Mohan Singh
Professor and Head
Department of Post Harvest Process and Food
Engineering
College of Agricultural Engineering
Jawahar Lal Nehru Krishi Vishwavidyalaya
Jabalpur MP

2. Contents
 Introduction
 Moisture Migration During Drying
Process
 Drying Rate Curve
 Difference Between Drying and
Dehydration
 Importance of Drying Process
 Drying Methods
 Mechanical Dryer Methods
 Types of Dryer

3. Introduction
o Drying refers to the removal of
small amount of moisture from a
solid or semi solid material by the
evaporation (change of phase from
liquid to vapors /gas).
o Dehydration means removal of
moisture to a very low level usually
up to bone dry condition.
o It involves both heat and mass
transfer operations together.

4. Moisture Migration During Drying Process

5. Drying Rate
Curve

6. Drying
• It is natural process
• It does not have control over
any climatic condition.
• It takes more time.
• Do not have good quality.
Dehydration
• It is an artificial process
• It has control over climatic
condition.
• It takes less time
• Dehydrated food have good
quality.

7. Importance of Drying Process
Minimize Microbial
Spoilage
Continuous Supply of
Commodity
Early Harvest
Better Quality
Available During off
Season
Improved Milling
Food Product Development

8. Drying Methods
The agricultural product drying
methods can be broadly grouped into
two-
oSun/Solar drying
oArtificial drying with mechanical
means

9. Mechanical
Drying Methods
Contact Drying
Convective Drying
Freeze drying
Radiation Drying
Super heated steam drying
Fluidized Bed Drying

10. Contact Drying
• In this method of drying heat is
supplied to wet products by
conduction.
• The commonly used heating medium
in conduction drying are steam,
organic liquids, metals and other
materials with high value of heat
transfer coefficient.

11. Convective
Drying
• In this method sensible heat
of heated air is transferred
to the wet products by
convection.
• Heated gaseous medium
usually air is used.

12. Freeze Drying
This method is based on
the sublimation of frozen
moisture from the wet
product in a drying
chamber.
Heat is supplied by
radiation or conduction
from heated trays and the
temperature of product is
not raised to above 0°c

13. Radiation Drying
• Heat energy is supplied through
the electromagnetic waves. The
wavelength of the electromagnetic
radiation lies between 0.76 to 400
micron.
• The moisture migration inside the
materials and diffusion of vapor
follow the same laws as in
convection or contact drying

14. Super Heated steam drying
• Superheated steam drying (SSD)
uses steam heated beyond its boiling
point to remove moisture from
materials. This creates a unique drying
environment with several advantages
over traditional hot air drying.
• Advantage
• Faster drying
• Higher quality
• Energy efficiency
• Sanitization

16. Fluidized Bed drying
In this method of
drying products are
being dried under
fluidized condition in a
dryer.
The materials are
fluidized by drying
air with sufficiently
high velocity to
cause suspension.

18. Types of
dryer-
Deep bed Dryer
Flat bed Dryer
Recirculating Dryer
LSU Dryer
Rotary Dryer
Tray Dryer
Tunnel Dryer
Spray Dryer
Vacuum Dryer

19. Deep Bed
Dryers
• A deep bed dryer is a type
of industrial dryer that's
used to remove moisture
from large volumes of
material.
• The most common shapes
are round or rectangular.

20. Flat bed dryer
• The Flat Bed batch type
dryer is similar to deep bed
dryer except that the surface
area of the dryer is more
and the depth of the drying
layer is less.
• These dryers are usually of
1-2 tones capacity.

21. Recirculating Dryer
• In a re-circulating dryer the same quantity
of grain is recycled through the dryer until
final moisture content is reached.
• Recirculatory batch dryer is a continuous
flow non mixing type of grain dryer.

22. LSU Dryer
• Developed at Louisiana
state university (LSU)
• Continuous mixing type
dryer
• Developed specifically for
rice to ensure gentle
treatment, good mixing &
good air to grain contact

23. Rotary Dryer
• The foodstuff is contained in a horizontal
inclined cylinder through which it travels,
being heated either by air flow through
the cylinder, or by conduction of heat
from the cylinder walls.
• In some cases, the cylinder rotates and in
others the cylinder is stationary and a
paddle or screw rotates within the
cylinder conveying the material through.

24. Tray Dryer
• Also known as cabinet dryer.
• It is a rectangular chamber made
up of steel which is insulated.
• Trays are placed one above the
other and products are spread on
the tray uniformly to a height of
0.1-1 cm.
• It consists of a fan, a heater and
thermostatic control to heat air to
desired temperature

25. Tunnel Dryer
• Tunnel dryers consist of long tunnels
through which trucks carrying stacks of
trays travel with or against a stream of
drying air.
• The material to be dried is evenly spread
on the trays.

26. Spray Dryer
• Spray drying is a method of
producing a dry powder from a liquid
or slurry by rapidly drying with a hot
gas.
• Spray Dryer is widely used industrial
process for transforming liquid feeds
into dried particles

27. Vacuum Dryer
• A Vacuum Dryer is used
dry the materials by the
application of vacuum.
• Hence, water evaporates
faster. The heat transfer
becomes efficient for
example; the rate of drying
enhances substantially

28. Thank You