2. Vaporization of moisture from the surface of
the material
Movement of moisture from the interior of
the food to its surface as a result of diffusion,
cell contraction and vapour pressure gradient
2
3. Convenient storage and packaging
Easy transportation
Long shelf life
Desired textural changes
Improved final product
3
5. Fig : Typical drying rate curves: (a) drying rate versus drying time,
(b) drying rate versus water content.
5
6. ADVANTAGES DISADVANTAGES
Long shelf life Loss of micro nutrients
Reduced weight Loss of colour
Concentration of nutrients increases Changes in flavour and texture.
No refrigeration is required for dried
products.
Some drying methods are expensive
6
7. Contact drying or convective drying: Material is in
direct contact with the drying air and moisture
from the material directly evaporates to the
surrounding air
Vacuum Drying: Material is dried under vacuum
at much lower temperatures compared to contact
drying. Heat is added indirectly either by
conduction or radiation.
Freeze Drying: in this method water is removed
by process of sublimation. Suitable temperature
and pressure conditions are maintained to ensure
sublimation.
7
9. Traditional Sun drying
Solar dryer
Mechanical Hot Air dryer
Vacuum drying
Microwave Based / Radiation drying
Osmotic drying
Freeze drying
Super heated steam drying
Drum drying
Fluidized Bed drying
Foam Mat drying
9
10. The material is sprayed in thin layer on
ground. It depend upon…
- Temperature, Humidity, Wind-velocity, &
Time
Disadvantages
- Microbiological Contamination
- Dust & Soil Contamination
- Insect Contamination
- Foreign Matters
- Unhygienic Condition
- Non uniform drying
10
11. •It offers as an alternative process.
•Provide food item in clean, hygienic and sanitary
conditions.
•Advantages
• Zero energy cost
• Saves time, energy & area.
• Protect the environment.
11
12. • Principle: The food materials in the trays are dried
by direct contact with hot air
• Disadvantages
• Takes Long Time to dry.
• Low energy efficiency.
• Causes Quality Deterioration
• .
12
13. ●Removal of moisture under low pressure.
●Vacuum pressure (50-100 mbar) is usually applied
●The reduction in the pressure causes the expansion of
water molecules in the vapor phase & escape of vapor
occluded into Pores.
13
14. Considered as Fourth Generation drying technology.
Based a unique volumetric heating mode facilitated
by electromagnetic radiation at 915 or 2,450 MHz.
Advantages
Shorter drying time. Improved product quality.
High energy efficiency & Flexible Case hardening can
be reduced.
Limitations
Expensive
Limited applications to date.
14
15. Osmotic dehydration has the potential to remove water at low
temperatures;
An energy efficient method, as water does not go through a
phase change
Osmotic dehydration is generally used as a preliminary step for
further processing such as freezing (Ponting et al., 1966), freeze
drying (Hawkes and Flink, 1978), vacuum drying (Dixon and Jen,
1977), microwave heating and processing applications (Nelson
and Datta, 2001), and air drying (Mandala et al., 2005).
Commercial significance as a complementary processing step
◦ reduced discoloration of the fruit,
◦ reduced heat damage to texture
◦ increased retention of volatiles
◦ increased sugar to acid ratio which improves the textural quality
◦ low operating costs
15
16. •Provides best quality of product in general.
•Good for heat sensitive materials.
• Moisture is removed from the solid state (ice)
directly to the vapor state by sublimation.
• Drying actually occurs in two steps, primary and
secondary drying stages.
• It is in the primary stage that water is removed by
sublimation,
• Whereas vaporization of unfrozen liquid water
molecules occurs in the secondary stage of drying.
16
18. • Atomization produces droplets with very large
surface area for drying.
– High pressure nozzle:
– Centrifugal atomizer
• Air Handling - Ambient air is taken in through a
vent and heated
• Heating – Electric, diesel, steam.
• Inlet air at 150-300°C outlet air temperature of 90-
100°C, which corresponds to a wet-bulb temperature (and
product temperature) of 40-50°C
Dryer Chamber - In the residence time of droplets to
bring moisture 40% to only about 5-8%.
• The food droplets are sprayed - fall down to the bottom by
gravity..
18
20. • Emergent technology with great potential.
• Work with efficient drying medium (Superheated Steam).
• Higher Drying Rates (Both constant & Falling rate period).
• Drying takes place through direct contact between superheated steam &
the product to be dried.
Advantages
Net energy consumption can be minimized (if exhaust can be used).
Oxidation or Combustion can be avoided.
Eliminates the risk of fire & explosion hazards.
Allows Pasteurization, Sterilization .
Energy saving & emission reduction.
20
22. In this system the product pieces
are suspended in the heated air
throughout the time required for
drying
The movement of product
through the system is enhanced
by the change in mass of
individual particles as moisture
is evaporated.
The movement of product
created by fluidized particles
results in equal drying from all
product surfaces.
22
23. Foaming of liquid and semi-liquid
materials to shorten drying time.
To obtain products of desired
properties (e.g., favourable
rehydration, controlled density),
To retain volatiles that otherwise
would be lost during
The drying of non-foamed
materials.
Soy protein isolates, egg white,
methyl cellulose.
thin layer (0.1 to 0.5mm) at 65
and 85°C, short duration
It is reported to be considerably
cheaper than vacuum, freeze and
spray drying methods.
Good quality tomato powder can
be produced using this technique
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