Drying grains is important to allow for safe long-term storage by reducing moisture content to prevent spoilage. There are various drying methods like sun drying, convection drying using hot air or gases, and radiation drying using electromagnetic waves. Common dryers include flat bed dryers, mechanical tray dryers, and solar dryers which utilize the sun's energy. Proper drying is necessary to retain nutrients while sufficiently lowering moisture for storage.

1. Drying process for grains
Submitted by:
Pinki Chowhan
3rd Year (5th Semester)
Regd. No.
213430103420003
Roll No. 34303421027
Subject Details:
Food Process Technology-I
Code: PC-FT501
Food Technology Department
Hemnalini Memorial College of Engineering
(Affilated by MAKAUT)

2. Content
• Introduction
• Importance of drying
• Moisture content
• Types of drying methods
• Different dryers
• Flat bed dryer
• Mechanical tray dryer
• Solar dryer
• Conclusion

3. Introduction
• Dehydration is termed as removal of moisture from grain
to very low levels usually to bone dry condition.
• Drying refers to removal of moisture from grains and other
products to a predetermined level which provides a safe
level to store the grain for longer time period.
• The predetermine level of moisture removal retains the
nutritional quality of food material otherwise over drying
may deteriorate the nutritional composition of food
material.
• Drying is one of the oldest methods of food preservation.
• Drying is a thermo-physical and physio-chemical operation
by which excess moisture from a product is removed.
• Drying makes the food grains and other products suitable
for safe storage and protects them against attack of insects,
mold and other micro-organisms during storage.

4. Importance of drying process
• It minimizes microbial spoilage and chemical deteriorative
reactions greatly which provides safe storage facility for
long time.
• It Permits continuous supply of product thro’out the year
• Permits early harvest which reduces field damage and
shattering loss
• Permits the farmers to have better quality product
• Makes products available during off season
• The reduced weight of dried products decreases packaging,
handling and transportation costs.
• Most food products are dried for improved milling or
mixing characteristics in further processing.
• It helps in preparing different food product development.

5. Moisture content
• The water content of agricultural product is
given in terms of moisture content.
• It is the percentage of water content present in
product. It is designated by two methods
1. wet basis
2. dry basis

6. Drying methods
• Sun drying
• Conduction drying
• Convection drying
• Radiation drying
• Freeze drying
• Osmotic drying
• Fluidized bed drying
• Dielectric drying
• Thin layer drying
• Deep bed drying

7. Sun drying:
• Traditional method of drying.
• Drying takes place through radiation mode of sun’s
electromagnetic waves.

8. Conduction or contact drying:
• Heat is transferred to wet material mainly by conduction mode
through solid surface.
• Surface temperatures may vary widely.
• Dryers can be operated under low pressure and in inert atmosphere.
• Dust and dusty material can be removed easily.
Convection drying:
• Drying agent is hot gas or hot air and supplies heat to the wet grain.
• Steam heated air, direct flue gases of agricultural waste etc. can be
used as drying agents.
• Drying temperature varies widely.
• If atmospheric humidity is high, natural air drying needs
dehumidification.
• Fuel consumption is high as compare to conduction drying for same
capacity.
• Ex: fluidized bed dryer, hot air oven dryer

9. Radiation drying:
• Based on absorption of radiant energy of sun and
transformation into heat energy by grain.
• Moisture movement and evaporation is caused by temperature
difference and partial pressure of water vapor b/w surrounding
air.
• Ex: sun drying
Freeze drying:
• Drying is based on the sublimation (solid to gas) of frozen
moisture from wet product placed in a drying chamber.
• Works at low pressure.
• Heat is supplied by radiation or conduction mode.
Osmotic drying:
• Moisture is removed using osmo-active substance like, 60%
aqueous solution of saccharose or 25% aqueous NaCl.
• Concentration difference generated on both sides of the semi
permeable membrane.

10. Fluidized bed drying:
• Products are being dried under fluidized condition.
• Fluidization occurs by drying air with sufficient high velocity
to cause suspension.
• High rate of moisture migration takes place.
• Uniform drying.
• Used for high initial moisture content and lighter material.
Dielectric drying:
• Heat is generated within the solid by placing it in fixed high
frequency current.
• Polar molecules of substance get polarized and begin to
oscillate in accordance with the frequency.
• Oscillation causes friction which generates heat within the
food stuff.
• Ex: microwave heating.

11. Thin layer drying
• Process in which all grains are fully exposed to
the drying air under constant drying conditions
i.e. at constant air temp. & humidity.
• Drying rate is independent of air velocity.
• Up to 20 cm thickness of grain bed is taken as
thin layer
• All commercial dryers are designed based on
thin layer drying principles.

12. Deep bed drying
• All grains are not fully exposed to the same condition of drying air.
• Condition of drying air changes with time and depth of grain bed
• Rate of airflow per unit mass of grain is small
• Drying of grain in deep bin can be taken as sum of several thin layers.
• Humidity & temperature of air entering & leaving each layer vary with time
• V
olume of drying zone varies with temp & humidity of entering air,
moisture content of grain & velocity of air

13. Type of dryers

14. Flat bed type batch dryer
• This is a static, deep bed, batch dryer.
•Simple in design and most popular on farm.
Construction:
• It is a rectangular box type dryer.
• Size of dryer depends on area of the supporting perforated screen on
which grain is placed.
• Holding capacity- 0.25-1 tonn/batch.
•Motor capacity- 0.25-1 hp.
Operation:
• Grain is placed on supporting screen and heated air is forced through
the deep bed of grain.
• After desired moisture content observed, grain is discharged mannualy.
• Temperature of heated air should be limited upto 45oC.
• Air flow rate- 20 to 40 m3/min/1000kg of raw paddy on initial moisture
content.

15. Tray dryer
• In tray dryers, the food is spread out, generally quite
thinly, on trays in which the drying takes place.
• Heating may be by an air current sweeping across the
trays, or heated shelves on which the trays lie, or by
radiation from heated surfaces.
• Most tray dryers are heated by air, which also removes
the moist vapors.
• Many shallow trays are kept one above other with a gap
between.
• Tray may or may not have perforated bottoms.
• Generally used for vegetables and similar perishables.

16. • This is traditional method of drying of crops and
grains.
• Using the energy of the sun to remove moisture from
the product.
• Traditional sun drying
• Mechanical solar drying
Solar drying

17. CONCLUSION
• As shown different food products should be
stored at different moisture contents.
• If moisture content is more than the optimum
deterioration increases resulting in great loss.
• Therefore, dryers play an important role in
these days where food security is one of the
major problem.