it include a brief idea about the different dryers used for the onion drying and their specificationns

1. ONION DRYING
BLESSY .V. A
2011-02-014
S6
BLESSY V.A.
2011-02-014

2. • Scientific name - Allium cepa
• Pungency - allyl-propyl disulphide
• Contains vitamineB,vitamineC,iron and calcium
• Medicinal value – antimicrobial,
antiasthmatic,antitumor and anticancer effect

3. • Third rank in the world production
• World production - 64.48 million tone
• Highest production is in Ireland (58t/ha)
• Maharashtra is the leading producer In India (5.04 MMT )
• India is the second largest producer of dehydrated
onion(700 tone)

4. Particulars(g) Before drying(per
100g)
After drying(per
100g)
moisture 86.6 4.6
protein 1.2 10.6
fat 0.1 0.8
minerals 0.4 3.5
fiber 0.6 6.4
carbohydrate 11.1 74.1

5. • Drying of onion helps to increase shelf life
• Onion dried from initial moisture content of 86%(wb) to
7%(wb) or less
• Storage temperature(0-2.3°C)
• Storage relative humidity(30-70%)

6. • Solar onion dryer
• Convection air dryer
• Fluidized bed dryer
• Infrared dryer
• Vacuum dryer
• Freeze dryer
• Microwave dryer
• Osmotic dehydration

7. • Forced convection type
• Drying is due to convection and conduction

8. • Solar dryer developed at Sardar Patel renewable
energy research institute(SPRERI)
Loading capacity 100kg/batch
Moisture content Initial 85% to final 2-5%
Operating
temperature
65°C
Source of heat Glazed solar air heating collectors(72m²)
Drying duration 4hrs
Installed in 1995

10. • Used Commercially
• Keep organoleptic characteristics of onion
• Excessive thermal damage is the main problem

11. • Air temperature range - 50°C to 80°C
• Relative humidity of air - below 20%
• Air velocity - 27m/min
• Slice thickness - 3mm
• Duration - 1 hour

13. • Used for - onion flakes, slices
• It permits continuous, large scale drying of food materials
without over drying.
• High rate of heat transfer
• Low maintenance cost
• vibrated type fluid bed is used

14. • High heat and mass transfer rate
• Duration - 15 minutes
• Depth of onion bed - 75mm
• Thickness of onion slice - 1 to 5mm

16. • Heat energy is produced due electromagnetic radiation
• Catalytic infrared dryer is used
• Natural gas used - propane
Advantages
• High quality
• Product - white in color
• Rehydration is very easy

17. • Drying temperature - 80 °C to 70°C
• Initial temperature - 80°C
• Thickness of slice - 6mm
• Mainly infrared power level affect Drying rate
• Air circulation do not affect the drying rate

19. • Drying - low pressure , low temperature , low oxygen
environment
• Thickness of the onion layer - 1 to 5mm
• Drying temperature - 50°C to 70°C
• High quality product

20. VACCUM TRAY DRYER

21. • Moisture removal due to sublimation
• Laboratory purpose : -30 °C to -40°C
• Commercial purpose : -20°C
• Onion thickness : 4 to 6mm
• Duration : 7 to 8 hours
• Pressure : 6.1mm Hg

22. FREEZE DRYER

23. • Low energy consumption
• Heating is more rapid

24. • Drying due to osmotic pressure difference
• Salt concentration – 20%
• Temperature - 28°C
• Duration – 1 hour

25. “For the purpose of onion drying we can use
different dryers but the cost , time of operation ,
product quality is varying with different type of
dryers”