This document describes the process of par-boiling rice. It involves soaking rice to allow absorption of water, steaming the rice to halt the soaking process, then drying the rice. Par-boiling makes the rice firmer, less sticky, and easier to mill. The document outlines the main equipment used in par-boiling systems and provides details on the specific processes for single boiled, double boiled, and cured/steamed rice varieties. It also discusses drying methods and considerations for maintaining rice quality during drying.

1. Par-boiling & Drying
E.Jayakumar, B.E (Mech).,M.Tech (FPE).,MIE.,FIV.,
Charted Engineer (India)(M-153913-7),
Approved Valuer (F-25667)(VII)-Machinery and Plant .
Free Lancer,
AGRO TRADE LINK
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E.Mail: jayakumaryuan@gmail.com: Mobile: +91 9444025375, +919940819765
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2. Par-Boiling
 Partial cooking of rice intact with husk is called
parboiling.
 Involves soaking, steaming, drying and milling.
 Parboiled rice takes less time to cook and is firmer and
less sticky

3. Advantages
 Milling
• Dehusking is easier and costs less
• Fewer broken
• Increased head and total rice output
 Storage
• More resistant to insect attack
 Cooking
• Loses less starch and keeps longer
• More fiber than regular rice

4. System
 Material feeding (Elevator)
 Pre Cleaner
 Over Head Storage
 Soaking Tanks
 Steaming tanks
 Water Pipe line
 Steam pipe line
 Drainage system
 Water circulation system
 Material discharge (Belt Conveyors)
https://www.youtube.com/watch?v=rFbCkD
0Eb0Q

5. Processing
Soaking
Impregnating moisture to the required level before cooking
operation.
Steaming
Raising the temp of paddy to near saturation temp of water in
the presence of steam.
Drying
The paddy is left at high temp and moisture level of 32%
At his stage the paddy is liable for bacterial and fungus attack
Hot aid blown through it in the dryers
It involves lot of techniques to get uniformly dried grain with desired
moisture

6. Techniques
 Single boiled rice (white belly rice)
 Double Boiled Rice - Fully translucent rice
 Hot soaking method - Fully translucent rice
 Steamed rice (Cured rice)

7. Process for Single Boiled Rice -White belly Rice
Pre-cleaning
De-stoning
Transfer to overhead bins
Discharge raw paddy in to room
temperature water in soaking tanks
MS/SS Soaking Tanks
Remove chaff and immature grains
floating on water surface
Soak for 6 to 12 h
(Capacity: 2-3 tones with steaming and water circulation arrangement)
Capacity of tank 2-3 tones
With steaming and water circulation
arrangement.
or
Soaking tank capacity of 5-10 tones

8. Process for Single Boiled Rice -White belly Rice Cont..
Circulate the water Drain and tempering for 2 h
Steam the paddy for 1 to 2 min after
steam emergence on top
Discharge the paddy quickly from
steaming tank into cooler
Dry the paddy in Drier
(Circulatory/ fluidized bed type cooler)
(Moisture content to 14%)
Unload the paddy to Storage bin / Milling Section
If 5 – 10 tones soaking tank, steam the
soaked paddy in steaming vessel of
capacity 0.5 to 1.0 tone / continuous
steaming vessel kept below the soaking tank
Number of tanks matching the drier capacity

9. Process for Double Boiled Rice - Fully translucent rice
Pre-cleaning
De-stoning
Transfer to overhead bins
Discharge raw paddy in to
soaking cum steaming tanks
MS/SS Soaking Tanks
Steam for 5 min
Add water RT water to steamed paddy
(1.5 times to the paddy)
Capacity of tank 2-3 tones
With steaming and water circulation
arrangement.
or
Soaking tank capacity of 5-10 tones

10. Process for Double Boiled Rice Cont..
Circulate the water for half an hour
Remove floating chaff and immature
Soak for 12 to 24 hrs depending on the Variety
till complete saturation of paddy
Drain the water and temper for 2 hrs
Unload the paddy to Storage bin / Milling Section
Steam paddy for 1 to 2 min after
steam emergence at top
Discharge the paddy quickly from
steaming tank into cooler
Dry the paddy in Drier
If 5 – 10 tones soaking tank, steam the
soaked paddy in steaming vessel of
capacity 0.5 to 1.0 tone / continuous
steaming vessel kept below the soaking tank
Number of tanks matching the drier capacity

11. Process for Hot soaking Method - Fully translucent rice
Pre-cleaning
De-stoning
Transfer to overhead bins
Pump hot water 95ºC in to soaking tank or
Inject steam into RT water in soaking tank to raise
Temperature to 95ºC
Discharge raw paddy into hot water
Circulate for ½ h so that the hot soak water attains 650C
Soak for 3 to 5 h according to the paddy variety
Drain water and temper for 2 h
Capacity of tank 2-3 tones
With steaming and water circulation
arrangement.
or
Soaking tank capacity of 5-10 tones

12. Process for Hot soaking Method Cont..
Steam for 1 to 2 min after emergence of steam on top
Quick discharge of steamed paddy from steaming
tank to cooler
Dry the paddy in Drier
Unload the paddy to Storage bin / Milling Section
If 5 – 10 tones soaking tank, steam the
soaked paddy in steaming vessel of
capacity 0.5 to 1.0 tone / continuous
steaming vessel kept below the soaking tank
Number of tanks matching the drier
capacity
Circulatory/fludised bed type cooler
IBR Boiler

13. Process for cured/steamed rice
Discharge raw paddy in to
soaking tanks
Steam for few min as per requirement (5-15 min)
Transfer to Tempering bin (3-4h)
Drying
(Hot air temperature 65°C)
Temper the paddy for 12 h before milling
IBR Boiler
Curing
The accelerated effect of ageing in rice is
called curing. It can be achieved by steaming of fresh
paddy /paddy stored for few months.

14. Drying
 Grain Drying Principles and methods
◦ Reduce the moisture from grain to a safe level of storage .
◦ It is a critical step for maintaining grain quality and minimize
the storage and processing losses.
◦ Drying is need because the high moisture grain will cause heat
build up (Hot spot) from respiration of microorganisms, low
thermal diffusivity of grain ,increased the mold growth, reduced
starch and sugar content.

15. Why drying need?
High moisture grain will cause :
Heat build - up (Hot spot)
 From respiration of microorganisms and grain itself
 Low thermal diffusivity of grain
 Increased the temperatures accelerate the mold growth,
 Reduced starch and sugar content.

16. Drying mechanism
 Two fundamental steps occur during drying
◦ Water migration migration from grain interior to surface.
◦ Water evaporation from the surface to the surrounding air.

17.  Moisture content decreases rapidly at first but slows
down as grain dries.
 Drying rate decreases with moisture content increases
with air temperature.
 Removal of water from grain during drying causes a
reduction in grain quantity
 Moisture content can be calculate :
Drying mechanism
Moisture Shrink % =

18. Equilibrium moisture content:
 During drying, moisture content depends on temperature
and relative humidity of surrounding air
 When surrounding air is “dry” grain would loss
moisture.
 When surrounding air is “humid” grain would
absorb moisture

19. Drying air Properties :
 Vapor Pressure
◦ Partial pressure exerted by the water vapor molecules in moist
air.
 Relative humidity
◦ Ratio of the mole fraction of water vapor in the air to the mole
fraction of water vapor in saturated air
 Humidity ratio
◦ Mass of water vapor per unit mass of dry air

20.  Dry bulb temperature
◦ Air temperature indicated by an ordinary thermometer
 Wet bulb temperature
◦ Air temperature indicated by thermometer whose bulb is covered
with a wet wick
 Dew point temperature-
◦ Temperature at which moisture condensation will occur as air is
cooled
Drying air Properties :

21.  Enthalpy-
◦ Heat content of the moist air per unit mass of dry air above a
certain reference temperature.
 Specific volume
◦ Volume per unit mass of dry air.
 Specific Heat
◦ Measurable physical quantity of heat energy required to change
the temperature of air by a given amount.
Drying air Properties :

22. Effect of Drying on grain qualities:
 Low and uniform moisture content
 Minimum broken and damage kernels
 Low susceptibility to subsequent breakage
 Retained nutritional value
 High viability
 Good visual and organoleptic properties.

23. Drying Methods
 Sun drying
 Mechanical Drying

24. L.S.U 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
 Consists of rectangular chamber, holding bin, blower with
duct, grain discharging mechanism and air heating system
 Layers of inverted V shaped channels are installed in the
drying chamber; heated air is introduced through these
channels at many points
 Alternate layers are air inlet & outlet channels; arranged one
below the other in an offset pattern
 Inlet port consists of few full size ports & two half size ports;
all ports are of same size arranged in equal spacing
 Ribbed rollers are provided at the bottom of drying chamber
for the discharge of grain

25. L.S.U Dryer
1. Garner
2. Duct
3. Dry material outlet
4. Hopper
5. Continuous flow
6. Door
7. Roof

26. Process
 Dry the paddy at 100°C of Hot air till the on line moisture meter
shows 20%
At the moisture of 18-17% transfer the paddy to tempering bin( 3-4 h)
Reduce the hot air temperature to 80°C
till the paddy moisture percent falls to 14 -13%
Temper the paddy for 12 h before milling

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Phone: 04362-278398 :,Skype: Easupatham