Parboiling means, precooking of rice within the husk without disturbing its size and shape. A hydrothermal treatment resulting partial cooking (gelatinization of starch) of paddy (rough rice). The process consists of soaking rough rice in water until it is saturated, draining the excess water, and then steaming or otherwise heating the grain to gelatinize the starch

1. Paddy Parboiling
PARBOILING OF RICE
BY
ISHFAQ MOHI U DIN
M.Sc. FOOD SCIENCE AND TECHNOLOGY
UNIVERSITY OF KASHMIR
Enrolment No. 17049110015
E mail: beingsahilishfaq@gmail.com
eshfaqbhattft@gmail.com

2. Parboiling
 Parboiling means, precooking of rice within the husk without disturbing its size and
shape.
 A hydrothermal treatment resulting partial cooking (gelatinization of starch) of paddy
(rough rice).
 The process consists of soaking rough rice in water until it is saturated, draining the
excess water, and then steaming or otherwise heating the grain to gelatinize the
starch.
 During parboiling irreversible swelling and fusion of starch granules occurs and
changes starch from crystalline to amorphous form.
 Parboiling reduce breakage and loss of minerals & vitamins.
 About 60% of total production of paddy is parboiled in India.
 It is estimated that about a fifth of the world’s rice is parboiled.

3. Process :
 Step 1: Pre Steaming (First Steaming/Soaking)
 Step 2: Soaking
 Step 3: Post Steaming (Second Steaming)
 Step 4: Drying and Tempering

4. Pre Steaming (First Steaming/Soaking)
 First step in conventional parboiling, involves hydrating the grains sufficiently to enable
gelatinization on subsequent heating.
 Hydration is a diffusion process, its rate increases with increasing temperature.
 At low water temperature, hydration is too slow and also comes to an equilibrium, causing bacterial
action.
 On the other hand, too high temperature is also undesirable. At high temperatures, the rate of
hydration, after an initial lag period, increases exponentially, results into the splitting of the hull.
 Splitting occurs only at temperatures above the gelatinization point, as gelatinized starch absorbs
more moisture.
 The optimum moisture content to which rice is soaked is 30 – 32%. Beyond this level, the hull splits
open as it may not be able to contain expanded endosperm.
 The optimum temperature for soaking is 60° C or less where the equilibrium moisture content does
not exceed 30% and there is no need for care & control of the soaking period.

5. Pre steaming (First steaming) Strategy
 Pre steaming before soaking softens the paddy, to achieve desired color of
parboiled rice
 Increases the temperature of the paddy and reduces the soaking time of the paddy
 Increases the capacity of par-boiled rice to absorb water during cooking
 Industrial practice of pre-steaming time is 2 to 4 minutes
 Steam temperature is 100 –110° C during the first steaming
 Energy required in steaming 1000 Kg of paddy: 24.42 kWh (21,000 kcal)
 Use of Steam Flow Meters will improve energy efficiency
 To get uniform quality and high efficiency steaming to be automated

6. Paddy Soaking
 Soaking is a diffusion process
 The diffusion pressure of dry paddy is zero and porosity is about 48%
 Difference in vapour pressure between paddy and water results movement of water in to Paddy during
soaking
Step 1: Water molecules first adhere to the husk surface and then penetrate through
microspores of husk
Step 2: Water is retained in the voids of rice kernel due to capillary absorption
Step 3: Water molecules will be absorbed in starch granules and held as water of
hydration
 Commonly practiced soaking of paddy in hot water for 6-10 h at 70C°
 1.3 cubic metre of water is consumed per metric ton of paddy
 Moisture content of soaked paddy is about 30%-35%
 Energy required in soaking is used in raising the temperature of water from 25°C–
85°C:83.72kWh Heat energy
 Soaking at elevated temperature prevents mycotoxins and also reduce the steaming time.

7. Parboiling process flow

9. Strategy for Efficient Paddy Soaking
 Paddy grain size should be uniform
 Continuous recirculation, reheating coupled with aeration reduce the soaking time
 Optimum time-temperature combination for single stage soaking: 6 h - 65°C
 Accelerated can be achieved at soaking water pH(11)
 Two stage soaking (67% time reduction compared to single-stage soaking)
 Stage 1: Soaking at 80°C/45 min and moisture content of 35.0% dry basis.
 Stage 2: Soaking at 70°C/195 min and moisture content of 42.7% dry basis.
 Heat from effluent after soaking can be used for preheating the fresh soaking water.

11. Post Steaming (2nd Steaming) of paddy
 Steaming is carried out to gelatinize the starch
 Saturated steam at a pressure of 1-5kg/cm2 is used for steaming of soaked paddy
 Splitting of husk is indication of completion of steaming
 60 kg of steam is required to steam 1 ton of paddy
 Moisture content of paddy increases to 38% (wet basis) during steaming
 24.42 kWh (21,000 kcal) of energy is required in steaming 1000 Kg of paddy
 Improves grain length and uniforms the color of Par-boiled rice
 Steam temperature has a considerable effect on the color of parboiled rice.
 The color of rice is due to pigments of husk, bran and absorption of reducing sugar
that react with amino acids

12. Post Steaming (2nd Steaming) Strategy
 Keeping steamed paddy in a heap on the drying floor is equivalent to
prolonged steaming and results in dark colouring of rice
 Steaming of paddy completes once steam emerges after for 1 to 2 min
steaming of the batch
 Steam at a pressure of 0.5 atm is used for the second steaming of paddy
 Time of gelatinization can be shortened by increasing superficial
superheated-steam velocity
 Energy efficiency in steaming can be achieved by using low pressure steam

13. Drying of Paddy
 Drying of parboiled paddy from 45-50% (dry basis)to14-16% (dry basis) needs to be
done for proper milling and storage
 The first drying period takes about three hours including dryer loading and unloading
time. After tempering, the second drying period takes about two hours.
 159.30 kWh of energy required in drying 1000 kg of Paddy at 80°C and airflow of 50
m3/min for drying upto 4 hours
 One of the main reasons for rice kernel breakage is fissures which is developed due to
Moisture Content gradients occurred during drying

14. Drying Strategy
 Paddy to be dried slowly in two passes instead of continuous drying. In first pass,
paddy moisture content should e brought down to 18-20% and rest in second pass.
 Double-pass drying with tempering saves upto 45% of drying time compared to
single stage drying
 Tempering of 120 min at50°C reduced fissuring by 32 to 50%
 Use of online moisture meters will help in quality control of rice
 The efficiency of dryer blowers should be studied
 Heat recovery from dryer condensate
 Pressure drop across the dryer to be avoided

15. Double-pass drying of parboiled paddy with and without tempering

16. Factors controlling the quality of parboiled rice
 Soaking time and temperature
 Steaming pressure, velocity, time and stages
 Tempering time and drying time
 Drying temperature and stages

17. Advantages of Parboiling
 Overall increase in total rice recovery is about 6%.
 Contains high nutrients (B vitamins and Minerals) as compared to raw rice
 25% more oil in the bran compared to raw rice bran
 Dehusking is easier and costs less (Higher productivity of rubber rolls compared to raw
paddy de-hulling)
 Germination is no longer possible and the endosperm has a compact texture making it
resistant to attack by insect and microorganism
 Reduced loss of nutrients and solids during washing
 Insect infestation and loss of nutrients during storage is reduced
 Parboiled rice is suitable for making three rice products (canned, puffed, and flaked rice)

18. Disadvantages
 More time and energy required for bran removal.
 A great amount of water is absorbed during cooking causing the rice to swell.
 High BOD(1350-1800ppm) of Effluent water.
 The mill screen tends to get choked during its whitening.
 The flow and packing properties of undermilled rice are poor.
 The rice needs more time and energy to cook.
 Its harder texture after cooking is not liked by many consumers.
 It is more prone to oxidative rancidity.

19. THANK YOU