Table of Contents
What is parboiling process?
Parboiling is a hydrothermal treatment process of soaking, steaming and drying of the paddy, which is performed before the milling operation.
The two main ingredients used in the parboiling process are: Water and Heat. The primary purpose of this entire process is to increase the head rice yield and reduce the breakage of the rice grain during the milling process.
Paddy undergoes various mechanical stages of harvesting, threshing, drying, dehulling and milling, which forces rice grains to crack under tension and increase the percentage of broken rice during final output. Consequently, broken rice brings market losses, price reduction, decreased product output from milling procedures, and storage issues.
Therefore, the parboiling process revolutionized the paddy production industry and became the only solution to reduce the breakage of rice. In summary, the hydro-method of parboiling causes the paddy to produce a gel-like substance inside the starch. This process is called gelatinization, where it heals all the fractures and also strengthens the rice grain which, in result, increases the total yield of the rice production during polishing. It gelatinization also de-localize the rice grain inside the husk which makes it easier to separate edible rice from its husks during the de-husking process.
In fact, though, the method of parboiling was developed with a preliminary objective of hardening the kernel to maximize head rice yield in milling. Moreover, it was later scientifically discovered the nutritional value and health benefits of consuming parboiled rice compared to raw rice which created the awareness and importance of parboiling among consumers and manufacturers worldwide, particularly in Asian countries and the estimated percentage of parboiled rice production in India is about staggering 60%, making them a most preferred rice type compared to non-parboiled rice.
Steps of parboiling process:
The parboiling process involves soaking, steaming and drying. The soaking increases the moisture content in the paddy and steaming causes gelatinization of starch and increases the grain strength.
There are various parboiling techniques for paddy. Here we will look at the basic steps involved in paddy processing.
Soaking:
Once the paddy is cleaned and de-stoned, the initial parboiling process involves water soaking the paddy for a certain period of time. During the soaking stage, the water molecules penetrate through the micro-pores of husk and are absorbed by starch granules to become moisture hydrated and swell inside the husk, making it loose in the process.
At the same time, micro-toxins- which are naturally occurring unsafe residues, produced by certain fungi are entirely dismantled and wiped-out at such high levels of moisture content. This moisture saturation also activates enzymes in the paddy.
The moisture content of soaked paddy is about 30%-35%. The soaking duration can be minimized by maintaining a constant water temperature. Elevated temperature also reduces steaming time. Even steaming time can be cut-down by continuously recirculating and reheating of the water. Moisture content in the soaked paddy is about 30%-35%. For better soaking, paddy grain size should be uniform.
Steaming:
After the soaked paddy drained from the container and then transferred to the steaming container. Steam is pressured between 0.5 – 3 bar depending on the paddy type. At this process, the moisture content in the grain gelatinizes the starch during the steaming process which causes physico-chemical reactions such as pigment transformations and enzymes deactivations. This brings improved flavor, color change and cooking characteristics of the rice.
Moisture content of paddy increases to 38% during steaming as a result, the splitting of the husk indicates completion of the steaming process, however, splitting is not a necessary condition and paddy can be completely parboiled without any splitting.
Drying:
Drying evaporates the moisture and compresses the gelatinous starch together in a compact mass and delocalizes it from the husk making dehusking (milling) easier. Process of drying will also stop microbial pathogens from developing on steamed paddy.
Major Benefits of Parboiling Rice Process
Major Benefits of Parboiling Rice Process
1. The milling yield and the quality of rice increases as There are less broken grains.
2. Dehusking is easier and costs less (Higher productivity of rubber rolls compared to raw paddy dehulling)
3. The parboiled-milled rice becomes translucent and shining.
4. Germination is no longer possible and the endosperm has a compact texture making it resistant to attack by insect and microorganism
5. The grain remains harder during cooking and less likely to become sticky.
6. It reduces the breakage rate during the husking process.
7. Reduces the loss of nutrients during washing.
8. A greater amount of water is absorbed during cooking causing the rice to swell.
9. After cooking the rice absorbs less fat from added condiments, the rice keeps longer and does not become rancid easily.
10. Parboiled rice retains more proteins, vitamins and minerals.
11. Shelling of parboiled paddy is easier.
12. Parboiled rice is more digestible and less solids are left behind in the cooking water.
13. Bran of parboiled rice has more oil
14. Cooked parboiled rice has a better digestibility ratio because of its texture and firm consistency. After cooking, the grains are firmer and tend to be less sticky.
Conclusion:
Rice is one of the cereals that belongs to the grass family and considered as an important plant for the supply of staple food to over half of the world’s population. In general, rice is considered as the source of carbohydrates and supplies energy to the body through diet. The parboiling paddy process plays a crucial role in both retaining the nutritional content in the rice kernel and reducing the rice breaking during the milling operation.
