March 1, 2023 | 10 min read
Modern Rice Milling Process: Meaning, Steps, and Flow Chart
Rice processing is extremely important for India, as it is a regular staple food for many. Rice processing, to put it simply, is a process that involves machines that clean, remove dirt, take off unnecessary outer layers, grind, soften, and sort the rice to make it edible for people.
After all of this, the rice that is obtained is free of impurities and has a minimum number of broken kernels. After the rice milling process is done, the final product is usually 60-65% white rice, 8-10% bran, 15% husk, and 5-10% are impurities like stones and sand. These change depending on the quality of paddy that is used for processing.
Now that you know what rice processing is, let’s see the steps involved in it.
The usual rice processing steps are:
1. Paddy Pre-cleaning
Before dehusking the rice paddy, it is important to remove the unwanted dirt that comes with it. This dirt is usually in the form of weed, straw, soil, rocks, seeds, and other inert materials, which, if processed with rice, can reduce the efficiency of the huller.
The machines used for this step are called a rice cleaner, a rice rotary vibrating screen, and a rice destoner. The capacity of the paddy pre-cleaner should be 1.25 times the remaining mill machines.
Apart from removing unnecessary dirt, this process is also important as it increases the percentage of oil in bran, which is extremely good for your health.
2. Dehusking / Dehulling
Dehusking, or dehulling, is the process of removing the husk from the paddy, which leads to the production of brown rice.
The Husk is the outer part of the rice that is removed by friction as the paddy grains or the husking rice pass between two rough surfaces that move at different speeds. After this process, the husk is removed by suction and transported outside the mill, usually to a storage dump. This is called paddy separation.
You can check the efficiency of a rice processing machine by checking its dehusking efficiency. An efficient one, on average, removes at least 90% of the husk in a single pass. It is also important to note that husk accounts for about 15% of the paddy weight.
3. Paddy Separation
This is another step where you can check the efficiency of a paddy separator (also known as a husker). Before we move on to how to check its efficiency, let’s see what it does. As the name implies, the paddy rice separator separates unhusked paddy rice from brown rice. This unhusked paddy rice is usually called "residue."
If the amount of paddy present is less than 10%, then you can be assured that your husker or paddy separator is a good one. Paddy separators work by taking advantage of the differences in buoyancy, specific gravity, and size between brown rice and paddy. Husker or paddy separators make it easy to go ahead with the next process in modern times.
4. Rice whitening or polishing
While we did see the production of brown rice in the previous step, here you’ll see how white rice is made. The process is actually super simple and involves just removing the bran layer and the germ, resulting in white rice.
The outer layer of rice, called bran, is removed from the kernel by using special machines that use abrasives or friction. Usually, 8–10% of the total weight of the rice is removed during this process. To prevent the rice from breaking during the next step, it is passed through two to four machines that further clean and polish the rice. These machines are connected in a series.
At this stage, the surface of the rice is smoothed out further by removing the remaining bran particles and polishing the exterior of the milled kernel. This is done by using a humidified rice polisher.
5. Rice grading
At this stage, the broken rice is separated from the whole rice using a machine called a cylindrical indented screen. This machine separates the broken rice by rotating at a specific speed.
While the amount of rice that is broken should be minimal and often depends on the customer's requirements, it is important to note that a good rice mill will produce 50–60% head rice, 5–10% three fourth broken rice, and 10-15%half broken rice. A volumetric mixer is then used if the rice needs to be mixed together.
After the rice is polished, it is separated into different categories, like head rice, large broken rice, and small broken rice. This process is done using an oscillating screen sifter.
A length grader can be installed for more precise separation.
6. Colour sorting
Rice colour sorting machines are used at this stage to separate the discoloured rice grains from the coloured ones. This further improves the quality of the rice.
7. Rice weighing and bagging
The final step in the process is to package and weigh the rice. While the majority of rice mills use manual, mechanical weighing systems, some use more advanced electronic weighing systems.
Rice is usually sold in 25 or 50 kg bags that need to be accurately labelled and weighed. The weighing systems ensure that the rice is accurately weighed and packaged for easy transportation to the customers.
After the packaging process, the rice is then stored by the automatic packing machine itself. If you want to sell rice that's high quality and get better profits, it’s important to use advanced machinery like a mill in the rice milling process.
While these steps do sound overwhelming, modern rice machine equipment has made them easier for people. You can buy any of the above machines at One of India’s best ISO 9001:2015 Certified Company - Suriengineers