During the rice milling stage, rice grains move through a multifarious process. It's ushered through a number of sorting machines, wherein the grains are sufficiently processed.
Why is milling important?
Since rice is not fit for human consumption in its raw form, ie paddy, the need for processing arises. As such, milling is a critical post-production step which single-most important objective is to obtain it in its edit form, free from impurities.
Ideally, rice milling involves the removal of husk and bran to produce an edible white rice kernel that is not only sufficient milled but is edible too.
As per the customer requirement, processed rice should have a certain minimum number of broken kernels. Let's take a closer look at rice kernel composition:
Typically, rice varieties are composed of about 11% bran layers, 20% rice hull / husk and 69% starchy endosperm, which is also referred to as total milled rice.
With varying durations, there are roughly 3 different processes involved in the milling, sometimes single step process, two-step process and multi-stage process.
Single Step Milling: Under this process the husk and bran layers are removed in a single go.
Two-step Milling: Bran and husk are removed separately in two different settings.
Multi-stage Milling: Under this process, paddy is ushered through a number of different processes. The objective of this process is to reduce mechanical stress and prevent heat buildup within the grain. This ensures that there is no grain breakage and uniformly polished grains are produced.
The different steps involved in the process of multi-stage rice commercial milling are:
1. Paddy Pre-cleaning: This process essentially removes undesired foreign materials such as unfilled and uneven grains, impurities, sand, straw, clay, etc. Rice is passed through a series of aspiration systems and sieves.
2. Paddy De-stoning: Se-stoning is the process of separating rice grains from stones. This process works on the principle of gravity wherein the rice, being lighter stones, fluidizes into air gradient, leaving behind the heavier stones.
3. Paddy De-husking / dehulling: Based on centrifugal principle, dehusker machine removes the husk layer from paddy.
4. Paddy separation: As compared to a paddy, the surface of rice is smoother. This difference in texture is used to separate brown rice from paddy.
5. Rice Whitening: Rice whitening is the removal of bran and germs from brown rice through an efficient aspiration system
6. Rice Polishing: This step involves the removal of the remaining bran particles and then polishing the exterior of kernel by a humidified rice polisher.
7. Rice Length Grading: During this process, the broken rice is removed from the whole rice, and small and large head brokers are separated from the head rice.
8. Rice Blending: In this process, head rice is combined with predetermined amount of brokers, as per customers' requirements.