Milling of rice (Conversion of Paddy to Rice)
It includes all the steps involved in conversion of paddy to rice.
3.1 Pre-cleaning: removing all impurities and unfilled grains from the paddy
3.2 De-stoning: separating small stones from the brown rice
3.3 Husking: removing the husk from the paddy
3.4 Husk aspiration: separating the husk from the brown rice/unhusked paddy
3.5 Paddy separation: separating the unhusked paddy from the brown rice
3.6 Whitening: removing all or part of the bran layer and germ from the brown rice
3.7 Polishing: improving the appearance of milled rice by removing bran and by polishing the exterior of the milled kernel
- Rice bran
- Rice Bran Oil
3.8 Length grading: separating small and large broken from the head rice
3.9 Color Sorting: Separating on the basis of colors
3.10 Blending: Mix head rice with predetermined amount of broken, as required by the customer
3.11 Weighing and bagging: Preparing milled rice for transport to the customer
The paddy rice is passed through coarse screens to remove all straw, stones, and other objects that are larger than the rice. The rice passes over fine screens to remove small weed seed, sand and dirt, stones, and other objects smaller than the rice. Air separation systems are sometimes used in this process.
The rice is passed through a specific gravity table that separates the product by density. Stones are separated from the rice.
The husk is removed from the rice. This is most often done by passing the rice through two spinning rubber roles. One roll is spinning faster than the other. The rubber rolls are tightly pressing against the rice from both sides and strip the husk off.
A portion of the rice leaving the husking operation still has the husk on the kernel. A paddy separation machine that works with specific gravity separates the light paddy kernels from the heavy brown (husks removed) kernels. The paddy kernels go back to the huskers.
There are many machines and methods designed to remove bran from the rice. The Japanese milling system is most often used in the most modern mills. With this system, the rice is first passes through a milling chamber that has an abrasive stone spinning in the center and a scarified metal screen on the outside. (The abrasive system). The rice then passes through a milling chamber that has a metal roller spinning in the center and a scarified metal screen on the outside. This machine is rubbing the many kernels of rice against themselves and the screen in order to remove the bran. (The frictional system.) The last pass (sometimes all frictional passes) is basically another frictional machine that is applying a mist of water to facilitate milling and add a smooth polished surface to the rice. (The water polishing system.) This Japanese system can be done in three passes as described here, or as many as seven passes.