Second process is removal of bran layer which also remove germ and partial portion of the endosperm. White rice is produced from brown rice by removing the bran layer and the germ. The bran layer is removed from the kernel by applying friction to the grain surface either by rubbing the grains against an abrasive surface or against each other.
Polishing of rice kernel is very vital step in rice processing to remove bran. Although the extracted bran becomes a valuable by-product as a good source of edible oil, the nutritive value of polished rice kernels gets reduced considerably including significant loss of natural fiber.
The process used to whiten brown rice can be classified as either abrasive or friction. In abrasion method, this process the grain is whitened by the abrasive action of the rice kernel passing between a moving abrasive surface and stationary screen. The hard-rough surface is usually stone or a carborundum type material. The abrasive process applies less pressure on the grain and is better suited for long grain varieties.
In the friction whitener the grain kernels are forced against each other and a metal screen by a steel-ribbed cylinder rotating inside a metal-plated cylinder.
Prior to the advent of modern polishers, several traditional methods have been used to polish rice. These methods include: pounding in mortar with pestle; beating with clubs on the floor; rubbing on the floor; beating gently with clubs in jute bags and threading under the feet of man or hooves of animals.
Rice polishing
