Rice husk constitutes to be the largest by-product of rice milling and one third of the paddy by weight consists of rice husk. Rice husk has a considerable fuel value for a variety of possible industrial uses. Hence, the major use of husk at the moment is as boiler fuel, wherever parboiling is practiced. Rice husk is tough because of its silica-cellulose content. The silica content is husk is the highest among plant offal. It contains 15 to 18 % silica; therefore, it is a potent source of silica for the manufacture of silicates or in glass manufacture. Also pulverized husk is available wherever paddy is parboiled and it is mixed with other mill fractions as cattle feed. Pulverized husk has a low feed value and it has low protein content. It contains more than 30% crude fibre. If nitrogen content in pulverized husk is increased by blending with other nitrogen rich feeds and fibre content is brought down to around 10%, pulverized husk can be used as cattle feed on large scale.
Rice Bran is the most valuable by-product of the rice milling industry. It is obtained from the outer layers of the brown rice during milling. Rice Bran consists of pericarp, aleurone layer, germ and a part of endosperm. Rice bran obtained during milling amounts to 4 to 9% of the weight of paddy milled. True bran amounts to 4 to 5% only and rest is polishing of inner bran layers and portion of the starchy endosperm.
Rice bran can be classified into two groups –
Rice bran can be utilized in various ways. It is a potential source of vegetable oil.
Raw rice bran contains 12-18% oil, whereas parboiled bran contains 20-28% oil. The de-oiled bran contains about 1 to 3% oil only. Rice bran also contains high fat and protein. It also contains vitamins, minerals and many other useful chemicals. Because of its nutritional value, it is being used as feed for poultry and livestock. In fact full fatted bran is an excellent ingredient for both food and feed.
Broken rice is another by-product of rice milling industry. From the nutritional point of view, broken rice is as good as whole rice itself. Broken rice has low economic value as compared to whole rice. Generally, broken rice is of poor quality due to admixture with grit, stones and clay particles. Therefore, broken rice is used either as a part of animal feed or partially in the diet of poor people. If the quality of broken rice is improved by cleaning the paddy properly before milling, it can be utilized and marketed straightway for preparation of Idli, Dosa and other such preparation in which rice flour or wet-ground rice paste is needed.