Oryza sativa

Rice (grain)

Of the many varieties, swamp rice, which requires flooding for two to three months during its growth, is the most important. Mountain, or upland, rice requires less irrigation. After threshing, the rough rice is transported to mills for processing into white rice (polished rice) through a series of operations that free it from the hull, germ and bran. In many countries the processing of rice for local use is still carried out in one-stage mills. The by-product of this simplest form of processing is a mixture of hulls and bran that seldom reaches the market as it is usually returned to the rice grower. In large-scale mills the rough rice undergoes several processes: cleaning, parboiling, hulling, pearling, polishing and grading. 

The cleaning process removes all extraneous matter, such as "dead" grains, stones and stalks. For certain varieties it is necessary to parboil (steep) the cleaned rice in hot water for a time to facilitate removal of the hull and improve the keeping quality of the grain. This process also improves the thiamine content of the grain. There are several methods of removing the hull. Hulled rice is commonly called brown rice. After hulling, the germ and outer bran are removed in a set of huller reels and pearling cones in which the waxy cuticle is scoured off by the friction between the high-speed abrasive cone and its casing. The resultant bran meal is propelled through meshes of wirecloth and collected. The milling space between the cone and the casing is adjustable so that the milling rate can be varied by raising or lowering the cone. In most mills the rice passes through several cones, each with a higher milling rate. The brans from the different settings are usually mixed into one product. For a finer appearance, rice from the pearler is passed through polishers. These machines are similar to pearling cones except that they contain a drum covered with strops of hide rather than an abrasive cone. In this process a part of the starchy kernel (endosperm) is removed. If inner bran layers are included, the product is called fine bran, or pollard. The mixture of whole and broken rice from the polishers is separated in sieves and then remixed in proportions corresponding to the standard at which the rice is to be sold. The percentage of by- products depends on milling rate, type of rice and other factors. The following figures give an approximate idea of the proportions: hulls, 20%; bran, 10%; polishings, 3%; broken rice, 1-17%; polished rice, 50-66%. 

USES. 

ROUGH RICE (paddy or padi). Rice grains in their hulls are very hard and abrasive and must therefore be ground before they are used as animal feed. They are seldom used owing to their high cost. They have been used, however, to replace maize in cattle and pig rations without ill effects, although feed conversion was somewhat depressed in all cases. For pigs, rough rice can be used to best advantage as a replacement for not more than 50% of the maize in the ration. For laying hens, rough rice gives good results when it constitutes 20-30% of the diet. The feeding of mouldy rice should be avoided. 

BROWN RICE (cargo rice). Dehulled rice that retains the bran coating is sometimes used as feed. Usually ground and sold as "rice meal", it can be fed to all types of animals; it is superior to rough rice as it contains less fibre and silica, and it is richer in protein and vitamins than polished rice. 

BROKEN RICE (chits, brewer's rice) and polished rice (milled rice). The broken rice separated out after the polishing stage has the same chemical composition as polished rice. There is seldom any surplus of broken rice available for feeding, as much of it is remixed with the whole grains and sold as low-grade rice. It is also sold to the brewing industry for mixing with barley. In some countries it is used for the production of arrak or as the raw material for rice flour. 

Broken rice is a palatable, energy-rich and easily used feed. It is used for all classes of livestock, but its high energy value and low fibre content make it especially valuable in rations for growing chickens. Polished rice is seldom used as animal feed because of its high price, but it can be fed in the same way as broken rice. 

RICE HULLS (husks, chaff). Rice hulls are used in some countries for poultry litter that can later be fed to ruminants (see feed information summary I21). Numerous publications on uses of rice hulls attest to the many attempts to solve the problem of disposing of this by-product. It can be used in animal feeding in the following ways: 

1. As raw rice hulls. Low-quality roughages like ground rice hulls can be included in small amounts (up to 15%) in high-concentrate diets for feedlot cattle to help furnish bulk, stimulate appetite and decrease incidence of liver abscesses. In areas with a shortage of roughage, ground rice hulls can be used in place of straw or advantageously as a partial replacement for it. The addition of ground rice hulls has been found in some cases to increase the feed intake. 

2. As ammoniated rice hulls. A process developed for making livestock feed from hulls includes the addition of monocalcium phosphate, removal of silica, ammoniation under pressure and toasting. Ammoniated rice hulls have been used in proportions of up to 40% of the total ration for sheep, without digestive or mastication problems. 

3. Together with bran and polishings. See the feed information summary for RICE MILL FEED. 

RICE BRAN. The bran fraction is 14-18% oil. This oil can be extracted from the bran to avoid the problem of rancidity during storage caused by the presence of a lipolytic enzyme that becomes active when the bran is separated from the rice and rapidly increases the free fatty acid content. The free fatty acid content of bran from parboiled rice is below 3% immediately after millings but increases at the rate of about 1% per hour. Apart from extraction of the oils the rancidity process can be delayed by heating or drying immediately after milling. Heating to 100 C for four or five minutes with live steam is sufficient to retard the increase in free fatty acids. The rice bran can also be heated dry if spread out on trays at 200 C for ten minutes. The same effect can be obtained by reducing the moisture content to below 4%. Most chemical inhibitors are ineffective. 

Rice bran is the most important rice by-product. It is a good source of B-vitamins and is fairly palatable to farm animals. The oil has a marked softening effect on body fat and on the butterfat in milk. With attention to the oil content, rice bran is a valuable feed for all classes of livestock. The maximum amount advisable for cattle is about 40% of the total ration. For pigs, rice bran should not exceed 30-40% of the total ration to avoid soft pork; in the final weeks of fattening, lower levels must be used. Up to 25% can be included in poultry rations; double that amount has been used successfully in experiments. Rice bran that has not been defatted is a useful binder in mixed feeds. De-oiled rice bran can be used at higher levels than ordinary rice bran. Rice bran is often adulterated with rice hulls, as it should have a crude fibre content of 10-15%. The product containing large amounts of hulls should be sold under the name "rice mill feed", which is much inferior to rice bran. 

RICE POLISHINGS. Polishings present the same storage problems as rice bran. Polishings have a wider use than rice bran because of their lower fibre content. They can be used in poultry and pig rations, but only in small amounts for piglets as they may cause scour. Like rice bran, polishings should be limited in the diet during the final weeks of fattening to avoid oily carcasses. Up to 5 kg per day have been fed to dairy cows without harmful effects or changes in production. 

RICE POLLARDS. This mixture of bran and polishing is used in the same way and with the same limitations as rice bran. 

RICE MILL FEED. A mixture of all the by-products obtained in the milling of rice, it contains approximately 60% hulls; 35% bran and 5% polishings. The offal obtained from one-stage mills is of similar composition and is often erroneously called "rice bran". Production of rice mill feed in multistage mills is somewhat cheaper than separate production of the ingredients. The suitability of rice mill feed for animals has been well established. In countries where the use of rice hulls as animal feed is legally allowed, up to 75% of the hay can be replaced by rice mill feed with good results.