Milling of Rice

Rice wax or rice bran wax is a by-product of the milling of rice. It is commonly used as a coating on food for sale, in chocolate, and as a base for lipstick and other cosmetics. 

Milling of rice is different from that of some of the other cereals in that there is usually no grinding step to produce a powder. Milling involves removal of the hull and bran layers of the rough rice kernel (paddy). Hulled rice (brown rice) is composed of surface bran (6-7% by weight), endosperm (about 90%), and embryo (2-3%). Milling of brown rice uses abrasion and friction between kernels to produce polished or whitened rice, where some 8-10% of the mass (mainly bran) has been removed. 

Pearling barley is a refining process. It removes protein, fiber, minerals, and vitamins. Thus, the decreeise in nutrient content which results from the milling of barley are similar to those resulting from the milling of rice, wheat, corn, and other grains. 

Marshall W. E., Champagne E.T. Evans W.J. (1993) Use of rice milling byproducts (Hulls Bran) to remove metal ions from aqueous solution. J. Environ. Sci. Health A28, 1977-1992. 

A 20-g amount of the milled brown rice or minced vegetable is transferred into a 300-mL Erlenmeyer flask. After 100 mL of 0.2M KOH-acetone (1 9, v/v) have been added to the flask, the mixture is shaken vigorously on a mechanical shaker for 30 min. The homogenate is filtered under vacuum through a funnel fitted with a filter paper, and the residue is rehomogenized with 70 mL of the same solution and filtered again. The filtrates are combined and concentrated to about 40 mL using a vacuum rotary evaporator below 40 °C. 

Collect 1 kg of rice grains and grind with a mill. Collect about 1 kg of rice straw and grind with a grinder. Soil, collected from the top 10-cm surface layer, is homogenized and passed through a 5-mm sieve. 

Brown rice, wheat and bean. Several analytical procedures have been developed for rice grain. In the case of rice straw, finely cut samples are added to water and allowed to stand for 2 h, then extracted with acetone. Unpolished rice grain samples are milled with an ultracentrifuge mill and sieved through a 42-mesh screen prior to extraction. 

Analytical procedure. Homogenization and milling for rice grain and rice straw samples must be carried out in the presence of dry-ice. During evaporation of organic solvents, the temperature of the water bath should be kept at 40 °C or lower. 

Nearly 1.1 million ha of rice were planted in the US in 2012, yielding an average of 8.3 Mg ha-1 for a total production of 9.0 Tg of rice prior to milling, compared to 23 million ha planted with an average yield of 3.1 Mg ha-1 for a total of 62 Tg of wheat production, and over 39 million ha of planted maize with average yields of 7.7 Mg ha-1 for a total production of 274 Tg [11]. 

Mills that process rice may also generate process heat, that can be used for direct heating, steam generation, mechanical power or electrical power. For every five tons of rice milled, one ton of husks with an energy content equivalent to one ton of wood is left as residue. A rice mill in Louisiana has satisfied all its power needs since 1984 from an on-site rice-husk power plant. The plant sells surplus energy to the local utility. 

Rice has big differences in taste between varieties. Therefore, different varieties of rice are blended in the milling plant to provide rice with a desired taste. Since the blending ratio is decided on the basis of sensory evaluation by a few experts, blending can not be conducted automatically. 

The polished white rice that is an important staple food for a large section of the human population is obtained by milling paddy rice. It is first dehulled to yield the following fractions (approximate proportions in parentheses) brown rice (80%) and hulls (20%). The brown rice is then milled to yield rice... 

Table 4.1.29A. Rice bran (IFN 4-03-928). The pericarp or bran layer and germ of the rice, with only such quantity of hull fragments, chipped, broken or brewers rice and calcium carbonate as is unavoidable in the regular milling of edible rice. It must contain not more than 139 g/kg fibre. (From AAFCO, 2005.)...

The vast majority of starch produced in the United States, either for sale as starch or for conversion to other products, is derived by the wet-milling of com. A small amount of starch is also produced by isolation from potatoes or extraction from wheat or rice flour. Current US companies involved in starch production are as follows. 

Milled rice is comprised of head rice, second heads and brewers rice. Unlike most grains, the primary use of rice is its direct consumption as a table food. The two other major uses are in processed foods and to make beer. Head rice is the only rice that is used for table consumption and represents —82% of the milled rice. Broken rice, which is comprised of second heads and brewers rice, is considered to be a byproduct of milling and represents —18% of the milled rice. Broken rice generally has a lower market value than head rice. Due to the relatively high cost of head rice compared with other grains, lower cost by-products of head rice production are preferred for use in processed foods and beer production. In 2004-2005, the USDA estimated that the principle outlets for milled rice in the US included 52% for direct food use,... 

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