2 BULLETIN 570, U. S. DEPARTMENT OF AGRICULTURE. 



The rice grain as it is received at the mill from the farm thrasher 

 is contained in a hard, siliceous hull which incloses the edible kernel. 

 This hull is covered with small needlelike points very high in silica 

 content. Directly beneath the hull, but separate from it and at- 

 tached firmly to the endosperm or starchy body of the kernel itself, 

 is a light-brown bran coat. The microscope reveals seven distinct 

 layers of bran. At one end of the hulled kernel the germ or embryo 

 is distinctly visible. The milling process normally removes the 

 germ, six of the bran layers and a part of the seventh or aleurone 

 layer, and leaves only the starchy part of the kernel surrounded by 

 a portion of the last layer. The aleurone cells are very rich in pro- 

 tein and only about 10 per cent of the protein of the hulled rice is 

 removed by milling. Most of the oil, however, is contained in the 

 germ, and since all of the germ goes into the bran about 85 per cent 

 of the oil content of the kernel is removed. 



DESCRIPTION OF THE MILLING PROCESS. 



The rice as it comes to the mill is termed ''rough rice" and usually 

 is received in sacks which ordinarily contain from 175 to 210 pounds 

 each, the average being about 190 pounds. The trade, however, 

 usually considers that 162 pounds constitute a "barrel." From 

 the mill warehouse the rough rice is elevated to the top floor of the 

 mill, where the cleaning process begins. The rough rice goes over a 

 machine called a " scalper," which removes the sticks, stones, and 

 other coarse material by screens and removes the dust and fine ma- 

 terial by suction. From the scalper the rice goes to the "clipper," 

 which removes the long beard and stems; and from the clipper to 

 a "monitor," which by suction removes light or blighted grains of 

 rice. The product now might be termed "cleaned rough rice," and 

 upon this product the milling process proper is conducted. 



MILLING MACHINERY. 



Hulling stones. — The milling process may be divided into three 

 parts, each of which removes a different portion of the rice and pro- 

 duces a distinct by-product. The first step is the removal of the 

 hull; the second, the removal of the outer bran; and the third, the 

 removal of the inner bran. The cleaned rough rice goes to a pair 

 of milling stones, similar to the old-time flour-mill buhrstones. 

 These stones, the top one of which usually revolves, are set some 

 distance apart, so that the revolving of the stone causes the grains 

 to assume a somewhat vertical position. In this position a pressure 

 is exerted on the ends of the grain, which cracks or splits the hull, 

 allowing the kernel to drop out. Care is taken to set the stones a 

 sufficient distance apart so that there will be as little breaking of the 



