Abstract
Rice milling technology has a large influence on sake brewing as well as edible rice quality. The purpose of rice milling for edible rice is to remove the embryo, pericarp, seed coat and aleurone layers. A part of the endosperm is also polished for sake brewing to improve flavor and color. Since large amounts of lipids and minerals are contained on the surface layer of brown rice, most of them are removed in the early stage of rice milling. On the other hand, although the amount of protein is higher on the surface layer, it also is present in the endosperm, so the decrease in protein due to rice milling is only partial. Therefore, in the production of ginjo and daiginjo, the protein is reduced as much as possible by polishing to a ricepolishing ratio of 60% or 50% or less.
In recent years, a new type of brewing milling machine was developed, which has rolls in which abrasive grains of cubic boron nitride are electrodeposited on base metals as an abrasive. By selecting rolls with a small abrasive grain size, it has become possible to get flat polished rice that can reduced protein efficiently without significantly taking a long rice milling time. If flat polished rice or original-shaped polished rice is selected according to rice variety, shape of shimpaku, and the rice-polishing ratio, it is possible to mill rice that can efficiently reduce protein without problems in the remaining embryos using a low ricepolishing ratio and with generation of crushed grains during a high rice-polishing ratio. Therefore, we believe this will contribute to higher quality sake brewing.
