seimai

Seimai, or rice polishing, is the process of milling away the bran and germ from rice grains using mechanical mills. The practice serves to produce a refined grain with a higher starch content and a cleaner texture, suitable for cooking white rice or for fermentation in sake production.

The extent of milling is expressed as seimaibuai, the rice polishing ratio, defined as the percentage of the original grain that remains after milling. For instance, a seimaibuai of 60% indicates that 40% of the outer layers have been removed. The seimaibuai is a key quality parameter in many rice-based products, especially sake.

In sake brewing, polishing removes proteins, fats, and other compounds that can influence flavor and aroma during fermentation. More highly polished rice tends to produce lighter, more fragrant products. Sake classifications commonly reference polishing levels, such as ginjo (polished to 60% or less) and daiginjo (50% or less), with some variants like junmai ginjo following the same thresholds.

For everyday rice meant for cooking, milling removes husk and bran to produce white rice. The degree of milling varies by rice variety, tradition, and desired texture, with brown rice representing minimal milling. Commercial mills adjust seimaibuai to balance texture, flavor, and cooking properties.

Seimai became widespread with the adoption of mechanized milling in Japan and later expanded globally through sake production and the rice industry. Today, seimai remains a standard term for rice milling and quality control in many rice-based products.