Ishu kokuryu (foreign grain in brewing rice)

Ishu kokuryu (foreign grain) refers to grains other than rice that are mixed in with brown rice intended for sake brewing. Specific examples include unhulled rice (paddy husks) and barley. These foreign grains can affect the quality of the sake, and in the sake brewing process they are generally removed in order to maintain purity of quality. Because their presence can cause unintended changes in fermentation and flavor, care is needed in sake making.