Koji-buta (koji trays)

Koji-buta (麹蓋) are an important tool used in the koji-making stage of sake brewing. They are shallow boxes made mainly of cedar, used to propagate koji mold (koji-kin) on steamed rice. The boxes help with controlling the temperature of the koji, but because they require considerable labor, they are most often used in the production of premium sake. They are used when the buta-koji method (蓋麹法), a specific koji-making technique, is employed, and each tray can hold about 1.5 to 2 kg of steamed rice. Using koji-buta helps produce higher-quality koji, which in turn enhances the flavor and aroma of the finished sake.