Koji muro (koji room)

A koji muro (麹室, koji room) is a dedicated room for producing koji, and it plays an important role in sake brewing in particular. The room is designed to maintain the temperature and humidity best suited to the growth of koji mold. In general, koji rooms are built mainly with cedar boards, giving a structure with high heat retention that is resistant to condensation. A koji room usually has two sections (groups), each managed so that it can hold a stable temperature of roughly 30°C to 45°C. Because humidity is easy to adjust, the room provides an environment that encourages the growth of koji mold and the making of high-quality koji. In addition, heaters and ventilation equipment are installed to maintain the temperature, so that suitable conditions are kept. In this way, the koji room is an indispensable facility in sake making.