Tsumikae (restacking of koji trays)

Tsumikae (積替え) is an operation carried out in sake production, particularly during koji making with the koji-buta (wooden tray) method. While the dried koji is in stacked trays, the positions of the koji trays are changed in order to even out the temperature differences between them. Specifically, between the mori and naka shigoto stages, and between the shimai shigoto and dekoji stages, the koji is not stirred. Instead, the trays are simply swapped in position, top and bottom, front and back, and left and right, to balance the fermentation environment inside the koji. This operation reduces temperature differences and encourages even fermentation, which in turn contributes to producing high-quality sake.