Shubo koji (koji for the yeast starter)

Shubo koji (酒母麹) is the koji used in making shubo (yeast starter). Shubo is the liquid base used in the early stage of sake fermentation, in which yeast and koji are combined so that the yeast becomes active. The koji used for shubo is made by steaming rice and adding koji mold, and it serves to promote saccharification. When shubo koji is properly prepared, good-quality yeast is activated, which is an important factor in producing a flavorful sake in the moromi (fermentation mash) that follows.