Koji-kin (aspergillus oryzae) is the mold used in shochu production to break down the starches in steamed rice or sweet potatoes into fermentable sugars so that the yeast can then begin their job of converting the sugar into alcohol. Koji-kin is very, very important in producing or affecting the taste of the final shochu.
There are three kinds of koji-kin (mold) for making shochu.
They are kuro (black) koji mold; ki (yellow) koji mold; and shiro (white) koji mold. Each koji mold has a different function to give variation to the final shochu product.