Nururi koji (slimy, sticky koji)

Nururi koji is a condition in which a specific microorganism, Bacillus subtilis (枯草菌, kosokin), multiplies on the surface of the koji, leaving it smooth and sticky. Koji in this state may form a lump, like a dumpling, when squeezed in the hand. Nururi koji is not ideal for sake brewing because the koji mold (Aspergillus oryzae) has not propagated sufficiently. In this state, fermentation tends to be incomplete, and the quality of the sake is often adversely affected. In general, the healthy growth of good-quality koji mold is considered essential to brewing good sake, so a condition like nururi koji is to be avoided. This type of koji is also sometimes called "neba koji" (sticky koji).