Atsubuta (thick rice-grain cap on the fermenting mash)

Atsubuta (厚蓋) refers to a condition in the fermentation of sake moromi (fermentation mash) in which a thick layer of rice grains floats on the surface of the mash. It appears as saccharification and fermentation progress, particularly when yeast activity is at its peak. Atsubuta is often compared with other foam stages (such as bozu, chirimen awa, and iibuta), and it is important as a way of observing how the shape and appearance of the foam change as fermentation advances. It is also regarded as one indicator of the health of the moromi, and brewers watch it especially closely during sake making.