Mizuawa (foam stage in moromi fermentation)

Mizuawa (水泡) refers to one of the fermentation stages observed in the moromi (fermentation mash) of sake. As fermentation progresses, yeast works in parallel with saccharification, and the foam on the surface of the moromi changes over time. It begins with sujiawa (筋泡), and after several days a thin, white, film-like foam spreads across the surface. This state is called mizuawa, a characteristic phenomenon seen as fermentation advances. Mizuawa indicates that the moromi is fermenting actively. The shape of the foam then gradually changes, advancing to iwaawa (岩泡), a foam that rises higher, and then to takaawa (高泡), which rises higher still. In this way, the state of fermentation is observed through the shape and size of the foam, which serves as an important indicator of how far fermentation has progressed. Finally, the foam subsides, leaving soap-bubble-like foam called tamaawa (玉泡), and when the foam disappears, the surface of the moromi reaches a state called ji (地). At this stage, various terms (such as bozu, chirimen awa, and atsubuta) are used depending on the appearance of the moromi surface, describing the characteristics of the fermentation in more detail. Observing mizuawa is a very important part of the sake-making process.