Bozu (foam stage with a bare mash surface)

"Bozu" is one of the foam stages seen in the moromi (fermentation mash) of sake as fermentation progresses. It refers to the state in which nothing is floating on the surface of the mash. This state appears among the various changes in foam that occur during fermentation. Specifically, as fermentation advances, the foam passes through several stages, and bozu is the final state in which the foam has almost completely disappeared. In the bozu state, the surface of the liquid becomes flat, making it an important indicator of how fermentation is progressing. Other foam states are also recognized: a state in which a thin skin floats on the surface is called "chirimen awa" (crepe-like foam), and by observing these different foam states, brewers can judge how the sake is developing.