Moromi no Jobo (appearance of the fermenting mash)

Moromi no jobo refers to the condition of the foam and the surface of the moromi (fermentation mash) in sake brewing. Moromi is the state in which rice and water are mixed with yeast and koji and left to ferment. As fermentation progresses, various kinds of foam appear on the surface of the moromi, and their appearance changes over time. The first foam to appear is formed by the action of the yeast and is called suji-awa (streak foam). After several days, a light, white foam spreads across the surface; this is called mizu-awa (water foam). After mizu-awa, the foam swells upward into shapes resembling rocks, and is therefore called iwa-awa (rock foam). When the foam rises higher still, it becomes taka-awa (high foam), and the stage in which the foam begins to subside is called ochi-awa (falling foam). After the foam has fallen, light bubbles like soap bubbles remain; these are called tama-awa (bubble foam). Finally, when the foam disappears and the surface of the moromi is exposed, the state is called "ji" (the bare surface). The ji state varies: when nothing is floating on the surface it is called bozu; when a thin, film-like layer of foam floats on it, it is called chirimen-awa or usukawa (thin skin); and when rice-grain-like forms float thickly on the surface, it may be called atsubuta (thick lid) or meshibuta (rice lid). In this way, moromi no jobo is an important indicator in the fermentation process of sake, and by observing how the foam changes, brewers can gauge how fermentation is progressing.