Foam (Awa)

Foam (awa) is an important element in the fermentation process of sake. It is produced mainly when yeast converts sugars into alcohol and carbon dioxide. This carbon dioxide dissolves into the liquid and appears on the surface as foam. How the foam forms and how long it lasts vary with the condition of the fermentation, the temperature, and the type of yeast used, and are influenced by the fermentation environment of the shubo (yeast starter) and the moromi (fermentation mash). Foam also contributes to the taste and aroma of sake, and its effect is especially noticeable in sparkling sake. Because the character of the foam changes as fermentation progresses, observing it is an important indicator in sake brewing.