Wakitsuki (foaming phenomenon in the yeast starter)

Wakitsuki (湧突き) is one of the phenomena that occur while the shubo (yeast starter) of sake is developing. As the shubo swells, yeast growth and fermentation become more active, and carbon dioxide is produced. This carbon dioxide forms foam on the surface of the shubo, a state known as awamen (foam surface). Wakitsuki is an important indicator of the shubo's condition and how far fermentation has progressed, and it is an essential part of brewing good sake.