Hayawaki (premature onset of fermentation in the yeast starter)

Hayawaki refers to the timing at which yeast begins fermenting during sake brewing. It is seen especially in kimoto-type and sokujo-type shubo (yeast starter), and describes yeast starting to ferment actively even though the saccharification of the steamed rice and the formation of acid have not yet progressed sufficiently. When hayawaki occurs, fermentation may become uneven or the flavor may be affected, so brewers need to be careful. Because fermentation proceeds quickly, the character and taste of the sake may end up changing.