Fukure (swelling of the yeast starter)

Fukure refers to the stage, after the shubo (yeast starter) has been prepared, when the yeast begins to multiply. As the yeast converts sugar into alcohol, it gives off carbon dioxide gas, which forms foam on the surface of the shubo and makes it swell. This swelling can be observed. The state of the fukure shows that fermentation is progressing well, and it is regarded as an important indicator in sake brewing. During the fukure period the shubo is highly active, and it is a crucial time that influences the aroma and flavor of the finished sake.