Appearance of poor-fermenting variants in brewing yeast culture.

A class of yeast variants appears after cultivation of a bottom-fermenting brewing yeast strain, IFO2003. Although IFO2003 fails to grow well above 33 degreesC, the variants can grow up to 34 degreesC. Temperature-resistance and an acquired phenotype of maltose poor-fermentation ability are strictly correlated in the bottom-fermenting brewing yeast, enabling us to develop easy estimation of the fermentation ability of the variants.