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.