(0.6 ± 0.1) mm3 min1, when the ethanol concentration reached 80 g L1, which was significantly lower than that of (5.1 ± 0.1) mm3 min1 in R1, where the ethanol concentration was approximately 60 g L1 (Fig. 7). Since there was no increasing trend in lactic acid concentration or acetic acid concentration (Fig. 6C), the decrease in ethanol concentration and yeast cell viability should not be caused by bacterial contamination. Therefore, it can be concluded that the yeast cells suffered from considerable stress at the high ethanol concentration, resulting in a decrease of cell growth and activity, thereby causing a decrease in ethanol concentration [6].