although the number of yeast did not decrease with decreasing aeration rates, viability decreased significantly from approximately 80% to 40%, when the aeration rate was reduced to ≤0.020 vvm. Viability increased at an aeration rate of 0.005 vvm because of the alleviation of ethanol stress with decrease in ethanol concentration, but decreased again at an aeration rate of 0 vvm (Fig. 2c).