Further, the effect of cell mass concentration was observed by increasing the cell mass concentration from 3.570.3 g l1 to 7.171.0 g l1 in the bioreactor at a dilution rate of 0.075 h1 and air purging at a flow rate of 0.5 vvm through the bioreactor, the ethanol concentration in the condensate increased from 37.770.3 g l1 to 44.670.6 g l1 with the almost same ethanol yield (Fig. 2).