By purging the nitrogen, about 10% ethanol yield could be increased with higher titer in the condensate. The specific ethanol productivity increased from 0.1670.02 g g1 h1 to 0.1970.01 g g1 h1 , at a dilution rate of 0.075 h1 , when the reactor was purged with nitrogen instead of air. This indicates that the presence of oxygen in the broth affects the ethanol yield