Oxygen has been reported to stimulate yeast growth and fer- mentation, and the improvement of ethanol yield by aeration is more significant at high dilution rates (Ryu et al., 1984). In addition, our previous study showed that aeration could also facilitate floc- culability (Kida et al., 1989). Therefore, the effects of aeration rate were studied. As shown in Figs. 2c and 3c,