3.3. Continuous ethanol fermentation of thick juice
The continuous ethanol fermentation of thick juice was carried
out by two-stage fermentation at 30 C. As shown in Fig. 6A,
ethanol concentration in R1 stabilized at (59.8 ± 1.6) g L1. The
yeast number and their viability were relatively constant (Fig. 6B).
However, R2 did not perform as expected. Whenever the ethanol
concentration in R2 reached 80 g L1, decrease trends in ethanol
concentration subsequently followed (Fig. 6A), and the yeast
number was 109 cm3, with 50% viable (Fig. 6B). In our previous
study, it has been estimated that the number of viable yeast must
be retained at 1.3 109 cm3 in the reactor to achieve an ethanol
concentration of 85 g L1 [22]. Moreover, the cell activity as reflected in the respiration rate as CO2 was very low in R2, being