Fig. 4, which compares the
performance of flasks containing different concentrations of
sulfurous acid. The highest ethanol yield was 7.9 g ethanol per
100 g fresh stalks obtained with 30 mg sulfurous acid per 100 g
sorghum stalks. It is 91% of the theoretic yield, which is 5.3%
higher than the one without reducing agent of H2SO3.
However, higher sulfurous acid concentration resulted in a
lag period of nearly 50 h (not presented). This may be because
of the inhibitory effects of sulfurous acid on yeast cells. At the
same time, little ethanol was produced in the flask with
sulfurous acid concentration of 50 mg/100 g sorghum.