High ethanol titer in fermentation broth is crucially important
for reducing the energy demand of the consequent distillation step
(Galbe et al., 2007). When cellulosic ethanol fermentation is conducted
using lignocellulose feedstock, the simultaneous saccharification
and fermentation (SSF) technology is frequently used to
lessen the strong inhibition of high sugar concentration on
cellulase enzyme catalyzed cellulose hydrolysis. During SSF, high
solid feedstock content is certainly required to reach the high ethanol
titer. Consequently, two difficulties emerged in such a high
solids content fermentation: the poor mixing of the solid feedstock
majority with the liquid minority of cellulase enzyme solution and
fermenting seeds broth, as well as the accumulation of inhibitory
compounds with the increased pretreated solids content.