Regardless of the corn material used, the control gave significantly
lower lmax;CO2 than any other skim treatments (Table 1).
The interaction between skim replacement level and corn particle
size was insignificant (p = 0.88). When examining the fermentation
rates from each corn material, for coarsely ground corn, the
averaged lmax;CO2 of all the skim replacement treatments was
21 mL/min, which was 10% higher than the rate of the control;
for corn flour, the averaged lmax;CO2 of all the skim replacement treatments was 23 mL/min, about 28% higher than that of the control;
and for finely ground corn, the averaged lmax;CO2 of all the
skim replacement treatments was 24 mL/min, 10% higher than that
of the control. Compared with the control the greatest rate increase
was from corn flour. Since these experiments were designed with a
fixed water-to-solids ratio of 2.4, the effects of solids concentration
of initial slurry on liquefaction and the following saccharification
and fermentation were minimal when the same corn material
was used. The particle size of skim solids was greatly different from
ground corn, thus, the difference might affect the mash viscosity
and consequently influence the performance of enzymatic hydrolysis
and yeast fermentation when different proportions of skim
were added to the fermentation media. The results showing that
the fermentation rate-promoting effect of soy skim were consistent
for corn materials having various particle sizes removed such
uncertainty even though the ethanol industry will not likely use
such finely ground corn in the actual production due to increased
energy input. The increase of CO2 production rate as affected by
the skim addition resulted in fermentations completed in 5 to
7 h shorter time than for the control.