Molasses used as a substrate in fermentation because it has fairly high sugar content, so it could meet the needs of
carbon source required by yeast during metabolism. The reducing sugar concentration at 0 hour incubation time by
New Aule Alcohol Yeast and New Aule Baker’s Yeast under both fermentation condition were approximately 300
g/L. Throughout fermentation, reducing sugar were well used by both yeast indicated by the increase in the number
of yeast population and ethanol produced. A sharp drop of reducing sugar concentration during 36 hours incubation
time occured and then were slowly going down until 72 hours incubation time for both yeasts. The reducing sugar
concentration of both yeast in the end of incubation time decreased more than 50% until 36 hours of incubation
time. Buglass (2011) stated that 50% sugar availabilities in substrate were used by yeast during logarithmic phase.
Hence, the reducing sugar consumed by both yeast were high during the phase. The reducing sugar consumed by
New Aule Alcohol Yeast and New Aule Baker’s Yeast under non-aerated culture at 36 hours of incubation time
were 196.274 g/L and 237.583 g/L, respectively. Under aerated culture, reducing sugar consumption by both yeast
were tend to be higher compare to non-aerated culture, with reducing sugar consumption at 221.880 g/L and
246,649 g/L, indicated that aeration led to increasement in sugar consumption of both yeast. Yan et al. (2009) stated
that oxygen availability in the earlier fermentation used by yeast for respiration, so that it could accelerate yeast
growth and agitation could homogenize fermentation media, so nutrition and oxygen supply added were well
utilized by yeast. Correlated with Rodmui et al. (2008), stated that controlled aeration during lag and log phase
could incerase sugar consumption in substrate which could accelerated lag phase and increasement in biomass
production.
Saccharomyces cerevisiae produced metabolite such as alcohol dehydrogenase enzyme which can convert sugars
to ethanol. During fermentation, sugars content in media used by yeast were not only for growth and proliferation,
but also to produce ethanol. Glucose in substrate will be converted to pyruvic acid through glycolysis. The pyruvic
acid then converted to acetaldehyde and CO2, the acetaldehyde further will be converted to ethanol by alcohol
dehydrogenase enzyme (Buglass, 2011). Based on Fig.1 showed that the increase in ethanol concentration by both
yeast occured until 36 hours of incubation time. The maximum ethanol concentration produced by New Aule
Alcohol Yeast and New Aule Baker’s Yeast under non-aerated culture were significantly different, with result at
74.80 g/L and 102.85 g/L, respectively. Meanwhile, under aerated culture the ethanol produced by New Aule
Alcohol Yeast was not significantly different compare to its non-aerated culture showed that there was no significant
effect given aeration in culture media during 36 hours fermentation, but different at 48 hours fermentation led to an