Molasses was collected directly with 20–30 Brix. The concentration
was adjusted to 30 Brix, when necessary, by the addition
of concentrated molasses (80 Brix), in an agitated tank of 5 m3. Fermentations
were conducted as fed-batches. Biomass was diluted in
water in an agitated tank and transferred to one pair of fermentation
tanks. Air was injected at 1 VVM to allow biomass multiplication
and molasses was fed at the flow rate of 2 m3/h in each tank for
4 h, until tanks were half-filled. Then, half of the content of each
tank was transferred to a pair of subsequent tanks and the procedure
for biomass multiplication was repeated. The first pair of tanks
was fed again with molasses at 4 m3/h, until tanks were filled to 80%
of their capacities, and fermentation was conducted, with no aeration,
to the end of CO2 liberation. This procedure was repeated for
the other pairs of tanks. Dispersant agent was added at the beginning
of feeding and antifoam was used to break the formed foam
after feeding. Temperature control (at 30 C) and agitation were assured
by circulation of the broth through plate heat exchangers.
When fermentation was finished, biomass was separated by
continuous centrifugation, the yeast cream containing around
60% solids was treated with acid (H2SO4 to pH 2.2 for 2 h), in order
to avoid flocculation and inactivate the weak cells, in a 5.5 m3 agitated
tank, and then transferred to the fermentation tanks to be
used as inoculum. Biomass concentration at the beginning of fermentation
was adjusted to at least 3 108 viable cells per mL,
the inoculum volume being around 30% of the total fermentation
volume. The wine was distilled for ethanol recovery.
Molasses was collected directly with 20–30 Brix. The concentrationwas adjusted to 30 Brix, when necessary, by the additionof concentrated molasses (80 Brix), in an agitated tank of 5 m3. Fermentationswere conducted as fed-batches. Biomass was diluted inwater in an agitated tank and transferred to one pair of fermentationtanks. Air was injected at 1 VVM to allow biomass multiplicationand molasses was fed at the flow rate of 2 m3/h in each tank for4 h, until tanks were half-filled. Then, half of the content of eachtank was transferred to a pair of subsequent tanks and the procedurefor biomass multiplication was repeated. The first pair of tankswas fed again with molasses at 4 m3/h, until tanks were filled to 80%of their capacities, and fermentation was conducted, with no aeration,to the end of CO2 liberation. This procedure was repeated forthe other pairs of tanks. Dispersant agent was added at the beginningof feeding and antifoam was used to break the formed foamafter feeding. Temperature control (at 30 C) and agitation were assuredby circulation of the broth through plate heat exchangers.When fermentation was finished, biomass was separated bycontinuous centrifugation, the yeast cream containing around60% solids was treated with acid (H2SO4 to pH 2.2 for 2 h), in orderto avoid flocculation and inactivate the weak cells, in a 5.5 m3 agitatedtank, and then transferred to the fermentation tanks to beused as inoculum. Biomass concentration at the beginning of fermentationwas adjusted to at least 3 108 viable cells per mL,the inoculum volume being around 30% of the total fermentationvolume. The wine was distilled for ethanol recovery.
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