Ethanol fermentation of very high gravity (VHG) maize mashes by Saccharomyces cerevisiae with spent brewer's yeast supplementation

• Ethanol fermentation of VHG maize mashes with spent brewer's yeast supplementation was conducted.
• Supplementation led to decrease in ethanol production rate.
• Mashes supplementation shorten the fermentation time.
• Spent yeast supplementation increases ethanol yield.

The subject of this research project was ethanol productivity from very high gravity maize mashes supplemented with spent brewer's yeast as a nutrient source. Batch fermentation of maize mashes (360 g of maize per kilogram of mash) supplemented with 30 g of spent brewer's yeast's wet biomass, dried spent brewer's yeast and yeast extract per kilogram of mash was conducted for 96 h at 30 °C. In all supplemented mashes higher ethanol production rate was observed in comparison to the control sample, especially in the initial stages of fermentation. After 96 h fermentation the ethanol concentration ranged from 120.95 to 142.34 g dm−3 in supplemented mashes (120.74 g dm−3 in the control sample) which corresponded with practical ethanol yields of 78.05–91.85% (77.91% in the control sample). It was also important that maximum ethanol yield in supplemented mashes was achieved after ca. 48 h and 72 h of fermentation while in the control sample ethanol production continued until the end of the process.