Alcoholic fermentation with high sugar and cell concentration at moderate temperatures using flocculant yeasts

This paper studied bioethanol production at very high gravity (VHG) conditions using flocculent Saccharomyces cerevisiae, evaluating the response yield, ethanol concentration, productivity, and residual sugar through a central composite design (CCD). This CCD was evaluated at 12 and 24 h fermentation times. In the CCD evaluated for 12 h of fermentation, the best condition for alcoholic fermentation was 27 °C, 260 g/L substrate concentration and a 30% v/v cell concentration; a maximum overall desirability of 0.937 was achieved. For CCD at 24 h of fermentation, the best condition was 27 °C, 300 g/L substrate concentration, and a 26% v/v cell concentration. The desirability achieved was 0.811. These conditions allowed us to verify, experimentally, that the CCD models described the fermentation behavior well. VHG alcoholic fermentation in fed-batch with the reuse of cells without chemical treatment was performed using the optimum conditions obtained from the desirability function (27 °C, 300 g/L, 26% v/v). This resulted in favorable alcohol content 132.90 g/L in comparison to the conventional fermentation process.