Ethanol production from mixtures of sweet sorghum juice and sorghum starch using very high gravity fermentation with urea supplementation

The objective of this research was to enhance the production of ethanol from grain sorghum flour and sweet sorghum juice using very high gravity (VHG) fermentation. Various amounts of grain sorghum flour were combined with different concentrations of sweet sorghum juice to form (≈33 g/100 mL) mashes. Mashes were fermented to produce ethanol with and without urea supplementation via simultaneous saccharification and fermentation process. Based on one-way ANOVA results, all treatment mixtures had a significant effect on ethanol production and efficiency (P < 0.05). It is hypothesized that the combination of inoculation size (109 cells/ml), fermentation temperature (30 °C) and 16 mM urea supplementation had a synergistic effect on ethanol production. Free amino nitrogen consumption dynamics and distiller's dried grains with soluble results suggested that assimilable nitrogen was made available for yeast growth and metabolism. Results showed that 20.25% (v/v) of ethanol and up to 96% fermentation efficiency could be obtained from ≈ 33% (w/v) dissolved solids. Results also showed that the optimum sugar ratio of grain sorghum and sweet sorghum juice (18% sugar) for VHG fermentation is 1-1 (sugar to sugar).