FERMENTATION OF VERY HIGH GRAVITY WHEAT MASH PREPARED USING FRESH YEAST AUTOLYSATE

The use of autolysed spent yeast cells as a source of extra free amino nitrogen (FAN) resulted in significantly accelerated rates of sugar utilization and ethanol production under very high gravity (VHG) fermentation conditions. These rates were comparable to those obtained in urea-supplemented fermentations. Analysis of thin stillage backset from grain-based fuel ethanol plants indicated that backset contains insufficient FAN to produce maximum rates of fermentation under VHG conditions. Use of thin stillage is therefore more important as a method to conserve water usage and pollution costs than as a source of nutrients. Our results suggest that a yeast autolysate prepared from harvested spent yeast or waste yeast slurry acquired from a brewery and used in conjunction with backset may be a feasible alternative to improve industrial process economy in normal gravity and in VHG fuel alcohol fermentations.