Production of fuel ethanol from rye and triticale by very-high-gravity (VHG) fermentation

Very-high-gravity (VHG) rye and triticale mashes, containing about 28.5 g dissolved solids/100 mL of mash supernatant, were prepared by adjusting water:grain ratios to 2:1. Because of high viscosity, which develops during mashing, it was necessary to pretreat ground rye-water slurries with viscosity-reducing enzymes. There were no viscosity problems during the preparation of triticale mashes. Fermentations were conducted at 20°C, with and without 16 mM urea as a nitrogenous supplement. All fermentations were completed within 120–144 h. Supplementation with urea shortened the times required for completion of fermentation by 33% for triticale and by 40% for rye. The fermentation efficiencies for both grains ranged between 90 and 93%. These values are comparable to those reported for wheat, implying competitiveness of rye and triticale as fermentation feedstocks to replace wheat. The final ethanol yields were 409 L for rye and 417–435 L for triticale/t (dry basis). For a given size of fermentation vessel, 33% more grain was used in the VHG fermentation process than in normal gravity fermentation. This resulted in a 35–56% increase in ethanol concentration in the beer, when fermentors were filled to a constant volume. The corresponding reduction in water use by about one-third would result in savings in energy consumption in mash heating, mash cooling, and ethanol distillation. Fermentation efficiencies and final ethanol yields obtained per unit weight of grain fermented were not significantly different from the normal gravity fermentations.