Fuel alcohol production: appraisal of nitrogenous yeast foods for very high gravity wheat mash fermentation

Abstract

A scientific and economic appraisal of various nitrogen-containing yeast foods usable for very high gravity (VHG) fermentation technology was conducted. VHG wheat mashes containing 350 g dissolved solids per litre were prepared by enzymatic hydrolysis of milled wheat, and then fermented with active dry yeast ( Saccharomyces cerevisiae). Although such wheat mashes were limiting in assimilable nitrogen, they fermented to completion within 9 days at 20°C. However, by adding assimilable forms of nitrogen, fermentation was accelerated. For example, in the presence of 1% (w/w) yeast extract, fermentation was completed in 4 days with a yield of 20·3% (v/v) ethanol. Unfortunately, yeast extract at the required level is too costly for routine use in the fuel alcohol industry. The testing of other nutrient supplements revealed that urea, ammonium ion, and Fermaid K TM compared favourably to yeast extract in stimulating VHG fermentation of wheat mash. Of these, urea is the most economically attractive for the industrial production of fuel alcohol. These results are an important contribution to the industrial assessment of VHG fermentation technology.