IMPROVED ETHANOL YIELDS THROUGH SUPPLEMENTATION WITH EXCESS ASSIMILABLE NITROGEN

Very high gravity (VHG) worts of 24-degrees Plato supplemented with various amounts of yeast extract (YE) were inoculated at two different levels with a commercial lager strain of Saccharomyces cerevisiae, and the resultant beers and yeast crops were analyzed. Excess assimilable nitrogen did not result in higher viable yeast counts but did lead to increased rates of growth and increased accumulation of cell mass (partly due to higher cellular protein content). Fermentation (ethanol production) rates were significantly enhanced by YE supplementation up to 1.25% w/v, and the maximum ethanol concentrations seen were significantly higher as YE levels were increased (maximum effect at 0.75%), although YE itself was largely unfermentable. Lower ethanol yields in unsupplemented control worts could not be explained by increased carbon diversion to acetaldehyde, glycerol, or glycogen.