Practical significance of relative assimilable nitrogen requirements of yeast: a preliminary study of fermentation performance and liberation of H₂S

Abstract

Saccharomyces cerevisiae wine yeast strains AWRI 796 and AWRI 835, representing a high and a low nitrogen-requiring strain respectively, were cultured in media of varying nitrogen (ammonium) content. Ammonium utilisation, biomass yield, fermentation progress and the liberation of hydrogen sulfide were monitored. Findings from this study support the original classification of these strains in terms of their relative requirement for nitrogen. Accordingly, when compared with AWRI 835 grown under the same conditions, the high nitrogen-requiring strain, AWRI 796, removed c. 8% more nitrogen from the medium, produced c. 7 to 13% more biomass, failed to complete fermentation in the time frame of the experiment and liberated hydrogen sulfide in greater amounts and/or over longer periods. These findings confirm that measures of relative nitrogen requirement form an extremely useful parameter by which to select strains that are better suited to the problem-free fermentation of musts of low nitrogen content.