Validation of bismuth containing indicator media for predicting H₂S-producing potential of Saccharomyces cerevisiae wine yeasts under enological conditions

Abstract

Hydrogen sulfide (H2S) production by strains of Saccharomyces cerevisiae was compared using bismuth-containing indicator media and fermentations in model grape juice. Discoloration of yeast colonies on indicator media resulting from the production of H2S was essentially independent of nitrogen, sulfite, and glucose levels or the availability of oxygen. Discoloration on bismuth-containing test media did not correlate with H2S production in a complete chemically-defined grape juice medium in which only trace amounts of H2S were produced. By comparison, discoloration on bismuth-containing test media correlated with H2S production developing after nitrogen depletion in a nitrogen-limited liquid medium. It is proposed, therefore, that intensity of discoloration on bismuth-containing indicator media is an indication of the maximum genetically determined sulfite reductase activity for a given strain. While a high sulfite reductase activity does not necessarily predispose a strain to excessive H2S production in complete media, the indicator-media test does appear to predict a high degree of H2S production following nitrogen starvation in liquid media. This screening protocol is therefore valid for assigning the H2S-producing potential of a strain under permissive conditions. In this way, strains identified as high H2S producers can be avoided for the fermentation of low-nitrogen grape juices or where nitrogen supplements can not be made.