A new assay for the screening of brewing yeasts in their ability to excrete hydrogen sulfide

摘要

Hydrogen sulfide plays a key role in beer quality: I) consumers can easily detect its rotten-egg typical aroma Ⅱ) it can easily bind to allylic alcohols to generate polyfunctional thiols. Polyfunctional thiols are known to have a strong impact on the overall aroma of many fermented foods. In some beers, they could also impart some strong defects like onion-flavours (1). In order to help brewers to avoid unpleasant flavours in beer, a new assay initially proposed to screen other genus of yeasts (2) was used to investigate a large series of S. cerevisiae and S. pastorianus strains issued from our yeast collection. Closed plate flasks containing a zinc-agar layer above the liquid microbial culture are proposed as a trap system where the H_2S can be retained and then quantified by the methylene blue reaction.