By Chandré Davey

Introduction

Some wines develop a strange “mousy” flavour, described as basmati rice, mouse urine, or sausage skin. You can only taste it because the compounds causing it aren’t very volatile. Lactic acid bacteria and the yeast Brettanomyces, both known troublemakers in wine, can produce these off-flavours. A new study by Moulis et al. (2024)explored how combinations of these microorganisms, rather than single species, contribute to the defect, bringing winemakers a step closer to understanding and preventing the dreaded “mousiness.”

Results

The 2024 study by Moulis et al. explored whether the common winemaking yeast Saccharomyces cerevisiae affects the “mousy” aromas produced by Brettanomyces bruxellensis. Using advanced chemical analysis (SBSE-GC-MS), the team compared the presence of key compounds responsible for the defect. Previous research shows that Brettanomyces bruxellensis doesn’t produce the compound APY, even when Saccharomyces cerevisiae is present. However, all tested Brettanomyces strains, alone or combined with Saccharomyces, were able to produce the other two “mousy” compounds, ATHP and ETHP. When Brettanomyces bruxellensis and Saccharomyces cerevisiae are combined, most of the changes in “mousy” compounds come from Brettanomyces, accounting for 88% of ATHP and 62% of ETHP levels. The common winemaking yeast Saccharomyces plays a smaller role. Different Saccharomyces cerevisiae strains produce varying amounts of acetaldehyde, a key precursor to the “mousy” compounds.

Conclusion

The study shows that Saccharomyces cerevisiae and Brettanomyces bruxellensis interact in ways that can influence the development of “mousy” aromas. Even yeast strains previously thought harmless might affect how other microbes produce off-flavours. This is the first study to explore these microbial interactions rather than looking at single species alone. While the findings shed new light on fermentation dynamics, more research is needed to see how they could impact winemaking practices and quality control.

Reference

Pierre Moulis, Cécile Miot-Sertier, Céline Franc, Laurent Riquier, Beata Beisert, Stéphanie Marchand, Gilles de Revel, Doris Rauhut, Patricia Ballestra. Does Saccharomyces cerevisiae play a supporting role in mousy off-flavours production? IVEShttps://doi.org/10.20870/IVES-TR.2025.9206