A recent study by INRAE and the Institute Agro has uncovered that copper-based treatments used in vineyards, such as Bordeaux mixture, can lead to an undesirable rotten egg taste in wine. The research, published in Scientific Reports, reveals that yeast strains resistant to copper produce excessive hydrogen sulfide (H2S), a compound responsible for this off-putting odor.
Study Insights
The study examined 51 yeast strains, finding that those with a higher number of copies of the gene CUP1, which confers copper resistance, produced less H2S. Strains with more than 10 copies of this gene showed a significant reduction or even elimination of H2S production.
Yeast and Winemaking
Saccharomyces cerevisiae, the yeast used in winemaking, plays a critical role in fermenting grape must into alcohol and synthesizing sulfur amino acids necessary for its growth. However, this process also produces H2S, which can spoil the wine’s flavor.
Researchers explored how traditional vineyard practices, such as using Bordeaux mixture and adding sulfites during winemaking, affect H2S production. Bordeaux mixture, a copper-based antifungal treatment, has been used for over a century and is allowed in organic farming. Sulfiting, the addition of sulfites, helps preserve wine quality.
Findings and Implications
The study found that wine-derived Saccharomyces cerevisiae strains, exposed to copper from Bordeaux mixture, had increased H2S production compared to strains from oak bark or wine film. The addition of sulfites further amplified H2S synthesis.
Copper resistance in these yeasts, due to the multiplication of the CUP1 gene, leads to overproduction of H2S during fermentation. This excessive H2S production can significantly degrade wine quality. The research demonstrated that exposing yeasts to copper increased H2S production and that strains with more than 20 copies of the CUP1 gene had decreased H2S levels.
Future Directions
These findings suggest a potential avenue for improving wine quality by selecting yeast strains with higher resistance to copper, thus reducing H2S production. Understanding yeast resistance and adaptation mechanisms is essential for optimizing winemaking practices, particularly in the face of evolving health and climate challenges.
This study highlights the need for ongoing research into yeast strains to mitigate the negative impacts of copper-based vineyard treatments on wine quality.
