Copper Vineyard Treatments May Alter Wine Aroma

Study Reveals Hidden Cost of Copper in Vineyards

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For as long as humans have cultivated grapes, the battle against vineyard pests has raged on. In recent history, one of the most common solutions has been the application of copper-based compounds. These compounds, hailed for their ability to combat diseases like downy mildew, have become a staple in European vineyards. However, a new study published in Scientific Reports this May titled "Copper-based grape pest management has impacted wine aroma" by Irene De Guidi, Virginie Galeote, Bruno Blondin, and Jean-Luc Legras, suggests that this practice might come with a hidden cost: it could be altering the aroma profile of our wines.

A Whiff of Sulfur

The aroma of wine, a complex symphony of scents, can be disrupted by even small changes. At the heart of this study is hydrogen sulfide (H2S), a compound notorious for its rotten egg smell. H2S is produced during fermentation by the yeast Saccharomyces cerevisiae. When vineyards are treated with copper, the yeast adapt by amplifying a specific gene, CUP1, which helps them detoxify copper. But here's the catch: this adaptation can lead to increased H2S production, which, as you might guess, is bad news for wine lovers.

The researchers examined 51 strains of S. cerevisiae from three ecological niches: wine, the film-forming flor (used in sherry), and oak trees. Their findings were striking. Wine yeast strains produced significantly more H2S when exposed to sulfite compared to flor and oak strains. This variability in H2S production was linked to the copper levels in the grape must (the crushed grape juice before fermentation).

While copper helps in pest control, it also indirectly boosts H2S production. Industrial wine strains like VL1 and LMD17, exposed to increasing copper concentrations, churned out more H2S. This relationship was particularly evident in strains with a moderate number of CUP1 gene copies (up to 10). Beyond this point, additional gene copies actually reduced H2S production, a curious non-linear relationship that underscores the complexity of yeast genetics.

The Sulfite Factor

Sulfites, commonly added during winemaking for their antimicrobial and antioxidant properties, also play a role in this aromatic puzzle. The study found that sulfites can enhance copper resistance across all tested strains, even those with high CUP1 amplification. However, this boost in resistance comes at a cost: increased H2S production. It appears that external sulfite might overwhelm the yeast's sulfur metabolism, leading to more H2S and more sulfur-rich amino acids necessary for the production of Cup1p, a protein that helps detoxify copper.

The implications of these findings are significant. The long-term use of copper in vineyards has driven yeast to adapt in ways that can harm wine quality. As winemakers seek to balance pest control with maintaining the delicate aroma profile of their wines, this research highlights the importance of considering the genetic background of yeast strains. By selecting strains with optimal CUP1 gene configurations, winemakers might minimize H2S production and preserve the sensory qualities of their wines.

This study was funded by the Horizon 2020 research and innovation program of the European Union and France's National Research Agency, pointing to the broader interest and support for understanding and improving viticultural practices. As the wine industry continues to evolve, integrating such scientific insights could pave the way for more sustainable and aroma-friendly pest management strategies.

So, the next time you enjoy a glass of your favorite vintage, take a moment to appreciate not just the flavors and aromas but the intricate dance of science and nature that made it possible. After all, every sip of wine is a testament to centuries of agricultural practice, ongoing research, and the ever-adapting world of yeast.

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