Winemakers have the ability to influence a range of components during the winemaking process. Managing wine pH and remedial treatments such as Cu2+ fining, are two of these variables that can be controlled post-fermentation before bottling, helping winemakers to instill their unique style and signature to wines. The role of Cu2+ in the formation of H2S has been well established, however, the synergistic effect of wine pH and Cu2+ addition on the formation of volatile sulfur compounds (VSCs) associated with ‘reductive’ aromas in wines has not yet been studied. Four VSC compounds were significantly influenced by pH effects, with lower wine pH associated with decreased H2S, MeSH, DMS, and CS2 concentrations in both Chardonnay and Shiraz wines. Treating wines with Cu2+ resulted in significantly increased H2S (Figure 1), however, at lower wine pH the total produced H2S concentration was significantly decreased. This suggests the availability of Cu2+ to catalyze the formation of H2S was inhibited by lowering the pH of the wines. The interaction between H2S and variable pH concentrations on Cu2+-complex particle sizes was subsequently studied in a model wine matrix using nanoparticle tracking analysis. It was found that different wine pH levels as well as H2S addition significantly impacts the particle size and concentrations. This suggest that the pH of the wine affects the type of Cu2+-complexes produced which may subsequently impact on the reactivity of Cu2+ and its ability to interact with wine compounds and be involved in the catalytic formation of VSCs. These results confirm that formation of VSCs post-bottling is regulated by a complex range of variables. Some, such as pH and Cu2+ treatment, are within winemakers’ ability to manipulate to reduce the overall impact of VSCs on wine aroma.

Synergistic effects of copper and pH - wine making variables that significantly impact reductive aromas in wines

251st National Meeting (2016)

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