Tiziana Nardi_CREA-VE (Italia)

The aim of this work was to verify the potential effect of copper residues on alcoholic fermentation, focusing on Cu2+ concentrations compatible with real ranges of vineyard contamination. In fact, the goal of the trial was to compare different commercial strains of Saccharomyces cerevisiae in order to observe the effect of copper on their metabolism (in terms of: fermentation kinetics, production of free and total SO2 and production of acetaldehyde), rather than to verify at what copper concentration the fermentation goes sluggish or stuck. A second objective was also to identify the yeast strains whose behavior is less affected by the presence of copper.  

For this reason, a first test was conducted on different natural white musts, contaminated or not with 10 mg/l of Cu2+, trying to mimic as much as possible what happens in the cellar. 15 active dry yeasts have been compared, outlining a common effect of acetaldehyde increase due to copper presence, but displaying a high strain and must-dependent individual behavior in terms of amounts of SO2 and acetaldehyde produced. 

To investigate the impact of Cu2+ on yeast metabolism under more controlled conditions, a subset of relevant strains was compared in a synthetic must [5], added or not with Cu2+. The influence of fermentation temperature was also evaluated, carrying out the experiments at 16, 18 and 20°C. Fermentation kinetics, free and total SO2 production, and acetaldehyde production were monitored. The results confirm the common observation of increased acetaldehyde production in the presence of copper, while also confirming strain-specific responses which resulted more stable than in natural must. Regarding temperature effects, beyond the expected impact on fermentation duration, our initial findings suggest that temperature influences the magnitude of the difference between copper and control conditions.