Influence of yield and harvest date on shiraz wine volatile and non-volatile composition

Targeted and untargeted metabolomics was applied to wine samples in order to determine the effect of yieldand harvest date on Shiraz wine volatile and non-volatile composition within the same warm-hot Australianmesoclimate. Vines were drip irrigated and trellised to open sprawling canopy with an average yieldfrom 10.2-18.5 kg/vine/vineyard. Shiraz wines were made in triplicates from grapes harvested at two occasions10 to 12 days apart (harvest 1; H1 and harvest 2; H2, respectively) commencing 12 days from theplateau of berry sugar accumulation.Most C6-alcohols, known to contribute to green/stalky and fresh fruit character in red wine, were significantly higher in Shiraz wines compared to the Cabernet Sauvignon wines. This was particularly noticeable for cis-3-hexenol, showing concentrations about 6-fold higher in the Shiraz wines. This finding was not observed for trans-3-hexenol. C6-alcohols are principally derived from the degradation of grape lipids during crushing and fermentation. However, the concentration of grape lipids and C6-compounds were poorly correlated with the concentrations of C6-alcohols in wine. Samples taken during fermentation showed that the differences in C6-alcohols between the two varieties were manifested at this stage, suggesting the importance of yeast metabolism to the final C6-alcohols levels. The influence of grape maturity on wine ester composition was also variety dependent, particularly for higher alcohol acetate and ethyl ester of branched acids. This study highlights that varietal differences observed in Shiraz and Cabernet Sauvignon wines involve fermentation-derived compounds, irrespective of the climate or irrespective of the site (soil x climate).