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Wine flavor and quality are determined by the assessment of multiple sensory stimuli, including aroma, taste, and mouthfeel. It is therefore important to consider the contribution of as many metabolites as possible when attempting to relate wine composition to quality. In this study, partial least squares regression of the volatile (untargeted headspace solid-phase microextraction coupled with gas chromatography time-of-flight mass spectrometry), non-volatile (untargeted reverse-phase ultrahigh-performance liquid chromatography mass spectrometry), and combined metabolite profiles were used to predict Pinot Noir wine quality ratings as assessed by experts. Non-volatile metabolite profiles predicted wine quality ratings better than volatile metabolite profiles, suggesting that the non-volatile composition of Pinot Noir wines contributes to quality perception to a greater extent than the volatile composition. This was underscored by descriptive sensory analysis, which found that taste and mouthfeel attributes were better correlated with wine quality ratings than aroma attributes. Important predictors of Pinot Noir wine quality were also characterized. Some new relationships between wine metabolites and quality ratings were found: dipeptides and unsaturated fatty acids were positively related to Pinot Noir wine quality, while N-(3-methylbutyl)acetamide and xanthine were negatively associated.

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Grape marc, also known as grape pomace, is an underutilized biowaste composed predominantly of grape skin and seeds that is produced as a byproduct of winemaking on the milliontonne scale annually. The most important high-value current use of grape marc is in the production of oenological tannins, widely used additives in the food and beverage industry. More commonly, grape marc is simply either disposed of or used as feed or fertilizer. With recent evidence showing that extracts enriched in grape tannins contain significant amounts of the thiol precursors Cys-3SH and GSH-3SH and the possibility that these could influence food and beverage aroma, it was decided to investigate grape pomace extraction procedures in order to try to define extraction protocols that could maximize the recovery of these compounds from grape marc. Should such an extraction protocol be shown to be commercially viable, this could lead to further utilization of material that would otherwise be disposed of. Two thiol precursors and eight monomeric phenolics (quercetin 3-O-glucoside, quercetin, resveratrol, grape reaction product, trans-caftaric acid, catechin, epicatechin, and gallic acid) were identified and simultaneously extracted from Sauvignon Blanc grape marc using solid−liquid extractions. The optimal solvent ratio of acetone:water:EtOH was explored for each compound. Ten ternary diagrams were constructed, showing the effectiveness of extraction across 66 different solvent combinations using the aforementioned solvents. Effective extraction of thiol precursors was dependent on a high water content which is an advantage from an economic and environmental perspective, while for the most abundant phenolic, quercetin 3-O-glucoside, optimal extraction levels (1017 mg per kg of grape marc) were achieved using a 40:50:10 solvent mixture. In addition, this manuscript details the first extraction of thiol precursors from grape pomace which adds a significant potential commercial value to this underutilized byproduct.

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