Influence of Potential Alcohol in Grapes on Phenolic and Sensory Characteristics of Red Wine.

Potential alcohol, as obtained by grape maturity, affects the extraction of phenolics during winemaking. The extent to which potential alcohol is correlated to phenolic and sensory characteristics of red wine was investigated. Decoupling of the ripening kinetics of grape constituents due to climate change emphasizes this question. The impact of potential alcohol, as naturally obtained by grape maturity or adjusted by sugar addition, representing high sugar but low phenolic maturity, on wine characteristics was investigated for two varieties over two vintages. Enhancement of potential alcohol to late harvest conditions did not achieve the sensory characteristics of wine made from phenolic mature grapes. An experimental model was developed revealing the contribution of potential alcohol to phenolic and sensory characteristics. In Pinot noir, anthocyanins correlated well with natural potential alcohol but were not influenced by enhanced potential alcohol. In Cabernet Sauvignon, polymeric pigments provided the most accurate information about grape maturity perception in wine.

Grape-derived pectic polysaccharides alter the tannin and pigment composition of Cabernet Sauvignon red wines.

Tannins, anthocyanins, and polymeric pigments are essential phenolic constituents of red wine because they provide color, color stability, and mouthfeel properties like astringency. The behavior of these compounds is significantly affected by pectic polysaccharides, whereby the extent of their influence on red wine quality depends on their structural features and their interactions with the polyphenols. In the present study, the composition of the pectic polysaccharides of commercially available Cabernet Sauvignon wines and their impact on anthocyanin, tannin, and polymeric pigment analyses was characterized. This was accomplished by preparation of polysaccharide deprived wines and comparison of the polyphenolic composition of both, the wines and their corresponding polysaccharide-free counterparts. The results show that the cell wall fragments enhance the spectral absorbance of anthocyanins by facilitating anthocyanin self-association, leading to a co-pigmentation-like effect. Low molecular weight pectins like rhamnogalacturonan II and polygalacturonic acids with a low degree of esterification are assumed to form soluble complexes with anthocyanins and also prevent protein precipitation of tannins, which was reduced by 6-13%. High molecular weight pectins with a high degree of esterification lead to the increased precipitability of pigments and tannins by a factor of 1.3 to 32.4 and 1.1 to 1.9, respectively, seemingly impairing the incorporation of anthocyanins in tannins to form precipitable polymeric pigments that are responsible for the longevity of red wine color. The increased precipitability of the pigments due to the interactions with the polysaccharides may indicate the formation of pigmented yet non-covalent aggregates that show comparable properties to the covalently formed precipitable pigments. The formation of those non-covalent structures may affect red wine color stability and astringency.

Influence of Grape Cell Wall Polysaccharides on the Extraction of Polyphenols during Fermentation in Microvinifications.

Grape cell wall polysaccharides influence the extraction of phenolic compounds during winemaking and consequently polyphenol concentrations in the final wine. During ripening, both compound groups undergo pronounced structural and compositional changes, resulting in a dynamic change of extractability. Grape cell wall polysaccharides from different ripe grapes were added to fermentations of Cabernet Sauvignon and Pinot noir grapes. Polyphenol-polysaccharide interactions affected the concentrations of tannins and monomeric flavanols in the wines depending on the maturity of the added polysaccharides. With higher polysaccharide maturity, the effects became more pronounced. Polysaccharides protected monomeric flavanols and tannin in Pinot noir, thereby increasing the concentrations, but they precipitated or masked these compounds in Cabernet Sauvignon. The added polysaccharides affected the concentrations in anthocyanins and polymeric pigments much less compared to the ripening status of the grapes. It was concluded that structural changes of polysaccharides during ripening affect the extraction of tannins and monomeric flavanols the most.