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The composition of skin cell wall material from Pinot noir and Cabernet Sauvignon grape berries from four different regions in California were investigated to determine relationships between cell wall composition and phenolic extractability observed under winemaking conditions. Multiple vineyards (sites) per region were studied. Cell wall composition analysis included the determination of total soluble sugars, proteins, non-cellulosic glucose, cellulose, lignin, lipids, total polyphenolic content, soluble polysaccharides, and uronic acid, as well as the isolation efficiency. Results indicated that cell wall material (CWM) composition is mainly site-specific with some impact due to variety and little to no impact due to the growing region. Grape phenolics analyzed included monomeric flavan-3-ols, anthocyanins, polymeric phenols and polymeric pigments and could be used to distinguish between varieties. Grapes grown in the same region exhibited similar phenolic extractability indicating a significant impact of the growing area as well as a synergistic effect between CWM composition and grape phenolics. CWM composition analysis indicated that demethylation of pectin favored the release of phenolics, while lignin content correlated negatively with the phenolics extracted. Proteins showed a negative correlation with polymeric phenols whereas no correlation was found with polymeric pigments. Anthocyanin extractability was highly impacted by its content within grape skins, more so than other phenolics that are present in both the skins and seeds.

The effects of temperature and concentrations of ethanol and anthocyanin on the adsorption and desorption processes of anthocyanin onto cell wall material were investigated. Independent variables included temperatures of 15 and 30°C, model wines with ethanol concentrations of 0 and 15%, and anthocyanin concentrations of 1, 1.5, and 2 g/L. These experiments were conducted in triplicate in bench-top solutions that mimicked a single-berry fermentation environment. Desorption experiments were carried out immediately after completing the adsorption experiments to minimize changes on the cell walls that may have affected the kinetics of the process. Results indicate that more than 90% of anthocyanin adsorption occurred within the first 60 min of interaction with cell wall material. However, desorption appeared to occur much faster; a maximum was reached after 30 min. Temperature and concentrations of ethanol and anthocyanin were found to have a significant effect on both adsorption and desorption kinetics. Results show that phenolic concentration in the final wine not only depends on the amount released from the grapes but also on its interactions with the solids in the fermentor. Additionally, these interactions are dependent on temperature and ethanol concentration.