Tannin structure-activity correlations during red wine extraction operations

Tannins, which are polyphenolic polymers derived from grape skins and seeds, are considered to be the main responsible factor for red wine astringency. With that having been determined, managing these compounds�quantitatively as well as qualitatively�had been a priority for the wine production industry. Skin and seed soak time is a process adapted by winemakers in order to extract phenolics into the wine matrix, ultimately reaching desirable mouthfeel qualities. This study was developed in order to investigate the relationship between extracted tannins and their associated composition and their effect on astringency (by means of measuring hydrophobic interaction). Multiple analytical methods were chosen in order to determine molecular size, subunit composition, red color incorporation, and extent of oxidation. The goal was to correlate the aforementioned structural variables to tannin activity in order to determine the driving force behind tannin affinity towards hydrophobic surfaces during fermentation/maceration. The study found that tannin activity is mainly driven by molecular size. Compositionally, subunits that are seed-like increased tannin activity, while skin-like tannins decreased activity. Red color incorporation into the tannin polymer decreased tannin interactions with hydrophobic surfaces. Conversion yield suggests that tannin oxidation reduces tannin activity.