Polyphenols are important compounds in red wine, and mechanisms for their extraction have been studied intensively. Especially in red wine, grape skin polyphenols are vital contributors to taste and color. However, skin tannin rapidly decreases in red grapes such as Muscat Bailey A (Muscat Hamburg × Bailey, MBA) during must fermentation. In this study, we focused on the adsorption of tannin to insoluble polysaccharides from grape skin and carried out experiments on model wine solutions (12% ethanol and 5 g/L potassium bitartrate) at pH 2.5 to pH 5.0. At pH 3.5, ~30% of skin tannin adsorbed to insoluble polysaccharides from grape skin. High (70%) and low (30%) affinities with skin tannin were noted at certain pH values (pH 4.2 and pH 3.2). We also examined must pH that affects MBA skin tannin extraction in model experiments. MBA skin tannin was extracted into model wine at pH 3.2, 3.7, or 4.2. Bovine serum albumin (BSA) binding tannin concentrations were analyzed (protein precipitation method). At pH 3.2, double the skin tannin was extracted than at pH 4.2. The results suggest that must pH in fermentation is important for skin tannin extraction into red wine.

Funding Support: Grant-in Aid for Scientific Research