Effect of the Substitution of Sulfur Dioxide by Tannin Fractions from Wine Pomace before Alcoholic Fermentation on the Flavor Quality of Wine

This study was undertaken in order to investigate the effect of adding four tannin fractions from wine pomace to replace sulfur dioxide (SO₂) before fermentation on wine flavor quality. Cabernet Sauvignon wine pomace was selected as raw material for the extraction and purification of grape skin high-polymer tannin (HRSK), grape skin low-polymer tannin (LRSK), grape seed high-polymer tannin (HRSD), and grape seed low-polymer tannin (LRSD). Before alcoholic fermentation for red wine-making, the four tannin fractions and SO₂ were separately added. Samples with nothing added served as control. The six wines were analyzed for basic physicochemical indexes, CIELab color parameters, redox potential, total tannin and total phenol contents, volatile components and sensory quality. The results showed that there was no significant difference between the four tannin and the SO₂ groups in terms of color indexes, total tannin, total phenol contents, bitterness or astringency, which indicated that substitution of tannins for SO₂ did not affect the changes in wine color, taste or flavor. In addition, it was found that compared with SO₂, the four tannins significantly reduced the content of 3-methylthiopropanol in wine while significantly reducing the perceptible reduced off-flavor. Aroma analysis by gas chromatography-mass chromatography (GC-MS) revealed that the addition of HRSD resulted in higher contents of volatile constituents such as alcohols and esters compared with the other treatments, the effect being similar to that of SO_2. In conclusion, wine pomace tannins can be used as an alternative to SO₂ in wine-making, and the effect of HRSD is the most pronounced.