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32 p r a c t i c a l w i n e r y & v i n e ya r d J a n U a r y 2 0 1 5 W I N E M A K I N G Matthew R. Revelette, Ralph S. Yacco and James A. Kennedy, Department of Viticulture & Enology, California State University, Fresno, Calif. BY T here is an incredible range of sensory descriptors that refer to red wine tannin. Words such as silky, velvety, dusty, green or hard have all been used by winemak- ers, wine writers and consumers from around the world when referring to tan- nins in wines. What is the underlying chemistry that leads to these descriptors? Developing a standardized vocabulary of mouthfeel descriptors 1 and the chem- istry responsible for these descriptors 2 is essential if we are to effectively manage red wine mouthfeel in the vineyard and winery. Our goal as tannin researchers is to understand the chemistry of astringency so that viticulturists and winemakers can manage mouthfeel and astringency more effectively. Red wine tannins are derived primar- ily from the skins and seeds of grapes and are extracted during fermentation and maceration. 3 The concentration of this extracted tannin plays a significant role with regard to astringency, but it does not tell the entire story— anecdotes abound regarding wines that have simi- lar tannin concentration but have tex- tural mouthfeel characteristics that are inexplicably different. For example, the transformation of red wine mouthfeel during micro-oxygen- ation is an indication that wine matrix components (Figure 1), while important in tannin perception, do not fully explain mouthfeel descriptors. In order to bet- ter understand tannins within wine, we need to develop a methodology to deter- mine not only the tannin concentration but also how active that tannin is. Astringency and mouthfeel management Astringency in red wine is considered to be a result of the precipitation of salivary proteins by tannins and/or the binding of tannins to our oral mucosa. 2 Tannin structure and subsequently the astrin- gency of wine is modified throughout the various winemaking processes and proceeds through development in the bottle of the finished product. Astringency perception in wine may be modified in several ways that we can broadly refer to as mouthfeel manage- ment (Figure 2). The "wine matrix" plays stickiness New concept in grape and wine tannin analysis gent than seed tannins and greater pro- portions of skin tannins have also been found to correlate with higher percep- tions of quality and price point. 7,8 The size of tannin polymers also has an effect with larger (higher molecular mass) tan- nins correlating with an increase in per- ceived astringency. 9 Tannin compositional effects such as skin/ seed tannin proportion, polymer size distribution, color incorporation and degree of oxidation are all considered to be of critical importance to understanding the sub-qualities of astringency in wines. Recently, a great deal of attention has been given to the incorporation of antho- cyanins (the phenolic responsible for color in red wine) into the tannin poly- mer. Referred to as pigmented polymer, these tannin-anthocyanin products are thought to be less astringent. 8 Tannin oxidation during élevage and develop- a role with acidity, alcohol concentration, residual sugar, mannoprotein and poly- saccharides all contributing in various ways to the mouthfeel of a wine. Acidity, for example, in wine increases both bitterness and astringency, while an increase in alcohol concentration reduces perceived astringency while increasing bitterness and contributing to the "body" of a wine. 2,4,5 Residual sugar contributes to the sweetness of wine, which attenu- ates astringency. Yeast-derived mannoproteins and grape-derived polysaccharides interact with tannins in wine and can inhibit their astringent qualities. In a perfect world, knowing the tannin composition and concentration would tell us all we need to know about the perceived astrin- gency it would produce, but wines are never that simple. Research has shown that astringency correlates with tannin concentration, In general, the higher the tannin concen- tration, the more astringent the wine becomes. 6 However, tannin composi- tional effects such as skin/seed tannin proportion, polymer size distribution, color incorporation and degree of oxida- tion are all considered to be of critical importance to understanding the sub- qualities of astringency in wines. 2 Skin tannins are less bitter and astrin- Figure 1. Generalized view of the role that tannin concentration and composition, in conjunction with wine matrix elements, play in mouthfeel description. Perceived Tannin Colloidal State Direct Oxida on Antho- cyanin Organic Acid Residual Sugar Aroma Compound Poly- saccharide Ethanol Glycerol Oxida on Products Manno- protein Tannin Concentra on Composi on Our percep on of tannin is influenced by many wine components Figure courtesy oF James a. Kennedy