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uble wine tannins are more astringent, while smaller wine tannins that are less water-soluble, have more color and more oxidative structures were perceived as hotter, more bitter and less astringent. These results demonstrate that different types of tannins can influence mouthfeel and confirmed that modifying wine tan- nin structures during winemaking is a practical path to altering wine mouthfeel. ÉLEVAGE Color development and stability During red wine élevage and post-bot- tling maturation, winemakers hope for the formation of long-term stable, red color. Yet in some situations, color is inadequate from the beginning or is unstable and fades fast. While some of the factors influencing stable color forma- tion are known, others remain a mystery. One of the main reasons for the color change seen in wine during élevage and post-bottling maturation is the decrease in anthocyanins (red pigments derived from grapes) and changes to pigmented tannins (stable colored compounds formed by reactions between anthocya- nins and tannins). Analysis of 30- and 50-year vertical series of Cabernet Sauvignon and Shiraz wines showed that wine color density was more strongly associated with pig- mented tannins over the 30- and 50-year series than with anthocyanins (after the first two years post-bottling), clearly reinforcing the importance of pigmented tannins to wine color. In general, after four years no colored anthocyanins were left in red wine. 16 In a separate experiment, wine color density was tracked through three years of maturation in wines of both high phe- nolic potential (high anthocyanin, high tannin) and low phenolic potential (low anthocyanin, low tannin). 6 Higher wine tannin and anthocyanin led to enhanced wine color density and stable non-bleach- able pigments, which were retained through maturation. Formation of non- bleachable pigments was found not to increase beyond two years of maturation. The incorporation of color during fermentation through to post-bottling maturation was proportional to tan- nin concentration. Non-bleachable pig- ments were formed via multiple routes, such that high-tannin, high-anthocy- anin wines formed greater quantities of both polymeric and non-polymeric red pigments. Further work is required to understand how these alternative mech- anisms for stable pigment formation can be harnessed. To summarize, low tannin concentra- tion does not necessarily prevent the formation of stable non-bleachable pig- ments, but high tannin concentration maximizes the likelihood of long-term color stability. Astringency changes Analysis of the vertical series also clearly indicates that aged red wines can have similar tannin concentrations to young wines, dispelling the commonly held belief that changes in red wine astrin- gency with post-bottling maturation are due to the loss of wine tannins through precipitation. Such changes in astrin- gency are instead due to compositional changes in tannins, although the rate of these changes is unknown. The structure of tannins isolated from older wines were analysed to try to understand the changes observed in astringency as wines age. 15 The "aged wine tannins" were shown to only weakly associate with saliva-like pro- teins compared to tannins from younger wines. This is consistent with observed lower astringency of old wines, as the sensation of astringency is linked with strong association between tannins and salivary proteins. In addition, the analysis revealed a large proportion of tannin that can- not be broken apart (tannin that is size of tannins, increased stable color formation and reduced the astringency of the wines compared with wines not treated with air. 10 This new knowledge provides practical options for winemak- ers to influence tannins during fermenta- tion. Impact of novel yeasts on tannins to improve wine quality Yeasts are well known to influence wine aroma, but their effect on macromol- ecules and texture has been less well explored. A selection of yeasts were investigated for their effects on color and tannin and were shown to influence final tannin concentration by up to 50%, and to also significantly affect wine color. 20 Further studies that evaluated the impacts of fermenting Shiraz and Pinot Noir with different yeast strains again showed a strong influence of yeast strain on tannin concentration. 9,11 For example, in experiments with Shiraz and Cabernet Sauvignon, wines made with S. bayanus strain 1375 and S. bayanus AWRI 1176 (Australian Wine Research Institute) had consistently low tannin concentrations whereas wines made with S. cerevisiae AWRI 1486 had generally high tannin concentrations. With all strains, the tannins in the wines were highly pig- mented. This work demonstrates that the color and texture of red wines can be significantly modulated by choice of commercially available wine yeast. Tannin measurement now widely available In the past, lack of accessibility of meth- ods to measure tannin has been a bar- rier for winemakers in optimizing wine tannin and color. Development of the simplified methlycellulose precipitation (MCP) tannin assay was the first step in breaking down that barrier. This method is published in the widely used Chemical Analysis of Grapes and Wine; Techniques and Concepts handbook by P. Iland et al., 12 along with data from the Australian wine tannin survey, which communicates what can be considered low, medium and high tannin concentrations. An even simpler option is the web-based tool offered by the AWRI that allows producers to mea- sure and benchmark tannin and color in both grapes and wine. This tool forms a component of the WineCloud. Investigation of compounds with sensory impact The importance of the structure of red wine tannin in influencing wine mouth- feel has been investigated. 18 The study showed that larger and more water-sol- • Acidity • Ethanol • Residual sugar • Mannoproteins • Polysaccharides • Amount • Skin/Seed • Size distribution • Color Incorporation • Tannin oxidation Figure courtesy oF James a. Kennedy Figure 2. The management of wine mouthfeel can be separated into three broad categories including matrix elements, tannin concentration, and tannin composition. 18 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