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non-hydrolysable), unlike grape tan- nin, which is readily broken apart. This non-hydrolysable proportion of wine tannin has also been shown to have a very weak association with saliva- like proteins and accounts for a larger proportion of aged wine tannins than young wine tannins. These results may, at least in part, explain why red wines "soften" with age. An additional experiment demon- strated that tannin structure in Shiraz wines is not influenced by storage at dif- ferent pH levels (3.2, 3.5 and 3.8) or under different screwcap closures with specific oxygen-transfer rates after two years of bottle storage, even though wines of lower pH are often reported as more astrin- gent. 17 This suggests that a lower pH has a direct effect on sensory perception of the wine examined, but does not necessarily influence wine tannin evolution. These results provide improved insight into the stability of tannins in wine and under- score the importance of wine matrix influ- ences on perceived mouthfeel. Overall, astringency has been dem- onstrated to depend on the type of tan- nin and not just the amount present. In the future by targeting the creation and retention of specific types of tannins, it should be possible to create wines that have the softer mouthfeel of an aged wine, but at a much younger age. CONSUMER Higher tannin does not always mean more consumer preference A trial was conducted where Cabernet Sauvignon wines were produced from grapes from the same vineyard har- vested at five different maturity stages. The wines were found to have significant differences in tannin and color, with lower alcohol (12%) wines having lower tannin, a lower proportion of skin to seed tannin and less color and polymeric pig- ment compared to higher-alcohol wines (15%). 7 Astringency increases were correlated with higher tannin for later harvested wines. 8 In the experiment, the five wines were presented to a group of consum- ers who rated how much they preferred the different wines. Results showed that wines of 13% alcohol or higher were pre- ferred compared to lower alcohol wines. However, no further increases in con- sumer preference were observed for the wines between 13% and 15% alcohol, despite increases in tannin. Importance of tannin structure on wine quality There continues to be demand from industry for understanding as to how wine tannin composition (not just con- centration) influences quality, wine grad- ing or price, and research has addressed the role of tannins in the quality/grad- ing/price nexus. 19 Quality (defined as winemaker-assessed grading that ultimately relates to market price) in young red wine was positively correlated with tannin concentration, tan- nin size, higher proportion of skin-derived tannins and overall wine color (see Figure 3). 13,14 This suggests that maximizing skin tannin concentrations and/or proportions in wines can contribute to an increase in projected wine bottle price, but this must be done in balance with other wine com- ponents which contribute to the desired wine style. Management factors associated with increased skin tannin concentrations include: • reduced vine vigor and vine water sta- tus, • increased fruit exposure, • increased berry crushing prior to fer- mentation, combined with reduced soak time, • use of enzymes. Conclusions Effectively managing vineyards and winemaking to optimize grape and wine tannin and color translates into increased capacity for the Australian wine industry to meet wine specification, consumer expectations and profitability. Specific areas where winemakers can now take practical steps to influence wine tannin include: • choice of yeast, • management of oxygen during fermen- tation, • viticultural and winemaking choices that aim to maximize proportions of skin tannin. Tannin research at the AWRI has pro- vided the Australian wine industry with an improved understanding of struc- tures, measurement, formation and func- tion of phenolics compounds responsible for wine texture and color, and it has significantly progressed the scientific framework for improvements in wine- making. Several areas have been identified with potential to return high value and knowl- edge gaps for future research. In particu- lar, the importance of understanding how tannins, proteins and polysaccha- rides work together in wine represents a research opportunity with significant potential to support production of desired wine styles. This work is con- tinuing in Project 3.1.4 of the AWRI's R, D&E plan 2013 –2018. PWV This text was edited from first publi- cation in the March/April 2014 Wine & Viticulture Journal with permission of the publisher, Winetitles. 20 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 Figure courtesy oF James a. Kennedy Tannin: • Concentration • Molecular Weight • % Epigallocatechin • Pigmented Polymer Wine Color Density Figure 3. Results from the analysis of a large set of wines and comparison with winemaker assessment of overall wine quality indicates that overall wine quality is related to phenolics over a large portion of the wine quality spectrum.