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T i m P atterson Inquiring Winemaker The Sticky Side of Tannin Management T op researchers from around the world gathered at an all-day Tannin Symposium held in conjunction with the annual meeting of the American Society for Enology and Viticulture in June. But the biggest tannin buzz came from another presentation given the day before, one that was generating reference after reference in subsequent panels. I'm not sure enologists make much use of Twitter to air what's on their minds, but if they did, this paper would surely have been trending, with the hashtag #hybridtannin. The unlikely object of attention was a talk by Lindsay Springer of Cornell University based on work she and her advisor, Gavin Sacks, had done on tannin extraction from French-American hybrid grape varieties. Hybrids might seem an odd focus for examining tannin extraction, since they are notorious for producing virtually tanninfree wines, but that was exactly the point. The refusal of hybrids to yield their tannins to any and all exertions by winemakers turned out to be a great way to shine a spotlight on the dicey, unpredictable movement of tannins from grapes to wine. Hybrids may be an extreme case, but even for mainstream vinifera, the relationship between tannin levels in the fruit and in the resulting wine is anything but straightforward. Sugar turns into alcohol in a predictable fashion, and acid comes across as acid, but tannin levels in grapes are not a reliable harbinger of tannin levels after fermentation. Some lots of high-tannin Cabernet come out wimpy; some lots of tannin-shy Pinot Noir come out hard as nails. Extraction is the first link in the chain of tannin management in the cellar, and it's full of mysteries. The most irritating part is there's not a lot winemakers can do about it. 24 W in es & V i ne s NOV E M B E R 20 13 Certainties and uncertainties Some pieces of this puzzle are pretty clear. Some varieties tend to have higher concentrations of tannins than others—Cab more than Pinot, for example. For any variety, the concentration in the berries is higher than in the wine they make; even badly over-extracted wines don't get everything the grape has to offer. Even though a number of winemaking techniques—macerating enzymes, more punch downs, thermovinification, extended maceration—can enhance extraction, some tannins always remain sequestered. (Much like parts of the Federal budget.) Or at least that's the pattern with vinifera grapes; hybrids seem more resistant to any winemaking blandishments. Researchers know that tannins are famously sticky, always looking for something to glom on to. Depending on the situation that might be protein, polysaccharides, each other, glass, whatever. It's this same tendency to be sticky that hitches Highlights •Unlike the straightforward conversion of sugar to alcohol, tannin extraction is unpredictable and erratic in both vinifera and hybrid grapes. • annin levels in finished wines are T always lower than levels in the fruit, with larger tannins particularly likely to get stuck in grape skins. • ybrid red varieties highlight the H problem; regardless of grape tannin, wine tannin is almost non-existent, in spite of processing methods. wine tannins to salivary proteins and produces astringency in the mouth. Not surprisingly, large-chain, higher molecular weight tannins seem to be the stickiest—or at least the stuckest. It's like Velcro; the more hooks and loops on a molecule, the more opportunities to fasten. Thus, proportionately fewer of the longer tannins make the extraction cut. Shorter seed tannins also are underrepresented, unless they come out during extended maceration. Thus the tannin length profile in wine is different from that in grapes, in addition to the differences in sheer amount. Some lots of high-tannin Cabernet come out wimpy; some lots of tannin-shy Pinot Noir come out hard as nails. Tannin binding mostly comes as weak bonds, either hydrogen attachments or hydrophobic hookups, aggregations of molecules seeking to avoid contact with water. These relatively weak bonds are, at least in principle, able to be broken up to some degree by one or another winemaking element—by heat, by ethanol, or various production techniques. Unless, of course, the grapes happen to be hybrids. Hybrids have the same kinds of tannins as vinifera grapes, and indeed the degree of vinifera parentage correlates well with the concentration of tannins. But they are reluctant to come out, or at least to stay out, under any circumstances, even though aggressive fermentation practices leave the skins utterly disintegrated, far more so than vinifera skins. This different behavior again suggests that we need to understand something about the cell walls, not just about the tannins. Skins and cell walls Skins, seeds and grape pulp all contain some tannin—and, of course, some cell walls. But skins are the main focal point of extraction studies; they only comprise 10% of the weight of grape berries, but they contain two-thirds of the cell wall