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WINEMAKING Highlights • Tannins from grape seeds have few fans among winemakers, but much of that bad reputation is based on misunderstanding. • Among the contributions of seed tannin are shorter, less as- tringent polymer chains—a likely boost to wine longevity and a component in building the mid-palate of wines. • Any comparison of grape seed and skin tannins is overshadowed by the changes both go through once they get into wine. Seed tannin-free red wine would be a mere shadow of the real thing. sensory studies, seed tannins should be, chain for chain, less astrin- gent than their skin-wrapped cousins. Seed tannin often comes with a chunk of gallic acid stuck to the end of the chain, and for some rea- son, that can make a seed tannin chain of a particular length rougher than a same-sized skin chain—even though gallic acid itself is not astringent. But the chances are good that once that seed tannin gets into the chemical kickboxing of a wine solution, gallic acid will get knocked off, lessening the seed tannin astringency. In other words, if you have a highly tannic wine, chances are the seeds weren't responsible for it. The shortness of seed tannin also has a downside: bitterness. For some reason bitterness, at least in tannin, is only perceived in the presence of large amounts of low-molecular-weight com- pounds, so the shorter seed chains are more likely to come across as bitter than the longer, higher-weight skin chains. Jim Kennedy at California State University, Fresno, thinks that our bitterness taste receptors may not be big enough to deal with the long chains, so they get a pass and only produce astringency. Harbertson thinks the big ones may get caught up in saliva proteins before they ever get to the taste buds. In any case, seed tannin is one potential source of bitterness—depending, of course, on what happens to those little chains once they get into wine. Finally, seed tannin is much more plentiful than skin tannin. Har- bertson estimates a range of 3.5 to 5 milligrams (mg) of seed tannin and 0.5 to 0.9mg of skin tannin per berry. Kennedy observes that viticultural practices can have a substantial effect on accumulations of both types of tannins: low-vigor vines tend to produce grapes with more skin tannin and more astringency; high-vigor vines pro- duce grapes with more seed tannin and more bitterness. Then the grapes get picked and the real fun starts. Grape tannin and wine tannin Phenolics researchers all agree that we know more about tannins in grapes than tannins in wine—which are, after all, the ones we actually taste. Once the grapes hit the crusher, tannins and most everything else segue into an alternate reality. Even though seed tannins are more plentiful, water-soluble skin tannins come out earlier and easier than seed tannins, which stub- bornly insist on ethanol as a solvent. Except possibly in cases of extreme extended maceration, during which seed tannins continue to be extracted, skin tannins constitute the great majority of in- puts. In this light, Jim Kennedy says that the issue for winemakers isn't so much controlling seed tannin as managing skin tannin. But far more than the seed-to-skin ratio changes. Australian Wine Research Institute (AWRI) phenolics researcher Paul Smith advises, "Forget everything you know about structure-function relation- ships for grape tannins. Forget about short or long, seed or skin, galloylated or non-galloylated. Of course all tannin comes from grapes, but once it's extracted most of it rearranges, breaks apart, recombines, binds more polyphenols, anthocyanins, acetaldehyde, etc., and what is left is 'wine' tannin, of which a small amount of material, chemically, still looks like grape tannin. We regularly see that wine tannin can be less than 20% 'grape' tannin." Sounds almost Biblical, doesn't it? "The long shall be short, and the short long, and the skins will lie down with the seeds." At this point in tannin studies, the 80% of wine tannins that aren't simple grape extracts are not well understood. "Characterizing the Tannins: The essential element. TANIN VR SUPRA® (IDP) Synergistic combination of ellagic and proanthocyanidic tannins, naturally purified in phenol acids, for the vinification of red wines. • Structure improvement. • Strong reactivity with proteins (grape tannins protection). • Laccase activity inhibition. • Antioxidant (color protection). • Clarification improvement. 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