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154 Wines&Vines January 2015 winemaking wine eaST To date, dozens of polymeric pigment types have been identified. Common adducts (or compounds formed from the direct addition of two other compounds) include anthocyanin- acetaldehyde; portosin, which contributes a blue color; vitisins, which are orange; and pi- notin, which enhances red color. A variety of tannin-anthocyanin and anthocyanin-tannin compounds also may form. It is likely that tan- nin concentration early in fermentation im- pacts polymeric pigment (but not copigment) formation. As with copigmentation, much of the sci- ence of polymeric pigment formation is still unclear. Concentrations are known to correlate positively with ethanol, but beyond that scien- tists can only speculate that any processing methods that increase the availability of oxy- gen and tannins required for hypothesized formation reactions will increase polymeric pigment content. These include micro-oxida- tion at the middle or end of alcoholic fermenta- tion, tannin additions early in fermentation, enzyme additions and saignée. Hybrid culti- vars, which have naturally low condensed tan- nin concentrations, will necessarily be limited in their potential for pigment formation. Wine color chemistry can be investigated two ways: by delineating individual chemical reactions (like anthocyanin-acetaldehyde bind- ing) and tracking them throughout the wine- making process; or holistically, by examining all the pigments in a finished wine and working back- ward to determine processing im- pacts on formation. In the latter case, a number of studies have yielded conflicting results about the impact of such methods as extended maceration and cold soak (which seem to have no im- pact), and freezing and thermov- inification (which may have some) on color enhancement. In short, given the variety of possible pigment complexes (many of which are still unknown), it's likely that the mechanisms and compounds that pro- vide "good" and lasting red wine color vary by cultivar, region and processing method. Tannins If color chemistry isn't confusing enough, tan- nin reactions and analysis are even more fun. Like "polymeric pigment," the term "tannin" is somewhat confusing. The broadest definition of tannins includes any plant polyphenolic capable of cross-linking collagen fibers in ani- mal hides, a categorization that is purely func- tional, and not altogether helpful from a winemaking standpoint. It does point to one important fact: Tannins are capable of precipi- tating proteins, providing the astringency and mouthfeel associated with high-quality red wines. From a winemaker's point of view, there are two types of tannin relevant to winemaking: condensed and hydrolysable. Condensed tan- nins are ogliomers or polymers (short or long chains) of flavan-3-ols, a family of small phe- nolic compounds including (+) catechin, (-) epicatechin, gallocatechin and gallocatechin gallate, the four most commonly found in tan- nin chains. These tannins originate in skins and seeds—and while seeds have a higher tannin concentration, they are less extractable, so skin tannin predominates in most wines. Concentra- tion of condensed tannins in the grape varies by cultivar, site and viticultural practices. Condensed tannins take many forms; vari- ables include the chain length (called degree of polymerization), the compounds that initiate WINEMAKING EFFECT ON COLOR, TANNINS Process Color enhancement Tannin extraction Cold soak None or (-) None Freezing (+) (+) Thermovinification None or (+) None Extended maceration None (+) Pectolytic enzymes Variable Variable