Chapter 15 - Improvement and stabilization of red wine color

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From the basics of wine anthocyanins to the enological techniques aimed at improving and stabilizing red wine color, this chapter aspires to connect the theoretical background of anthocyanin chemistry with the practical side of red winemaking. At the outset, the structures of individual wine anthocyanins are illustrated and discussed in the context of the latest findings, assigning specific types of anthocyanins to certain grape varieties. A new graphical evaluation scheme demonstrates that the concentration of the red flavylium cation strongly depends on the interrelated influence of wine pH and free SO2 content; the latter results in a flavene 4-sulfonate, an anthocyanin derivative responsible for color loss in grape juice or young red wines after sulfurization. Among anthocyanin-derived pigments, new data obtained from red wine shows that acetaldehyde, representing the most abundant aldehyde in wine, triggers the formation of flavan-3-ol-anthocyanin adducts with up to three ethylidene bridges, possessing higher color stability than free anthocyanins. Changes in anthocyanin concentrations and fingerprints during winemaking and maturation are highlighted, as well as the enological techniques influencing the concentration of anthocyanins. As prominent examples, prefermentative maceration, juice runoff, fermentation temperature, thermovinification, tannin addition, barrel aging, and micro-oxygenation are discussed with respect to red wine color, allowing valuable information about color stabilization for wine professionals and experts from other disciplines.