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The copigmentation effect of prefermentation additions of different doses of caffeic acid was investigated during the 1997 harvest. Microfermentation with the major red grape cultivars Listán negro and Negramoll, grown in the Canary Islands, was carried out with the same protocol. Visible and UV spectra were registered periodically. HPLC chromatograms were carried out. The color enhancement of cv. Negramoll wine varied between 13 and 75% (AU at 520 nm), and that of cv. Listán negro wine between 25 and 45% at the end of fermentation. During aging these values were enhanced to reach even >100% in some cases. An initial complex of the 1:1 type, where one molecule of caffeic acid associates with one molecule of anthocyanin, has been identified using the mathematical procedure of Brouillard et al. (J. Am. Chem. Soc. 1989, 111, 2604-2610). Caffeic acid seems to contribute to color stability and protection against oxidation. The importance of nonpigment composition in pigment extraction and color retention during and after fermentation is demonstrated.

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Copigmentation and enological parameters were studied in a collection of 250 red wines. Although several copigmentation studies have been performed with model solutions, little is known about the actual consequences directly in wine of anthocyanin interactions. To date, some studies have considered relationships between copigmentation and natural wine constituents, but none correlates copigmentation measurements with the real wide concentration in wine. In this work, published hypotheses based on model solutions such as phenolic acid copigmentation ability or the influence of copigmentation factors such as flavonols are empirically evaluated in a large sample of wines for the first time. The study confirms previous results obtained from solutions, whereas other factors suggested as being relevant seem to be unrelated to the studied effect at the concentration range naturally occurring in the wines studied. For instance, the important role of flavonols and hydroxycinnamic acids has been ratified, whereas ethanol, gallic acid, and some metals show significant inverse correlations with copigmentation. Unexpectedly, magnesium content in wine correlates with color, whereas the concentration of traditional copigments, such as quercetin, does not show any correlation with copigmentation.

Chromatic characteristics and their relationships with copigmentation and phenolic composition were studied in 160 bottled red wines. Free anthocyanins, copigmented anthocyanins and polymeric pigments contributing to color were calculated according to Boulton protocol and related to main changes produced in wine visible spectra after destroying any copigmented anthocyanins effect. Color differences between copigmented and non copigmented wines were quantified and related with ageing, cultivar and phenolic profile. Phenomenon of co-pigmentation visually increases the colour at 420, 520 and 620 nm for most of wines. Copigmented wines showed a mean value of 8.26 CIELab units higher than non copigmented (ΔE ab(cnc) ), being this shift deeper for young wines than for aged wines. Copigmentation mostly changed hue and decreased L, a* and b* values therefore resulted into purplish and darker wine. Visual variations in color caused by copigmentation was related to particularly anthocyanins and copigments (mostly flavonols and hydroxycinnamic acids).

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