IX CONGRESO NACIONAL DEL COLOR - Publicaciones de la ...

IX CONGRESO NACIONAL DEL COLOR. ALICANTE 2010
RED WINE COLOR - RELATING COLOR TO COMPOSITION IN
YOUNG WINES AND PREDICTING THE COLOR OF AGED WINES
Roger Boulton
Department of Viticulture and Enology, University of California, Davis, CA, USA
Abstract:
Young red wines are considerably darker and different in color than would be expected from their
pigment composition. The extent of anthocyanin copigmentation, which can account for between
30 and 50% of young wine color, is directly related to the presence of other colorless components
found in the juice and especially the skins of grapes. The concentrations and identity of these
copigmentation cofactors varies widely between the grape cultivars and the conditions under
which they have been grown. The changes in this aspect of color due to the slow formation of
polymeric pigment are reviewed. A simple model for the formation of polymeric pigment and
these changes in color is presented. The role of the colorless cofactors and tannin, and
winemaking practices which influence these, on the color displayed by young and aged red wines
is described.
Keywords: Absorbance Anthocyanins, Copigmentation, Polymeric Pigments,
INTRODUCTION
The color of young red wines is primarily due to the anthocyanin pigments in the skin of
the grape, and the pH of the wine. The intensity of the color is almost doubled due to the solution
phenomenon of copigmentation, and there is generally a bathochromic shift of the order of 10 to
15 nm resulting in a more purple color, Boulton (2001). One unusual feature of this effect is that
colorless components, typically monomeric flavonoid and cinnamate cofactors, are essential for
these color enhancements. As red wines age they slowly build polymeric structures made up
primarily of colorless tannins and anthocyanins, resulting in a more red brick color typical of
these polymeric pigments. Aspects of winemaking, from the biochemical development of the
anthocyanin, flavonoid cofactors and the skin tannin in the berries, to the contacting conditions
during fermentation, to the levels of free sulfur dioxide, the extent of aeration and the period of
aging, all determine the color displayed in the young wine as well as that potentially displayed in
the aged wine. While the main pigment, malvidin-3-glucoside, is essentially stable to oxidation,
as are the polymeric pigments, most of the copigmentation cofactors are not and significant red
and purple color can be lost, and yellow and brown pigments formed, due to wine oxidation. The
time scale for these changes is of the order of years, so that red wines become a unique example
in the transitions in color in nature.
DISCUSSION
Color of Young Red Wines
The anthocyanins, A, in young red wines are in a dynamic equilibrium with colorless
cofactors, B, to form a complex with enhanced color, C. The ratio of cofactor to anthocyanin and
the strength of the complexing constant, Keq, determines the color enhancement as shown in
Figure 1. At low ratios, the cofactor is limiting, while at high ratios, the anthocyanin is limiting.
Red wines generally have ratios between 0.2 and 2.0 and the extent of copigmentation is
generally limited by the levels of the cofactors in the grapes.
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