Wine aging color changes during

Some structural changes of the native flavonoids occur during wine conservation, and one of the most studied of those changes concerns red wine color evolution, called wine aging. It has been demonstrated that as a wine ages, the initially present grape pigments slowly turn into new, more stable red pig-... 

Finally, we try to develop a chemical interpretation for the color of red wine—i.e., the specific role of different substances and the changes they undergo which cause the evolution of wine color, especially during aging. 

Interpretation of Wine Color and its Changes during Aging... 

The phenolic compounds extracted from the fruit contribute to the development and stability of the wine s red color. The color evolution during vinification and aging is mainly due to chemical transformations to the phenolic compound derived from the fruit. Anthocyanins, responsible for the purple-red color of young wines, participate in reactions with other phenolic compounds to generate other, more chemically stable molecules. These changes involve oxidation, polymerization, and other... 

Bakker, J., Picinelli, A., and Bridle, P. (1993). Model wine solutions Color and composition changes during aging. Vitis 32,111-118. 

The probable involvement of xanthylium salts in red wine color change is supported by the fact that their absorption maxima match well with the increase in yellow color around 420 nm observed during ageing of red wine. Thus, Liao et al. (22) demonstrated in model systems that reactions between anthocyanins and flavan-3-ols give rise to orange-yellow (440 nm) pigmented products. Based on the earlier observations of Jurd Somers (24) and Hrazdina Borzell (48 such products have been postulated to be xanthylium salts proceeding from direct anthocyanin-flavanol adducts. 

Ethanal is the most important of these compounds (Table 2.6). The many ways it can be produced and its high reactivity (the CHO radical has extensive chemical affinities), as well as its rapid combination with sulfur dioxide at low temperatures and its organoleptic properties, make ethanal a very important component of wine. The presence of ethanal, produced by the oxidation of ethanol, is closely linked to oxidation-reduction phenomena. It is involved in the alcoholic fermentation mechanism. Furthermore, ethanal plays a role in the color changes occurring in red wines during aging by facilitating the copolymerization of phenols (anthocyanins and catechins) (Section 6.3.10). 

Once again, the detection of these pigments in wines reinforces the importance of acetaldehyde as an intermediary in the chemical transformations that occur in red wine during aging, leading to the color change. 

During aging, the tannins become softer as they polymerize or combine with anthocyanins, while coloring matter precipitates and the color changes. The less oxidized ruby ports maintain the fruitiness and robustness of young wines. They have a more or less dark red color. The older, more oxidized tawny ports are golden red or golden. 

Ortega, A. F., Lopez-Toledano, A., Mayen, M., Merida, J., and Medina, M. (2003). Changes in color and phenolic compounds during oxidative aging of sherry white wines. /. Food Sci. 68, 2461-2468. 

Changes in the color of red wines that occur during aging are due to the anthocyanins undergoing chemical reactions and polymerization with the other wine compounds. More than 100 structures belong to the pigment families of anthocyanins, pyranoanthocyanins, direct flava-nol-anthocyanin condensation products, and acetaldehyde-mediated... 

In wine, this type of reaction occurs at the same time as the heterogeneous polymerization of the procyanidins (Section 6.3.7), as a result of the controlled oxidation during barrel aging, when traces of ethanal are produced by the oxidation of ethanol. The color of the wine becomes more intense and changes tone, becoming darker after a few months in the barrel. 

Temperatures above 20°C are dangerous during barrel aging. Excessive heat may cause irreversible color breakdown and the formation of tannin polymers that do not always soften the wine. These changes are even more extreme in wines with a low phenol content and in oxidized media. It is always dangerous to barrel-age wines in cellars without temperature control. Furthermore, higher microbial risks are likely to lead to an increase in volatile acidity. 

During bottle aging, wines develop in a reducing environment, tending towards greater organoleptic quality than they initially possessed. Besides changes in color, this process results in an increase in the complexity and finesse of aroma and flavor. The time necessary to attain this optimum... 

Chaves, M, Zea, L., Moyano, L., Medina, M (2007). Changes in color and odorant compounds during oxidative aging of Pedro Ximenez sweet wines. Journal of Agricultural and Food Chemistry, Vol. 55, No. 9, (May, 2007), pp. (3592-3598), ISNN 0021-8561. 

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