Wine aging tannin composition

D.3.5 Changes in Tannin Composition and Astringency During Wine Aging.556... 

A wine s behavior dnring aging therefore depends on a whole series of factors related to its composition. These inclnde not only phenol content, but also the type of tannins and their structures, as well as the tannin/anthocyanin ratio and the polysaccharide concentration. Fnrthermore, the wine s initial composition changes dnring aging, developing complex new strnctnres likely to slow down the process of stripping. 

There are obvious reasons for the slow progress in the characterization of colored matter in red wine. If one takes into account that the number of different products depends upon the different reagents, then it is clear that tannins are responsible for the complexity. Even if an HPLC method were able to separate each compound into discrete peaks, characterization would be a major problem. Another issue is that wine does not have a fbced composition. Differences are obvious from wine to wine, but also in the same wine as it ages. Another difficulty is the pH of the analysis. Most HPLC mediods used for pigment analysis need to maintain a mobile phase pH below 2. Therefore, large peaks may have little or no contribution at wine pH 20). 

The phenol composition of wine is considerably modified by barrel aging, thanks to controlled oxidation. Color is intensified due to reactions between tannins and anthocyanins, as well as others involving ethanal. The free anthocyanin concentration decreases and the tannin structure evolves, as does its reactivity to gelatin. After ten months of barrel aging, wines have better color than those aged in the vat (Table 13.8 Section... 

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