Tannin evolution

Mouls, L. and Fulcrand, H. UPLC-ESI-Ms. 2012. Study of the oxidation markers released from tannin depolymerization Toward a better characterization of the Tannin evolution over food and beverage processing. Journal Mass Spectrom. 47 1450-1457. 

As a first approximation, this experiment represents the evolution of the coloring matter in red wines during aging. It confirms the large role of tannins in the color of old wines and thus shows that tannins play an important part in the color of young wines. Taken as another point, the possibility of a reaction between the anthocyanins and tannins already postulated (50) is accurately described. 

This reaction was confirmed in another experiment (17) using standard tests which followed the evolution of pigments in identical mixtures in tubes 1, 2, and 3 for two months. After allowing the tannins to react it appears that the anthocyanins contribute to the color of the solution to a limited extent. 

When the evolution of hydrogen sulfide ceases, the reaction vessel is opened and the brownish yellow, powdery material is transferred to a large porcelain dish and mixed with 3 liters water to dissolve out the salt. The dye is then filtered off and dissolved in about 1500 cc. water at 60°C. Higher temperatures should not be employed because aura-mine is easily decomposed. The solution is filtered to remove a small residue of sulfur and Michler ketone, and is then mixed with 1 liter of the salt solution obtained as the preceding filtrate. The auramine precipitates as lustrous golden plates. The yield of pure dye is about 155 grams. It gives pure yellow shades on cotton mordanted with tannin and tartar emetic. 

In this paper, we focus our attention to the effect of tannin on wine color by the two types of phenomenon Copigmentation and reactions with anthocyanins in relation to the initial color of wine and its evolution. 

Table 6.8. Comparison of evolutions in the results of tannin assays in wine aged under different conditions for 15 months (a, b and c are oak barrels of different origins) (Glories, 1992, unpublished)...

In practice, these various conditions must be taken into account in aging red wines, and modulated according to the type of wine. Aeration is desirable at the beginning, to degas the wine and promote the stable, purplish-colored combinations with ethanal that develop from only slightly polymerized tannins. Aeration should then be reduced to maintain a high oxidation-reduction potential, as this is favorable to the evolution of tannins. Aeration should... 

Okuda T, Yoshida T, Hatano T (2000) Correlation of oxidative transformations of hydrolyzable tannins and plant evolution. Phytochemistry 55 513-529... 

Fig. 10.12. Evolution of phenolic compounds (Darnd, 1991) (results expressed in mg/g dry weight) , skin anthocyanins , skin tannins , seed tannins...

Evidently, these notions pertaining to the evolution of color and anthocyanins in terms of maceration time primarily concern new wines—anthocyanins are in fact the essential elements of their color. As wine matures, the role of tannins becomes increasingly important. Extended vatting times produce more colored wines, even if the resulting new wines initially appear to confirm the contrary. 

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