Wine color correlations

The anthocyanin is malvidin-3,5-diglucoside (Fluka), and the tannins are a sample of leucoanthocyanins extracted from the bark of the maritime pine (Pinus pinaster). The products are not identical to the natural grape pigments nevertheless, it may be assumed that the observed facts correlate, as a first approximation, with red wine color and its changes. 

The correlation of wine color with the anthocyanin color, the color due to copigmentation and the color of the polymeric pigments, individually, are straight-line relationships. More important is the fact that a higher correlation exists for the color contribution of the copigment complex, (R = 0.77), Figure 3, than for the color due to anthocyanins (R = 0.57) or polymeric pigments (R = 0.66), data not shown. 

Figure 3. Correlation between wine color and color due to copigmentation.

Prediction functions, based on the principal components, were used to see how much of the variation in the copigmentation measures could be accounted for by the vineyard and winery practices, using PLS methodologies. When all of the vineyard measures and winery conditions were included, 66% of the variation could be accounted for. The predicted color due to copigmentation is plotted against the actual values in Figure 4. Four components were used and the correlation coefficient is 0.82.Note that wine number 50 seems to be an outlier in this correlation. 

The wine was a Syrah obtained soon after pressing and we could attribute over 30 percent of the total color at pH 4.9 to polymeric pigments that did not precipitate with protein. When the wines shown in Figure 2 were re-examined and the amount of LPP and SPP were added together, the correlation with polymeric pigments by the Somers assay was found to be quite good (Figure 4). 

There are number of chemical methods for the determination of the total anthocyanin content in a wine, the most simple being variations in the color of a wine as a function of pFl. At very acidic pFl, ant-hocyanins are in their flavinium cation form, whereas under mildly acidic conditions the carbinol pseudobase (Figure 3) is formed. The absorbance of the wine is read at pH 0.6 and at pH 3.5 and the difference in absorbance has been empirically shown to correlate with the anthocyanin concentration. Anthocyanin determination using the difference in absorbance before and after the addition of a known quantity of sulfur dioxide is based on the same principle. 

In the red wines the tannin content was not correlated with the color. The permanganate index, for example, varied from 4.7 to 12.9 with colors of 41 to 330. Rib4reau-Gayon and Maurie (1942) reported that wines with a high permanganate/ color ratio were more astringent than those with a low ratio. 

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