Color due to copigmentation

Levengood, J., Boulton, R. (2004). The variation in the color due to copigmentation in young Cabernet Sauvignon wines. In A. L. Waterhouse J. A. Kennedy (Eds.), Red wine color revealing the mysteries (pp. 35-52). Washington DC American Chemical Society. 

The Variation in the Color Due to Copigmentation in Young Cabernet Sauvignon Wines... 

The method used to measure the amount of the copigment complex in a red wine, and the other measures, is referred to as the copigmentation assay. This method measures the absorbance of a sample altered by dilution together with those resulting from additions of acetaldehyde or sulfur dioxide (7, 8). The procedure differs from previous methods in that all readings are made at a standardized pH (3.6) and at 12% ethanol and makes no assumptions about the extinction coefficients, ionization or the color shifts. It also subtracts the color due to copigmentation from wine color in order to make the anthocyanin estimate. 

Color due to Copigmentation (AU) Color due to Anthocyanins (AU) Color due to Polymeric Pigment (AU) Correlations... 

The range, mean, standard deviation and coefficient of variation of each component of the wine color, across all wines are shown in Table I. It can be seen that there is at least a two-fold variation within these wines in all color components. In the cases of the color due to copigmentation and the polymeric pigment, this variation is three-fold. 

Mean and Variation of Color Due to Copigmentation Cabernet Sauvignon Wines, 1995, Napa Valley... 

Figure 2. The distribution of color due to copigmentation by wineryand across...

The range of the color due to copigmentation was from 1.8 to 5.7 with a mean of 3.3 and a coefficient of variation of 28%. This variation is the highest of all the color measures, considerably more variation than the anthocyanin content and this must be due to the variation between the wines in their cofactor content. This wide variation within wines of a single cultivar and region would have been underestimated if the traditional measures of color had been used. 

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.

Principal Component Analysis (PCA) and Partial Least squares (PLS) regression were used to investigate relationships that might exist between various vineyard and winemaking practices and the 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. 

Figure 4. The correlation of color due to copigmentation with all variables.

Figure 6, shows the simple regression between the crop (as pounds per vine) and the color due to copigmentation. The crop level alone accounts for 57% of the variation with a significant offset. Note that the correlation does not mean that higher crop loads lead to higher color. 

The extent to which the winemaking measures can account for the variation in color due to copigmentation is shown in Figure 8. Together they are responsible for only 34% of the variation in the color due to copigmentation... 

The primary conclusion reached in this research is that none of the viticultural or enological ctors examined affected the color due to copigmentation of the anthocyanins. 

The conclusion reached in the evaluation of relationships between the color due to copigmentation and various viticultural and enological fectors was, under this set of experimental conditions, that no significant relationships exist... 

Figure 5. The prediction of color due to copigmentation from all vineyard...

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