Red wine color: the role of polymeric pigments and pyranoanthocyanins in SO2 bleachable methods

In this work, copigmentation assay described by Boulton and the “chemical age” indices proposed by Somers and Evans in wine were critically reviewed and updated. In particular, the influence of polymeric pigments and pyranoanthocyanins on color is reassessed. The current analytical understanding of these pigments should be taken into account when applying both methods, as some implicit considerations about SO2 bleaching are presumably affected by their chemical structure. The differences between Anthocyanin-Tannin (AT) and Tannin-Anthocyanin (TA) polymeric pigments are carefully described, as well as the importance of pyranoanthocyanin contribution to the color. As a result, and considering current scientific knowledge, the true meanings of terms such as polymeric pigments and free anthocyanins in both analytical methods have been reviewed. Some possible research lines to improve these reliable and fast methods have been proposed.