Factors affecting the formation of red wine pigments

Abstract

The development of pigments during red wine fermentation has been shown to proceed by the conversion of the relatively unstable grape-derived anthocyanins to more complex and color stable pigments through the formation of both ethyl-linked and vitisin-like pigments. These ethyl-linked pigments are more resistant to hydration and bisulfite bleaching than the parent anthocyanins, a phenomena explained by steric hindrance to nucleophilic attack and by alteration of the electronic properties of the anthocyanin entity. Furthermore, they have been shown to be formed rapidly during fermentation and likely to consume much of the anthocyanins extracted from the grapes. Because they are purple in color it is suggested that the purple hues of young red wines, particularly immediately after the completion of fermention, are a result of the high concentrations of these pigments. The ethyl-linked pigments are degraded quickly with time, however, and may provide a pool of reactive intermediates in the formation of more stable red wine pigments. The vitisin-like compounds, on the other hand, are long lived and have been shown to persist in red wine over many decades. Whilst the reaction to produce the ethyl-linked pigments requires the loss of a proton in the reaction sequence, the production of the vitisin-type compounds depends on an oxidation step. The presence of atmospheric oxygen has been shown to be necessary for the formation of vitisin A in model systems but in red wine ferments the rate of vitisin A synthesis may be correlated with active oxidants rather than just oxygen concentration. © 2004 American Chemical Society.