Spectral evaluation of young red wines: Anthocyanin equilibria, total phenolics, free and molecular SO₂, “chemical age”

TLDR

Red wine colour results from monomeric anthocyanins and polymeric pigment forms, whose differing responses to pH and SO₂ enable routine estimation of anthocyanin equilibria that have shown correlations with wine quality. The study models these equilibria with two percentage parameters α and α′ linked to wine pH and added SO₂, deriving free and molecular SO₂, anthocyanin content, and total phenolics from spectral data under a set of analytical approximations. Comparative evaluations confirm the validity of these approximations across a wide range of vintage wines, and the work presents ageing changes in colour composition alongside spectral indices of “chemical age.”.

Abstract

Abstract Red wine colour is an integration of contributions from monomeric anthocyanins and polymeric pigment forms. Because of gross differences between the two fractions in their responses to pH change and to SO 2 addition, approximate measures of the states of anthocyanin equilibria in young red wines can be routinely made. Recent correlations of such measures with independent assessments of relative wine quality have prompted further examination and development of the original analytical concepts. The equilibria may be described in terms of two percentage parameters α and α ', the values of which are related to wine pH and to SO 2 added after fermentation. Measures of free SO 2 and also molecular SO 2 , anthocyanin content and total phenolics are obtained from the same set of spectral data. The interpretations are based upon a number of analytical premises for which certain approximations have been necessary. These appear to be well justified in comparative evaluations because of the wide range of parameter values observed in surveys of current vintage wines. Observations of ageing changes in the composition of wine colour, with proposed spectral indices of “chemical age”, are also presented.