Grape pigment phenomena: Interpretation of major colour losses during vinification

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Abstract
Large decreases in colour density during the making of red wines, whether by the traditional fermentation on skins or by thermovinification, have not previously been explained in terms of juice and wine composition. The major colour loss is actually due to the extreme instability of deeply coloured pigment structures initially present in the juice extract to ethanol, whereas decrease in anthocyanin content is a minor contributing factor. The consequent decline in colour density during fermentation can be as much as five‐fold under conditions of high pH. Both red and blue chromophoric forms of the anthocyanins, in self‐association and co‐pigmentation with related flavonoid phenolics, are proposed as being present in the juice pigments. The stability of such complexes is ascribed to intermolecular hydrogen bonding forces. The existence of two nearly distinct phases in the accounting of total phenolics during ‘evolution ’of a red wine is emphasised.