Anthocyanins in Tannat wines rapidly evolve toward unidentified red-coloured pigments

AIM: To assess the relationship between the reported low-stability of Tannat colour during wine storage and its pigment composition and evolution

METHODS: Twenty wines were elaborated under experimental conditions over two vintages, 2015 and 2016, eight corresponding to Tannat, and six to Syrah and Marselan. Wines were stored in darkness under cellar temperature conditions. Anthocyanins and tannins were quantified by spectrophotometric methods as well as by HPLC-DAD-ESI-MSn. Analysis were made three months after the end of winemaking, and twelve and twenty-four months later.

RESULTS: At three months, the pigment content determined by HPLC (spectrophotometer) ranged between 190-240 mg/L (370-665 mg/L) in Tannat, 200-320 mg/L (420-470) in Marselan and 100-305 (220-340) in Syrah. Colour intensity was between 17-28 AU in Tannat, 15-17 in Marselan and 10-16 in Syrah. From the second analytical date on, Tannat wines registered the lowest HPLC/spectrophotometer anthocyanin quotient, tendency increasing with wine age. Besides, Tannat wines presented much higher decreases of the HPLC anthocyanin content between analytical dates than the observed in Marselan and Syrah. This was independent from the type of pigment considered. Moreover, the unresolved HPLC broad peak was also of a higher relative magnitude in Tannat wines. This could not be explained by the tannin contents or pH measured in the wines. Spectrophotometric anthocyanin results did not show such differences among cultivars, neither in the proportion of SO2 bleachable pigments. Tannat wines showed as well the highest colour intensity decreases through time.

CONCLUSIONS: The result suggests that in Tannat wines, anthocyanins may evolve rapidly towards polymeric pigments that would still have red-bluish hues but would be less stable. These findings could be behind the low colour stability reported in literature for Tannat wines, and could be a starting point for future research.