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Oenological tannins in combination with bioprotectors could become a sulphur alternative in rosé wines, according to a trial in Burgundy. University lecturer Maëlys Puyo tested this possibility at the University of Burgundy in Dijon for her doctoral thesis. She explains her approach: "Bioprotection prevents the growth of the grape's own flora, but has only a minor effect against oxidation. It can therefore not replace sulphur dioxide (SO2). Tannins, on the other hand, have antioxidant properties. They could be an interesting alternative to SO2 to protect the musts from oxidation and thus from the fading of the wine colour."
Puyo added 10 g/hl of Primaflora bioprotective yeast to Pinot Noir grapes in the press. After pressing, she distributed the must into different tanks: two exclusively bioprotected control tanks, two tanks with 5 g/hl gallic acid tannins, two tanks with 15 g/hl quebracho tannins and two tanks sulphurised with 5 g/hl SO2. After fermentation, the wines were bottled directly with 3 g/hl SO2 and then stored in a dark cellar for 15 months. The permitted limits for rosé wines are around ten times the amount of sulphur used here.
Chemical analyses of anthocyanins and phenolic compounds as well as colourimetric measurements showed, as expected, that bioprotection alone did not protect against oxidation. However, the addition of oenological tannins in combination with bioprotection stabilised the colour of the rosé just as well as the addition of SO2. The quebracho tannins proved to be more effective than the gallic acid tannins. Sensory tests showed that the tannins did not affect the flavour or the perception of the wine's astringency. "At the doses used, the wines with oenological tannins are neither more astringent nor more bitter than the sulphurised wine. We also did not observe any significant differences in the 'intensity of fruitiness' parameter," says Puyo. However, further research is still needed: "It remains to be seen how this strategy will affect other grape varieties, vintages and tannins on a larger scale.".
(al / vitisphere)