Wines produces without SO2 addition: which impact on their colour? An approach at the global and pigments levels

Abstract

Since the 18th century, sulfur dioxide (SO2) is used in winemaking. Added at different steps, its antimicrobial but also antioxidasic and antioxidant properties are very helpful for winemakers. Nevertheless sulfur dioxide has a real potential health impact, particularly for sensitive consumers often highlighted by hygienists. Nowadays, a serious trend for “natural” wines (i.e. produced without any additives), as described by their producers, could be observed on the French market what match with a proliferation of wines elaborated without any sulfite addition. 

During the winemaking process, anthocyanins are extracted from the grape’s skins and their concentrations and chemical reactivity all over red wine shelf life will determine its colour. If the key role of oxygen during ageing on colour stabilization is well established for a long time and explained by the production of acetaldehyde (from ethanol) which allow to create ethylidene bridges between anthocyanins and tannins (Es-Safi, 1999. Recently a strategy has been develop to identified and quantified separately each family of polymeric pigments formed during ageing in red wine by UPLC-UV-Q-TOF (Zeng, 2015)

Wines selected for this study were, on one hand, thirty-five commercial wines from Bordeaux area (2015 and 2016 vintages, respectively 19 produced without sulfite addition and 16 with) and, on the other hand, eight experimental wines also produced with and without sulfites addition from grapes of the same plot a different maturity levels (2017 and 2018 vintage). Wines were analyzed by spectrophotometric techniques and their polymeric pigments were quantified by UPLC-UV-Q-TOF. Colour of wines produced without sulfites addition were more intense and L*a*b values indicated that they significantly had deeper purplish colour than the wine with sulphite. This colour differences indicating a more qualitative stabilisation of the red wine colour. The quantification of each polymeric pigments by UPLC-UV-Q-TOF after acidic depolymerisation shows that polymeric pigments with an ethylidene linkages between the anthocyanins moieties and the flavanol moieties were significantly more abundant in the red wine produce without sulphite. This higher concentration of these polymeric pigments could explain the observed colour differences since they are known to exhibit a purple colour.