Oxidative vs reductive skin maceration on thiol precursors

Grape maceration and skin contact is one of the first steps in winemaking and it can condition wine aroma profile and flavour. Several studies have shown how the oxidative maceration occurring in machine harvested grape [1,2] can increase the level of thiol precursors and relevant free thiols. This latter even is particularly important due the extremely high impact these molecules on final wine aroma. Believing that machine harvest alone could be the Holy Grail of thiol production could underestimate the complexity of the pathways available and the lack of knowledge about where these molecules are originating from (only few % of the known pathways are explaining the free thiols found in wine). This communication wanted to explore to a closer detail on a larger scale the effect of maceration on the production of two known precursors (S-3-glutathionyl hexan1-ol and S-3-cysteinyl hexan-1-ol) [3]. 19 Mueller Thurgau and 32 Sauvignon blanc were considered and results seemed to be a bit more complex than what was envisaged in the literature. Increases of the two precursors were observed only in some sample (not all of them as other found), highlighting how the simple oxidation mechanism might not explain completely the de novo formation of thiol precursors in all grape/wine samples