In berry distribution and extraction of thiol precursors in Gewürztraminer.

The so-called varietal thiols are an interesting technological class of compounds that contributes to the "tropical" notes of wine. The factors governing the formation of their precursors and the conversion to the corresponding free forms are still discussed (Thibon et al. 2016) but, technologically speaking, the precursor availability is a prerequisite. Several data are present in the literature regarding Sauvignon Blanc (SB), while fewer deal with Gewürztraminer (GWT; Dubordieu and Tominaga 2009; Roland 2010a & b; Concejero et al., 2014), a variety native to Tramin, in South-Tyrol (Italy). For this reason, we investigated the concentration of 3-S-glutathionylhexan-1-ol (GSH-3MH) and 3-S-cysteinylhexan-1-ol (Cys-3MH) in GWT as regards: (1) the distribution between marks and juice in samples processed at a semi-industrial scale, in comparison with SB samples having similar °Brix and pressing yield; (2) the effect of pre-fermentation skin-contact protocols, also used along with commercial enzymes to favour extractions from skin; (3) the fractioning during pressing on industrial-scale. Thiol precursors were analysed according to Larcher et al. (2013). GWT skins are characterised by a higher content in precursors compared to SB’s at the same pressing yield, while this difference is turned upside down in juice. Pre-fermentation skin-contact significantly increased thiol precursors' concentration while the impact of the enzymes was not significant. Around 30% of total precursors are contained in the pressing fraction corresponding to the final 5% of the juice.