The use of commercial grape tannins can increase the 3-mercaptohexanol precursors in juice and affect the tropical fruity characteristics of wine

The so-called varietal thiol precursors 3-S-cysteinyl- and 3-S-glutathionyl-hexan-1-ol (Cys-3MH and GSH-3MH, respectively) were recently found for the first time in some commercial grape tannins (Larcher et al. 2013). The capacity of these additives or clarifying agents for increasing the thiol aroma of wine has been observed in lab scale (Larcher et al. 2014). In this paper we give further evidence of the possibility of enhancing the tropical and grapefruit¬-like aroma as well as the pleasantness of Aromatic Traminer (TR) and Sauvignon Blanc (SB) wines produced in semi-industrial scale. SB (n=3) and TR (n=3) juices were spiked with a grape tannin (500 mg/L) rich of precursors (Cys-3MH, 125 mg/kg; GSH-3MH, 162 mg/kg), and fermented in comparison with the same juices spiked with a grape tannin (500 mg/L) poor of precursors (Cys-3MH, 0.1 mg/kg; GSH-3MH, 0.3 mg/kg) and with control juices where no tannins were added. Fermentations were carried out at 18-20°C by 2 yeast strains (Vin13 and VL3, 300 mg/L) having lyase activity on the thiol precursors. Argon blanketing was used after inoculum at any winemaking step to prevent oxidation. Sensory analysis was performed by minimum 17 expert judges. The orthonasal olfaction of the sulfited, devatted and cold stabilised wines proved that only the addition of the tannin rich of thiol precursors significantly (p<0.05) increases - both in SB and in TR - the perception of a tropical, grapefruit-like aroma as a consequence of the release of 3-mercaptohexanol and the possible formation of its acetate. This "new" aroma did not penalize the pleasantness and typicality of TR wine aroma. When added at the end of fermentation, the rich tannin was ineffective. No differences were olfactorily perceived between yeast strains as regarded the thiol related aroma