Pre-fermentative supplementation with grape tannin can give an extra amount of 3-mercatpohexanol and its acetate in wine

Tannins are widely used in winemaking (classified by the International Organisation of Vine and Wine as clarification agents for protein stabilisation of musts and wines; COEI-1-TANINS: 2009) and for food and beverage production (recognised by the European Commission as flavourings and food ingredients; EC No 1334/2008, EU Regulation No. 872/12). Recently, for the first time relevant amount of the S-glutathionylated and S-cysteinylated precursors (GSH-3MH and Cys-3MH) of 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) have been identified in commercial grape tannins (Larcher et al., 2013). This evidence suggested new opportunities of technological use of these adjuvants for improving the exotic-fruit flavour profile of wine after fermentation. This hypothesis was experimentally investigated fermenting 17 Mueller Thurgau (MT) and 15 Sauvignon Blanc (SB) grapes according to 2 lab-scale distinct protocols: TAN and REF (respectively, with and without addition in the juice of a selected grape tannin particularly rich in GSH-3MH and Cys-3MH). Wines obtained from must added of grape tannin were significantly richer in the total content of the 2 thiols (expressed as sum of the molar concentrations; Tukey’s test, p < 0.001) with median contents of 12.6 nmol/L in TAN vs. 5.16 nmol/L in REF for MT, and 11.3 nmol/L vs. 2.69 nmol/L for SB wines. The addition of precursors rich tannin produced wines with increased free thiols contents. The concentration of 3MH in MT (Tukey’s test; p < 0.001) and in SB (p < 0.001), and that of 3MHA in MT (p < 0.001) and in SB (p < 0.05) was significantly higher in the TAN wines. Conversion yields and absolute concentrations of the free thiols seem to support this hypothesis and are in agreement with those reported in the literature for these precursors (for MT was 1.85% and 1.37% and for SB 0.36% and 0.85%, for REF and TAN samples, respectively)