Exploring the effect of oxygen exposure during malolactic fermentation on red wine color

Abstract

AIM: this research investigates the impact of early oxygen exposure, also during malolactic fermentation (MLF), on pigments and color of a red wine from Sangiovese grapes.

METHODS: in order to tune up the oxidation-reduction potential right after maceration, a Sangiovese wine (ethanol: 13.5% v/v; pH: 3.73; total acidity: 7.4 g/L; volatile acidity: 0.38 g/L) was exposed to dose-controlled additions of oxygen (Ox) beginning at the draining off, during MLF, as long as 3 months over lees in a stainless steel tank. A control wine (no Ox) received no gas addition at all. Both wines were stored into the multifunctional tank Onda® (10 hL, Ghidi Metalli Srl) with automatic gas injection system. The main oenological parameters, phenolic compounds, and chromatic properties were investigated at: draining off, MLF, and 12 months of ageing (3 months over lees, 9 months in bottle).

RESULTS: as expected (Burns & Osborne 2013; Burns & Osborne 2015; Martínez-Pinilla et al., 2013), the decrease of total and monomeric anthocyanins occurred faster throughout the MLF and slowly during the further 12 months of ageing. The effect of oxygen exposure on both classes appeared significant only at the end of 3 months over lees, with lower anthocyanin levels in Ox wine (-10 mg/L). Regarding the contribution to the red color of wine, at the draining off it was mainly ascribable to the oligomeric (dAT 84%) and polymeric pigments (dTAT 10%). Thereafter, the molecular complexation of pigments increased the percentage of polymeric forms (35% at the end of MLF). However, only after 12 months of ageing, did the positive effect of the early oxygen exposure on red color stabilization become significant in terms of dTAT (65% Ox, 58% no Ox), dAT (30% Ox, 36% no Ox) and color intensity (0.50 Ox, 0.45 no Ox). 

CONCLUSIONS

Early oxygen exposure, useful for tuning up the oxidation-reduction potential right after maceration and during MLF, significantly improved the stability of pigments and color properties of Sangiovese red wine, from 12 months of ageing on.