Controlling the redox potential in red wines through cap management and mixing techniques

Petite Sirah wines were produced using five cap management protocols, including punch-downs (PD); pump-overs (PO); 1 h air mixings (AirMix); 1 h nitrogen mixings (N₂Mix); and air injections triggered by oxidation-reduction potential (ORP) of ≤-40 mV (RedoxConAir). ORP, reduced glutathione (GSH), and glutathione disulfide (GSSG) were monitored throughout fermentation. During cap management, AirMix and PO wines increased ORP by ≥250 and ≥100 mV respectively, whereas PD wines increased ORP 20 to 40 mV. N₂Mix and AirMix wines showed a GSH:GSSG ratio of 5:1 and of 1:5, evidencing respectively reductive and oxidative fermentations. AirMix wines contained 30 % less phenolics than PD wines. Isoamyl acetate showed odor activity values (OAV) ranging from 248 in RedoxConAir wines to 120 in AirMix wines. RedoxConAir wines showed 27 % greater concentrations of volatiles than PD wines. GSH and GSSG were identified as markers for the redox trajectory of wines during alcoholic fermentation.