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

Area of Science:

• Enology
• Wine Chemistry
• Fermentation Science

Background:

• Cap management is crucial in red winemaking, influencing extraction and fermentation.
• Oxidation-reduction potential (ORP) and glutathione (GSH/GSSG) are key indicators of wine fermentation dynamics.

Purpose of the Study:

• To investigate the effects of five distinct cap management protocols on Petite Sirah wine fermentation.
• To analyze the impact of these protocols on ORP, glutathione status, phenolics, and volatile compounds.

Main Methods:

• Petite Sirah wines were fermented using punch-downs (PD), pump-overs (PO), air mixing (AirMix), nitrogen mixing (N₂Mix), and ORP-controlled air injection (RedoxConAir).
• ORP, reduced glutathione (GSH), and glutathione disulfide (GSSG) were monitored throughout fermentation.
• Phenolic content and key volatile compounds, such as isoamyl acetate, were analyzed.

Main Results:

• AirMix and PO significantly increased ORP, while PD had a minor effect.
• N₂Mix resulted in a reductive fermentation (GSH:GSSG ratio 5:1), whereas AirMix indicated an oxidative fermentation (GSH:GSSG ratio 1:5).
• AirMix wines had 30% less phenolics than PD wines; RedoxConAir wines showed 27% higher volatile concentrations than PD wines.

Conclusions:

• Cap management protocols distinctly alter the redox conditions during Petite Sirah fermentation.
• GSH and GSSG serve as reliable markers for tracking the redox trajectory of wines.
• Specific protocols like AirMix and RedoxConAir can modulate phenolic and volatile profiles, impacting wine style.