Effect of oxygen exposure during fermentation on volatile sulfur compounds in Shiraz wine and a comparison of strategies for remediation of reductive character

Background and Aims: Oxygen (O₂) plays a fundamental role in the establishment of wine style and aroma. The effect of O₂ treatment during fermentation on the formation of volatile sulfur compounds (VSCs) and the subsequent impact on the sensory profile of wine was investigated. Traditional VSC remediation strategies were also evaluated. Methods and Results: Shiraz wines were treated with O₂ at several levels during fermentation by sparging rotary fermenters with three types of gas mixtures (40% O₂, 21% O₂ and N₂). The controls were not sparged with any gas and were subsequently subjected to three remedial treatments (aerative racking, early- and late-Cu²⁺ addition). Wines were analysed for VSCs, fermentation products, concentration of residual metals, as well as their sensory profile. Non-oxygenated ferments and wines contained a higher concentration of VSCs and a lower concentration of fermentation products and differences in the concentration of metals. Volatile sulfur compounds responsive to O₂ treatment were identified and a relationship between O₂ dose and concentration on VSC formation was demonstrated. The 'early-Cu²⁺ addition' remediation strategy proved the most effective in reducing the impact of 'reductive' aromas in non-oxygenated wines. Conclusions: The risk of producing a wine with high VSC concentration that negatively impacts wine aroma as well as with a low concentration of fermentation products associated with positive red fruit aromas was decreased by treating wines with O₂ during fermentation. Significance of the Study: This work specifically examines important aspects of O₂ treatment during fermentation in relation to 'reductive' aroma characters and the overall impact on the wine's sensory attributes.