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

Abstract

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.

Fermentative and post‐fermentative oxygenation of Corvina red wine: influence on phenolic and volatile composition, colour and wine oxidative response

“…Enzymatic oxidation almost entirely occurs in grape musts, due to the presence of grape enzymes such as polyphenol oxidases . Chemical oxidation is dominant during wine aging, and it is generally accepted that in the production of red wine, a mild oxidation after fermentation can improve red wine aroma, colour stability and mouthfeel . Key steps for oxygen supply of red wine have been shown to be barrel aging, micro‐oxygenation or bottle aging .…”

“…Key steps for oxygen supply of red wine have been shown to be barrel aging, micro‐oxygenation or bottle aging . However, excessive oxygen exposure after fermentation can also produce undesirable and unpredictable effects such as the formation of off‐flavours and the loss of colour …”

“…It is known that fermentation of musts in anaerobic condition can help increase yeast production of various esters contributing to wine fruity aromas in white wines . In red wine, it has also been shown that oxygen supply during fermentation can decrease the final concentration of certain volatile sulfur compounds …”

“…2,13,14 However, excessive oxygen exposure after fermentation can also produce undesirable and unpredictable effects such as the formation of off-flavours and the loss of colour. 6,8,15,16 In addition to contributing to various oxidation mechanisms, oxygen availability is also central to yeast metabolism. Some studies have evaluated the impact of dissolved oxygen during alcoholic fermentation demonstrating the positive influence of oxygen addition on yeast physiology, in particular with regard to fermentation rate and efficient membrane lipid biosynthesis, the latter positively impacting cell viability and ethanol tolerance.…”

“…[19][20][21] In red wine, it has also been shown that oxygen supply during fermentation can decrease the final concentration of certain volatile sulfur compounds. 6 In addition, it has to be considered that, regardless of the stage of winemaking at which it occurs, oxidation inevitably induces a depletion of wine oxidizable substrates. 2 Accordingly, wines that have been exposed to oxygen earlier in their life, for example during the maceration stages, could have different ability to react with oxygen later in their life, which might have important implications in terms of wine longevity.…”