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.

Undesirable volatile sulfur compounds with aromas, such as boiled or rotten egg, sewage and rubber, can impact negatively on wine sensory attributes. The identity of these molecules is known but knowledge gaps exist about their source and ways to manage them in winemaking. This review focuses on the chemistry of the three main compounds: hydrogen sulfide, methanethiol and dimethylsulfide. Discussion centres on their possible origins and the efficacy of methods currently used to control them during wine production. The role of metals, both in the vineyard and in the winery, in the formation and release of these three volatile sulfur compounds is described. Oxygen management during fermentation and bulk ageing is discussed along with the impact of the bottle closure.

Diorganopolysulfanes can be generated when hydrogen sulfide (H2S) and thiols are oxidized in the presence of Cu­(II) under conditions usually aimed at removing H2S from wine. This work sought to understand if polysulfanes could act as latent sources of H2S during postbottling storage. The stability of the polysulfanes formed in situ in model wine containing cysteine, H2S, and transition metals was dependent both on the number of sulfur linking atoms (Sn) and on the presence of a reducing agent, such as sulfur dioxide or ascorbic acid. A polysulfane containing three linking sulfur atoms was the most stable, with 84% of the relative initial amount remaining in solution after six months, compared to polysulfanes containing four or more linking sulfur atoms that decomposed rapidly, with 26% remaining after six months. Importantly, sulfur dioxide was associated with the rapid degradation of polysulfanes and subsequent liberation of H2S. Three cysteine-S-sulfonates were also tentatively identified, which gives insight into the possible release mechanisms involved with H2S reappearance.

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Abstract:The combined synergistic effects of copper (Cu 2+ ) and sulfur dioxide (SO 2 ) on the formation of hydrogen sulfide (H 2 S) in Verdelho and Shiraz wine samples post-bottling was studied over a 12-month period. The combined treatment of Cu 2+ and SO 2 significantly increased H 2 S formation in Verdelho wines samples that were not previously treated with either Cu 2+ or SO 2 . The formation of H 2 S produced through Cu 2+ mediated reactions was likely either: (a) directly through the interaction of SO 2 with either Cu 2+ or H 2 S; or (b) indirectly through the interaction of SO 2 with other wine matrix compounds. To gain better understanding of the mechanisms responsible for the significant increases in H 2 S concentration in the Verdelho samples, the interaction between Cu 2+ and SO 2 was studied in a model wine matrix with and without the presence of a representative thiol quenching compound (4-methylbenzoquinone, 4MBQ). In these model studies, the importance of naturally occurring wine compounds and wine additives, such as quinones, SO 2 , and metal ions, in modulating the formation of H 2 S post-bottling was demonstrated. When present in equimolar concentrations a 1:1 ratio of H 2 S-and SO 2 -catechol adducts were produced. At wine relevant concentrations, however, only SO 2 -adducts were produced, reinforcing that the competition reactions of sulfur nucleophiles, such as H 2 S and SO 2 , with wine matrix compounds play a critical role in modulating final H 2 S concentrations in wines.

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Background and Aims: Winemakers utilise various remediation strategies for decreasing 'reductive' characters in wine. Remediation strategies, such as the addition of diammonium phosphate (DAP) during fermentation, copper fining, the addition of fresh lees or lees products to wine, and aeration of the must during and after fermentation, are commonly employed in an effort to prevent the formation or to remove undesirable volatile sulfur compounds. In this study, the relative effectiveness of five strategies for remediation of 'reductive' aroma was compared in a Shiraz wine. Methods and Results: At the onset of the development of 'reductive' aromas during Shiraz fermentation, each ferment was treated with a unique remediation strategy: DAP addition; macro-oxygenation; copper fining; a combination of macrooxygenation and copper fining; or the addition of fresh lees from a donor wine. While a relatively small difference in volatile sulfur compounds was found between treatments, copper fining, lees and DAP addition produced wines with elevated 'reductive' characters at certain time-points post-bottling; while macro-oxygenation or macro-oxygenation with copper produced wines with a low sensory score for 'reduction'-related attributes. Conclusions: Macro-oxygenation during fermentation was the most effective remediation strategy. Lees addition, and to a lesser extent, copper fining and DAP addition, diminished fruit attributes and produced wines with noticeable 'reductive' characters. Significance of the Study: Macro-oxygenation during fermentation produced wines with the lowest 'reduction'-related attributes while enhancing 'fruity' attributes. This work also highlighted the compositional effects of each type of remediation treatment.