The synergistic effects of Cu, Fe, Mn, Zn, and Al on the evolution of different volatile sulfur compounds (VSCs) in a Chardonnay and a Shiraz wine have been investigated. The evolution of H2S, MeSH, and DMS were influenced by metal addition, and in some instances, a combination of metals was responsible for the largest variation in the concentration of VSCs. The metals and metal combinations associated with significant changes in VSC concentrations in both Chardonnay and Shiraz samples after anaerobic storage were Cu, Fe, Zn, Al, Cu*Fe, Cu*Mn*Al, and Cu*Zn*Al for H2S; Cu, Zn, Fe*Mn, and Cu*Fe*Mn for MeSH; and Al and Zn*Al for DMS. The effect of Cu addition on the evolution of VSCs has previously been shown; however, this investigation has demonstrated that metals other than Cu could also be involved in the catalytic release of VSCs and that the interactions and combinations of metals are important. In some instances, the metal effect was reversed, associated with significant decreases during high oxygen conditions and with significant increases during low oxygen conditions.

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.

Copper is one element in wine that has considerable notoriety. While current winemaking practice tends to minimise the amount of copper that results from vineyard and winery sources, the addition of copper(II), either as its sulfate or citrate, to remove sulfidic off-odours may result in an elevated concentration in the finished (bottled) wine. Residual copper in white wine has been linked to oxidative and reductive spoilage processes, although the mechanisms are at times speculative. The presence of copper has been implicated in haze formation (copper casse) and linked to protein instability. More recent concerns include the coexistence of residual copper and hydrogen sulfide in wine stored under low oxygen conditions. The chemistry of copper is important in both white and red wine. While there are some overlapping issues, especially with respect to sulfidic off-odours, both white and red wine display their own unique chemistry. Thus, this review describes the state of knowledge of copper in white wine, differentiating between evidence-based claims and speculation. It also identifies areas of research that will provide a much clearer understanding of the role of copper in wine spoilage.

Temperature can play a significant role in the development of wine at many stages during its lifetime. Elevated temperature, however, poses a significant risk to the sensory attributes of wine and its resultant shelf-life. Wines often experience difficult environmental conditions during transport and storage, and this can directly impact on the colour, aroma and mouthfeel of the wine. Higher and/or fluctuating temperature can essentially accelerate the ageing process. Unfortunately, these changes often go unnoticed until the wine reaches the consumer. Numerous studies have investigated the impact of elevated temperature on wines, with noticeable effect, such as reduction of sulfur dioxide, colour development (especially browning of white wines) and changes in the profile of volatile compounds, being common. Unfortunately, most of these studies tend to have a narrow scope and tend to focus only on a limited number of wine types or on specific compounds. The chemistry changes involved in heat-affected red wines are generally more complex than they are in white wines, but it is arguable that white wines are more sensitive to the effect of heat and therefore require the same or a greater level of research consideration with respect to temperature effects. The focus of this review is to highlight the common effects that different wine types and styles can experience when subjected to elevated storage temperature that are considered to be beyond the limits that most winemakers and consumers would accept. This review will also summarise the fundamental chemical kinetics that play a significant role in wine development at elevated temperature.

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.