Copper(II) and Sulfur Dioxide in Chardonnay Juice and Shiraz Must: Impact on Volatile Aroma Compounds and Cu Forms in Wine  
[PERSON]  
1 National Wine and Grape Industry Centre, Wagga Wagga, NSW 2678, Australia; [EMAIL_ADDRESS] (N.  
compounds are prone to nucleophilic attack by hydrogen sulfite (HSO\({}_{3}\)-, an equilibrium form of SO\({}_{2}\)) and hence readily form addition products that are odorless (non-volatile) [10; 11; 12]. However, as SO\({}_{2}\) can be gradually depleted during aging [13; 14], the addition products can progressively dissociate and release free aldehyde compounds [15; 16] and the accompanying off-flavors.  
In contrast to the aldehyde compounds, low molecular weight sulfur compounds (LMWSCs) can contribute significant'reductive' off-flavors to wine [17]. Sulfur-containing pesticides [18] and gaseous sulfur dioxide (SO\({}_{2}\)) or potassium metabisulfite (PMS) [17] added after harvest are potential precursors for LMWSCs. Grape juice with high turbidity [19] and/or a lack of sufficient oxygen [20] and nitrogen [18; 19; 21; 22] supply during fermentation also facilitates the production of these compounds. For example, hydrogen sulfide (H\({}_{2}\)S), a detrimental LMWSC in wine, can be generated by _S. cerevisiae_ from elemental sulfur, sulfate, or sulfite [3; 22; 23] through the sulfate assimilation and reduction pathway [24]. Sufficient nitrogen and oxygen supply during fermentation can promote the yeast sulfide assimilation and thereby reduce H\({}_{2}\)S concentration in the finished wine [20]. Other LMWSCs are also produced through yeast metabolism [3; 18; 24], such as methanethiol (MeSH) [17; 25; 26] and dimethyl sulfide (DMS) [27; 28; 29]. Conventional wine production procedures utilized to remove LMWSCs include aeration, copper fining, and the addition of yeast lees [23; 30]. In terms of copper fining, H\({}_{2}\)S can readily form copper(I) sulfide (Cu\({}_{2}\)S) upon reaction with Cu(II) in model wines [31]. Although the Cu\({}_{2}\)S is involatile, the particles formed are approximately 0.1-0.2 \(\upmu\)m in diameter, do not readily settle, and are not readily removed via filtration [32].  
SO\({}_{2}\) is added to grape juice/must as an antiseptic, anti-oxidative, and antioxidant agent [33]. A concentration of 50 mg/L SO\({}_{2}\) is typically added during crushing and/or pressing [33]. Cu in juice/must mainly arises from the usage of copper-based sprays in the vineyard (e.g., Bordeaux mixture) and/or excessive Cu uptake from the soil by grapevine [34]. Consequently, a broad range of concentrations of SO\({}_{2}\) and Cu are possible in the grape juice/must before fermentation.  
Given the reactions of SO\({}_{2}\) with volatile aldehyde compounds, and Cu(II) with LMWSCs, there is a potential for increased SO\({}_{2}\) and Cu(II) concentrations in grape juice/must prior to fermentation to trap the aldehydes and LMWSCs generated by yeast. Consequently, Cu(II) and LMWSCs in juice/must may increase the yield of these volatile compounds in the finished wine. Therefore, the aim of this work is to examine the influence of SO\({}_{2}\) or Cu treatments to grape juice/must on the concentrations of aldehyde compounds and LMWSCs throughout the wine production process and after 15 months of bottle aging. The trial was conducted with both Chardonnay and Shiraz grapes with two different SO\({}_{2}\) and Cu levels.