micro-oxygenation in contemporary winemaking - Cape Wine ...

Micro-oxygenation in Contemporary Winemakingwine depends on the rate of oxygen addition. Rapid exposure to high doses of oxygenquickly overwhelms the wine’s capacity resulting in oxidation and browning. However, thesame wine could tolerate fairly large amounts of oxygen administered in small dosesbecause the oxygen is slowly consumed through reactions with phenols. It is these slowoxygen-induced polymerisation reactions that are implicated in the positive changesassociated with wine ageing (Fulcrand et al., 2006; Ribéreau-Gayon et al., 2006a), and it isthese types of reactions that micro-oxygenation seeks to emulate (Lemaire et al., 2002;Bautista-Ortín et al., 2007).In addition to phenolic composition, a wine’s ability to consume oxygen will also beinfluenced by other factors such as the availability of alternative substrates, anti-oxidantsand oxidation catalysts. The principal anti-oxidants in wine include SO 2 and ascorbic acidwhile metal ions in wine act as important catalysts of oxidation reactions (du Toit et al.,2006b; Danilewicz, 2007; de Basquiat, 2008). Yeast lees have a very high oxygenabsorptive capacity so the presence of lees will also significantly increase a wine’s ability toconsume oxygen (Fornairon-Bonnefond et al., 2003; Salmon, 2006; Mazauric and Salmon,2006).If the rate of oxygen addition is lower than the rate of oxygen consumption in phenolicreactions then oxygen will not accumulate in the wine. So the optimal oxygen dose inmicro-oxygenation should not produce an increase in the concentration of dissolvedoxygen (Paul, 2002). This principle is used in the monitoring of micro-oxygenation (Pour-Nikfardjam and Dykes, 2003) but it should also be noted that the dissolved oxygenconcentration depends on the solubility of oxygen in wine which is very temperaturedependent – wine at 25°C and completely saturated with oxygen would contain 7 mg O 2 /Lwhereas at 5°C the figure would increase to 10 mg/L.5.2 APPLICATIONS OF MICRO-OXYGENATIONMicro-oxygenation is not appropriate for all wines (Parish et al., 2000). Micro-oxygenationis simply another technique available to winemakers and if used at all, its use must betailored to specific circumstances and particular wines.Following the potential benefits of micro-oxygenation listed in Section 4.1, some of thepotential applications of micro-oxygenation and the key choices that need to be made aresummarised in Table 3. The vast majority of micro-oxygenation applications have been in16