Wine contains several gases in solution, O2, CO2 and N2, each has an impact on wine style or quality. Oxygen is the dissolved gas that can have the most negative impacts on wine via premature aging, browning and oxidized aromatic and flavour impacts.
That said, oxygen is important at various stages on the winemaking process and an important driver of style for some types of wines (sherry, maderia for example). Before and during ferment, oxygen is important for:
-good yeast health during the exponential growth phase
-for sparkling wine juices to bind phenolics reducing colour and phenolics in base wines
-aiding the volatilization of suphides during fermentation.
While CO2 protects the wine from oxidizing during fermentation. Once primary fermentation is complete, winemakers typically want to protect wines from excess O2 via SO2 additions, prevention of O2 pick up during wine movements and during wine aging. For barrel or oak aged wines, the slow pick up via O2 transfer through oak assists tannin polymerization on red wines and the development of texture and mouthfeel in white wines.
The management of oxygen in wine is critical during the bottling process is the final stage of O2 management where winemakers typically want to bottle with very low DO2 levels to prevent the wine from premature aging via in bottle oxidizing.
DO2 levels should be measured at many stages to ensure limited DO2 pickup, identify low SO2 levels and prevent oxidation using luminescence probes either in wine (in tank, barrel etc) or after bottling to determine O2 pick up using luminescence spot probes.