Torulaspora delbrueckii metabolism was assessed in a synthetic culture medium similar to grape must under various conditions: no aeration and three different oxygen feeds, in order to determine the effect of oxygen on metabolism. Carbon and nitogen mass balances were calculated to quantify metabolic fluxes. The effect of oxygen was to decrease the flux of carbon going into the fermentation pathway in favor of growth. In the absence of aeration, higher amounts of glycerol were produced, probably to maintain the redox balance. The oxygen requirement of this starin was high, since even for highest air supply oxygen became limiting after 24h. Nevertheless, this strain developped well in the absence of oxygen and consumed 220g/L of sugars (glucose/fructose) in 166h at 20°C, giving a good ethanol yield (0.50g/g).