The Pasteur effect describes how available oxygen inhibits ethanol fermentation, driving yeast to switch toward aerobic respiration for increased generation of the energy carrier adenosine triphosphate (ATP).
[1] More generally, in the medical literature, the Pasteur effect refers to how the presence of oxygen causes in a decrease in the cellular rate of glycolysis and suppression of lactate accumulation.
[2][3] In 1857, microbiologist Louis Pasteur showed that aeration of yeasted broth causes cell growth to increase while the fermentation rate decreases, based on lowered ethanol production.
While only 2 ATP are produced per glucose, this method is utilized under anaerobic conditions because it oxidizes the electron shuttle NADH into NAD+ for another round of glycolysis and ethanol fermentation.
Second, ethanol has bactericidal activity by causing damage to the cell membrane and protein denaturing, allowing yeast fungus to outcompete environmental bacteria for resources.