I agree with ocluke. I believe Palmer states in one of his writings that the yeast only use up around 30% of the oxygen in the headspace. The rest of oxygen has significant impact on hop aroma and flavor. Hop aroma compounds are very susceptible to oxidation- if you have ever had a growler...
Correct me if I'm wrong, but from what I know from my Cell Bio classes is that yeast are facultative aerobes (meaning they use Oxygen when they can, but in the lack of oxygen will switch to fermentation) will undergo an exponential growth period due to a surplus of nutrients (in our case malt...
