Originally Posted by TopherM
I'm not making this up. It's a documented scientific experiment that you can literally watch for yourself. You don't have to take my word for it (like some of the anedoctal evidence others are presenting).
The wyeast video seemed much more like a statement and not a repeated/verified scientific experiment. They don't even mention how full the carboy was. I'm just saying I wouldn't hang my hat on a video with a guy making a statement in blue scrubs.
On another note, I know this thread is old and you've probably brewed plenty of batches since, but there is no harm done in oxygenating after you pitch (except the risk of contamination) if you oxygenate during the lag phase (typically 12-24hrs assuming proper pitch rate). In fact, for really big beers (1.100+) you have to do a second oxygenation prior to fermentation commencing if you want full attenuation.
I won't go into depth on the technicalities but as long as a majority of the cells are in the reproduction phase, the oxygen in the wort is being absorbed (within about an hr) by the yeast to prepare their cell walls for division. Once a majority of the cells have moved into the fermentation phase (24hrs +) the addition of oxygen to wort will not be absorbed by the yeast, instead, it will react with a yeast reproduction by-product that has not yet been cleaned up and result in acetaldehyde (green apple), diacetyl, or fusel alcohols. (Yeast, Chrise White & Jamile Zainasheff)