Originally Posted by Gear101
How does oxygen get into a sealed fermenter because someone shook it, if it was that way then infection would be ramped without shaking it. The presser inside the ferm is higher than the outside, so air would not be able to get to the beer. Now with that said, this isnt something I do on normal bases, but have had to do it to unstick a beer, to get the yeast off the bottom like a stir plate and a starter. Cheers
Correct. While shaking it isn't advised, a gentle swirl is okay to rouse some yeast. I have to do this when I brew a porter with London ESB yeast. It flocs to quick and hard, I rouse it to finish the job and do a D rest.
When fermentation starts, pretty much ALL the O2 is pushed out, as it's lighter than Co2. Swirling it introduces little to no O2 as it's been all pushed out once active fermentation takes place. There could be a little residual in there, but more than likely not enough to matter.
A full on shake isn't advised though, but a little swirling action to get the cake moving is fine.