At what stage is Oxygen bad?

[justin22]

I was under the impression that Oxygen was bad for the Fermenting beer. Yet, when I had a weak fermentation some one told me to check the SG by opening up the fermenter. Anways swim wants to see if his krausen has settled and if he can move it to a secondary. Also he wants to check the SG. Would this not be recommended.

 

[bob1852]

just opening your fermenter to grab a quick sample or to rack to a secondary won't be a bad thing.

Just don't open it up and put in a 125HP boat engine and open the throttle.

 

[GreenwoodRover]

Don't listen to him:
125HP is ok, I draw the line at 175HP

 

[ifishsum]

Before fermentation, oxygen is beneficial. Once it's started (and especially once it's finished) it can cause oxidation in the final product. It takes a while to form though (months) so it's only a big issue if the beer will be stored for a period.

Simply opening the fermenter will likely not expose the beer to oxygen, because there is a layer of CO2 (which is heavier than air) protecting the surface. Even without that, surface oxygen transfer would be minimal. You'd have to stir and splash it to cause a significant problem IMO.

 

[WorryWort]

+1 on the above. if the yeast is still active even moderate amounts of O2 can be eaten up and reabsorped by them.

I only ever had one problem, and it was from an old beer. Just take care when racking that you don't splash and bubble the beer. That's probably the easiest way to introduce oxygen and it's a bad time to do it too!

 

[blowmax10]

should I start the "hot side aeration" debate again?