What can oxygen do to fermentation?

[PatMac]

Long story short - I peaked in my fermenter last night to see if there was any activity going on after 48 hours. When I got home from work tonight I realized that the lid hadn't snapped all the way shut after I closed it.

The krausen is forming, and I don't think that anything got inside the bucket as it was barely open and I assume the gas simply found its way out through that instead of the airlock.

My question from this is what can oxygen exposure do to fermenting wort? Does it just increase the chance of infection because more bacteria can live in it? Or is there an off flavor change that can occur?

 

[Edcculus]

During active fermentation you have 2 things going for you

1- formation of CO2 will drive off the oxygen
2-the thick krausen cap will keep oxygen from actually getting to the beer.

A lot of older breweries ( and some new) employ open fermentation with some yeast. I know Sierra Nevada does it with their Kellerwiess. A lot of Ringwood breweries also open ferment. No worries dude!

 

[ChshreCat]

+1 CO2 was pooled on top of your beer so it's unlikely very much O2 ever came in contact with it. The line on my main fermenter doesn't even seal enough for my airlock to work. I haven't had oxidized or infected beer yet.

 

[mc_eric]

My question from this is what can oxygen exposure do to fermenting wort? Does it just increase the chance of infection because more bacteria can live in it? Or is there an off flavor change that can occur?

That's an interesting question actually, I wonder what oxygen would to a beer if was added during active fermentation (you probably didn't get any oxygen in your beer, co2 from the fermentation would have kept it out). I've heard of clones of Dogfish Head 120 min where they add oxygen every day for the first week or something like that. In that case, They're trying to get it up to 20% abv with absurd amounts of sugar. I wonder what that would do to a normal strength beer though? I bet it would have the same affect as oxidizing the beer after fermentation, as the yeast probably wouldn't use it up, and just cause the beer to go stale over time (I think the yeast really only uses oxygen during the reproductive phase right after pitching).