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I brewed a 1.052 American brown ale and pitched some WY1056 slurry that was 4 weeks old. It was about 24 hours later and not a sign of fermentation so about 3 hours later I gave it a 15 second shot of pure O2 for a second oxygenation. I noticed when I did it, there was a slight krausen starting to form…just barely. So about 1 hour after the O2 shot, it’s going gangbusters and bubbling away. Did I just oxidize my beer because it seems that it was likely to have been going anyway without the O2? Or will the yeast take care of it since it was so early in the fermentation. I’m such an idiot! I should have left it alone.

you will be ok. some people actually add late o2 additions

Later O2 additions help with big beers. As muddy water stated, you will be fine.

Oxidation shouldn’t be a problem because the yeast will have taken it all up in a short amount of time, especially since the beer was on the edge of active fermentation.

You may have caused a lot of diacetyl production by aerating after fermentation had started (however weakly), but the yeast should reduce this by the end of the fermentation.

Chris Colby

I’m guessing oxidation comes from oxygen acting on ethanol and/or fermentation esters, to produce other products we don’t want. If it happened to wort you’d see oxidation in every batch.

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