[skyler]

An efficiency jump and the world's worst stuck sparge made me rethink my brewing plan and I ended up with 6 gallons of 1.12 wort. It's zero-adjunct, and was mashed for dryness (45 mins at 142F - 30 mins at 160F). The resting temperatures and super high gravity are both due to this being my first attempt at decocting. The yeast strain I am using is Imperial Gnome (similar to Wyeast 3522 Belgian Ardennes). The wort was mostly Best Pils with some Best Dark Munich and a pinch of CaraRed.

I added pure O2 before pitching an appropriate amount of dense slurry, but I want to know when and if I should re-oxygenate the actively fermenting beer. Activity was visible about 6 hours after pitching, and it's pumping along steadily now at 66F (30 hours after pitching). So when do you add extra O2 to your beer?

[RC]

I wouldn't add more O2 at this point. If fermentation is well underway, adding more O2 will likely do more harm than good. If you're going to add a second dose of O2 to a high-gravity wort, you want to do so before the growth phase begins, before alcohol gets produced. Otherwise you may end up with an acetaldehyde bomb.

[hopfenundmalz]

If I give a second dose it is 12-18 hours in. Too long for you now. The quick start says you have a good pitch of viable yeast. I think you are good to go.