Rookie mistake: oxidation while fermenting?

First of all, you shouldn't ever seal the carboy. Buy an airlock that fits your carboy.

Hopefully it is fine, but you're biggest concern should be infection. Oxidation risk was probably minimal because active fermentation will produce a lot of CO2 to push out any oxygen right now. Bacteria and wild yeast may have gotten in your fermenter, if you notice a pellicle form (it looks like a fuzzy bubbly fungus) on the top of your beer you have an infection. If that happens you might get a sour dunkelweizen.

Next time this happens, don't seal the carboy or, as you observed, the pressure will bust through your seal. You can cover the opening of your carboy loosely with a crimped piece of sanitized foil if you don't have an airlock. Don't cover it tightly otherwise pressure will build and blow it off. CO2 will still be able to escape but bacteria won't come in due to their inability to turn tight corners (weird, but true).

Also, since you mentioned the yeast went through the opening, you may want to get blowoff tube setup. If your airlock gets clogged during a vigorous fermentation, it will build pressure and explode a terrible mess onto your ceiling. A blowoff tube will lessen that risk.

 

Oxidation is not a concern as long as the beer is fermenting.

The risk of infection is dependent on your brewing environment. I have read where some homebrewers conduct open fermentations. The aspect that I would personally be most concerned about is flying insects like fruit flies. Fruit flies are covered in bacteria and if they get into the beer the bacteria could result in off-flavors in the beer (i.e., an infection).

Since you are now sealed up you are now protected. It is possible (likely?) that nothing got into your beer that will create an issue. Just let the fermentation 'ride' and think happy thoughts.

In the immortal words of Charlie Papazian: RDWHAHB (Relx, Don't Worry, Have a Homebrew)!!

Cheers!

 

I'd say it's not much of a concern while the fermentation is roaring along, but more of a concern once it starts to wind down. In OP's case, it may well have still been ripping along, given the timeline he described.

 

RDWHAHB

 

I would be as concerned about the temp. If the ambient temp is 75 that means the wort could be as warm as 80.

 

Yeah, that's a little toasty. OP is making a Dunkelweizen, so it's possible he's using a hefe strain that won't go as far off the rails as most other strains at high-ish temps. But I'm not sure, as I've never pushed a hefe strain that high.

 

Welcome to the BA site and to the Homebrewing forum, ChickenBear. Those are all good answers above to your question, so I won't add to them. However, to make your brewing session a more complete learning experience, I'll mention that your beer is fermenting at a temp that is too warm for being ideal, and the extra warmth likely was a partial cause for the intensity of the fermentation.