Oxygen "Absorbing" Caps
 

I was looking at the Sierra Nevada site not too long ago, and they began talking about a type of beer cap that provided an oxygen barrier. They said that the plastic liner in this cap was harder than the standard bottle cap, and thus prevented oxygen from getting it (but, of course, didn't "absorb" the oxygen that was in the headspace).

So this got me thinking. I'm not 100% on this -- and anyone feel free to correct me if I'm wrong -- but I believe oxygen "absorbing" caps don't actually absorb oxygen, but do a better job of preventing it from leaking in. The plastic lining of the cap is harder and more impervious to oxygen transfer. Kinda like a bucket (standard cap) vs. a better bottle (oxygen absorbing cap). Indeed, Austin Homebrew advertises their caps as "oxygen barrier," not "oxygen absorbing." They appear to be the same silver cap advertised everywhere else as "oxygen absorbing."

Any thoughts?

I have wondered about this also. I heard that they are activated when they get wet, but that doesn't make sense, because they have to get wet to be sanitized. So unless you sanitize each cap individually immediatley before placing on the bottle, oxygen absorbing would have already happened probably.

AHS says they help in long term storage, so I think oxygen barrier makes more sense than oxygen absorbing. They barely cost more so I use them, but don't really know how they work.

There is a compound under the gas permeable liner that does absorb oxygen. Its activated when it gets wet. Therefore you can not boil or soak these caps before using. Some home brewers, myself included do not sanitize the caps before putting them on the bottle. Several of the major beer makers, Coors for one, do not sanitize the caps either.

They really do absorb the oxygen in the neck. its not just a barrier to prevent O2 from getting in.

I'm definately not putting anything on top of my beer that has been sitting out without it being sanitized first. Even though they're in a bag in a cabinet, they sit around for months, and I open up and stick my hands in that bag every few weeks. No way am I not sanitizing those caps.

I didn't sanitize them when putting them on, so I suppose that's a good thing (although I did rub the lip of the bottles with a star-san rag whenever I over-filled and spilled a bit). I read a lot regarding the pros and cons of sanitizing caps, and figured with the beer having an alcohol content, and also the fact that I don't plan to shake the brew up (making it come in direct contact with the cap), I'd be fine. Oxygen is required by most (but not all) nasties that would thrive in a 5%+ ABV solution, so I suppose win-win.

I was a pretty big nit about sanitizing every thing else, the bottles included, so I'm going to hope for okay-ville. If I get some funky bottles out of this batch, I can pretty much conclude it was the lack of cap-sanitation.

You are doing yourself and your beer a disservice. No brewery sanitizes their caps. The alcohol in the beer will kill any contaminates. You need to cap and then invert for the oxy caps to work. If you sanitize them you lose the oxygen absobing properties.

Oxygen barrier and Oxygen absorbing caps are the same. Everyone sells the same caps from the same distributors.

Forrest

Well Forrest, you have caused me to question my practice of sanitizing my caps. It just seems really funky not to do it. Maybe it's the "old habits die hard" syndrome.

So I should turn the beers upside-down to activate the cap? Won't the gradual buildup of humidity in the bottle take care of that, or is inversion necessary?

I think the idea is to purge the O2 in the neck as quickly as possible to eliminate any potential effects on the beer. Therefore you wouldn't want to wait days or weeks in hopes that enough moisture accumulated to activate the caps.

If Forrest says to invert the bottles, turn them over. If it's too inconvenient, Use regular caps. I've had great luck with bulk normal caps lasting for years....just don't jostle your bottles about!