I have tried long-term aged beers (year or more) side by side, one with o2-absorbing crowns, one without, and swear by the difference. While it seems you want some oxidation in a long-term-aged beer, they generally just have a much better flavor/less sherry-like with an o2-absorbing crown.

However, when judging at a competition recently, I had another judge tell me that one should not use these on hoppy beers, as they will absorb the aroma and leave you with a aromaless AIPA/IIPA/APA. Does this make any sense? I would think it would make even more sense to use them on hoppy beers since they oxidize so easily.

  • Unless you have done a blind triangle test to verify that the crowns are actually absorbing O2, I think you might have fallen for the power of suggestion.
    – Denny Conn
    May 15 '14 at 16:59
  • 1
    it was a blind triangle test on both a biere de garde and an oaked braggot.
    – Pietro
    May 15 '14 at 17:32
  • Excellent! Great to hear that!
    – Denny Conn
    May 15 '14 at 18:34

I would be surprised if there is any merit to it, at least as far as my understanding of the science behind the oxygen absorbing crowns go.

O2 can't simply be absorbed - it has to bond with another substance and oxidize it. The idea is that there is a substance in the crown that when activated by becoming wet will bond with O2, causing the chemicals in the crown to oxidize rather than the chemicals in your beer.

Ideally the electrochemical potential favors the oxidation and not the reduction, so the redox reaction proceeds only one way.

If that's not the case and the oxidized scavenging compound is later reduced, releasing the oxygen to later oxidize something else, then perhaps that might later cause more oxidation of the aromatic compounds. But that would be a pretty silly design for a oxygen scavenging cap!


It appears that there are both homebrew and commercial issues with absorbing crown liners causing some issues. There is a tweet circa 2010 by Ray Daniels (Cicerone) claiming 2/3s of a loss of aroma within a couple of weeks.

I don't know how accurate this claim is; however, I can tell you that I use the caps with my beers, and if I'm drinking them within 6 months it doesn't cause much of an issue (even with IPAs). If you're planning on doing some long-term aging, controlling the temp of the beer in the bottle may be more effective at protecting the aromas (storage temp does affect the aromas in a great fashion).

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