I use plastic PET carboys ("Better Bottle" brand) for fermentation, mainly because they're cheaper, lighter, and safer. I use only chemicals to clean them (no brushes), so I'm not too worried about scratching.

However, I'm getting ready for my first lager and wonder if I should get a glass carboy, since the beer will be sitting in it for much longer and I don't want too much oxygen getting in. I've heard that PET bottles have pretty low oxygen permeability (compared to a plastic bucket, say), but it's probably higher than glass.

So is it worth it to get a glass carboy? Or is my airlock / stopper going to let in way more oxygen comparatively, and it doesn't really matter what the carboy is made of?

2 Answers 2


I use the better bottle PET carboys for my lagers, and have noticed no oxidization. The amount of oxygen introduced through the carboy itself is negligible compared to the amount introduced through the stopper or when racking to the bottling bucket or transferring to keg.

The Better Bottle page discussing permeability aims to show that plastic is fine for long term ferments, and the linked report shows that brewers regularly deal with oxygen levels far greater than those due to permeabilty of PET, which is why the permiabilty can be considered negligible compared to other sources of O2.

  • 1
    Well, there ya go!
    – Denny Conn
    Jun 2, 2012 at 21:03
  • Or in a pinch, get an 'even better bottle' at the grocery store that includes some clean tasting Primo Water to brew with, hehe.
    – Dale
    Jun 3, 2012 at 13:03

AFAIK, the Better Bottles are pretty impermeable so I think you should be OK. The sensible thing to do would be to contact the company that makes them and ask about long term storage and permeability.

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