I was talking with a fellow brewer who has been brewing for many years and found out that he does not put any liquid in his 3 piece airlocks. He claims that next to nothing can get in even without the water that there so he just stopped, and he claims the water is just to see the gas coming to to show that it is fermenting.

Is liquid actually required in the 3 piece airlocks?

note: his beers always taste great and never seem to get infected.

  • 1
    How long does he let them sit that way? My concern would be oxidation...
    – baka
    Sep 10, 2012 at 20:30
  • However long he leaves them in his fermenter. Sep 10, 2012 at 20:35
  • What's not needed during active fermentation is the "bug cap" (the plastic cap with the tiny holes). If you happen to get krausen into your airlock and you have the bug cap on, that is when you may need to use the mop on the ceiling! Without the bug cap, that fate is less likely. Of course a blow off is recommended, but it's not quite as easy, and so not always done.
    – Dale
    Nov 11, 2012 at 15:45
  • 1
    But a bubbling fermenter airlock is one of the loveliest sounds on earth! Mar 3, 2016 at 0:18

2 Answers 2


Look up Pasteur's goose-neck flask experiment.

Passive environmental dust/contaminants wouldn't be able to get through a 3-piece airlock, no.

More active actors (fruit-flies, spiders, ants, &c.) would; liquid would be an effective deterrent to them.

As mentioned, gas exchange would be possible w/o liquid. During active fermentation, there's enough pressure from the produced CO₂ to prevent this very effectively, but once fermentation subsides, the air will begin to mix/normalize with the CO₂ in the headspace. The relatively small area of the airlock stem would limit this pretty effectively, though, I would think.

  • I agree I would have said the same thing about the gooseneck. But one thing I wonder about, the gooseneck is long, maybe that helps it peform well compared to a short stubby airlock.
    – mdma
    Sep 10, 2012 at 22:11

Liquid in the airlock is required if you want an airtight seal.

If you don't care about having an airtight seal, then you don't need liquid. By not having an airtight seal, you risk air getting into your fermentor and bring along things which you may not like (i.e. oxygen, bacteria, etc.). Now with the 3 piece, the risk is less because you at least have a piece of plastic resting on the tube which actually enters the carboy. But, alas, it is not an airtight seal.

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