For my last 1 gallon batch, I decided to avoid my common problem of overflowing my airlock, by using a proper blow-off. So I bought myself a stopper, hose, and double-sided barb from my LHBS. I gently plugged the carboy, but the stopper started pushing out. So I tried again; same result. So, I pushed it in a little further and harder. Great, it stayed in place! Fast forward 2 days, and super-active fermentation has stopped, so it's time to replace it with a proper 3-piece airlock.

And now I can't get the stopper out. I will figure out how to get it out (while somehow not contaminating my beer, I hope)... but just how far am I supposed to insert a stopper, keeping it airtight and removable?

  • 1
    You could run a tape seal around the lip of the stopper and bottle to keep it in place during active fermentation
    – uSlackr
    Commented Jul 17, 2013 at 13:41
  • I was having the same issue with the bung, so I ordered some of these Carboy Caps. I think they will work much better. homebrewsupply.com/universal-cap-carboy-cap.html
    – user13904
    Commented Jul 14, 2016 at 18:14

4 Answers 4


Can't say there is much of a scientific answer to this question. If I had to guess though, I'd say I definitely wouldn't want the bung flush with the top of the carboy, maybe at least 1/4 - 1/2 an inch protruding from the top of the carboy. That way if it does get stuck, I could use something to grip onto it and pull it out. Typically it's safe to just go until it's snug, and you should be good. I've never had a bad seal from just pressing until it's snug. If the top of the bung is flush with your carboy (without applying unreasonable "hulk-smash" force on pushing the bung in), it is too small, because at that point, it could theoretically fall in with enough force. Mine never run that risk, so you may want to consider going one size bigger.

In the meantime, I'd imagine a wire coat-hanger bent to form an "L" shape would be able to fit through the hole in the bung pop it out fairly easily, so long as it isn't wedged in way too tight.

EDIT: I misread part of your question. When you say you try to push in the stopper and it pushes back out, by how much? It may still have a sufficient seal. Depending on the material, you may also try spraying the stopper with starsan before pushing it in, and the liquid may (or may not) cause it to seal without pushing out. I retract my previous suggestion of going bigger, as it sounds like if anything, your stopper may be too big, judging by how much it is pushing out. My guess is though that your seal is just fine, and the cork is the appropriate size.


2 words...duct tape. I frequently use it to hold stoppers in place. BTW, I have found that StarSan exacerbates the problem. It makes things slipperier.

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    I also find that Star San makes it hard to get stoppers to stay in place. Commented Jul 17, 2013 at 18:33

I have found the drying the lip of the carboy and stopper to solve the problem... If you are using a rinse-less sanitizer the drying is more often than not the part that causes the sanitary condition so keep that in mind.

  • I've tried drying many times and it doesn't work for me unless I also duct tape the stopper in. Seems like it should, and it obviously does for you, but not here.
    – Denny Conn
    Commented Jul 19, 2013 at 18:22
  • I know it may seem obvious for me but did you dry both the bung itself and the lip and inside of the carboy as well?
    – O'Mutt
    Commented Jul 22, 2013 at 17:37
  • Yep. I dry them all every time with a paper towel, which is sanitary right off the roll. Once in a while it will work, but I always tape the stopper in just in case.
    – Denny Conn
    Commented Jul 22, 2013 at 18:19

Finally got a chance to do another brew yesterday, and try the stopper again. This time, I inserted it only once, and it stuck. Since then, it seems to have pushed out juuuuust a little, but it seems good. The blowoff is bubbling like a perfect heartbeat.


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