I set up my Blow tube as I have done other times before, (the same as pictured in this post What is a proper blow-off tube setup?)

This time though when I checked it after after about 24 hours the yeast was going to town giving me a bubble about every second and it had siphoned about a gallon of my wort from the carboy into the bucket.

Any idea as to what would cause this result?

  • I wouldn't really describe it as a siphon. It's just krausen being pushed into the blowoff from a highly top-cropping yeast. Maybe the title should be changed to something more arbitrary, like 'Beer Lost through Blow Off Tube"?
    – Brandon
    Dec 22, 2010 at 4:12
  • 1
    Instead of using a blow off tube you can use anti-foam agents like fermcap-s to limit the foam in the primary fermenter. You add it when the foam is a few inches below the neck of the carboy. Whatever is added drops out after fermentation and doesn't affect the flavor and aroma and saves some of your beer from blowoff. northernbrewer.com/brewing/brewing-ingredients/salts-finings/… Dec 23, 2010 at 15:24
  • What size is your carboy? How full is it? Dec 23, 2010 at 22:39
  • Whatever your solution, Northern Brewer Chris makes a good point in recommending Fermcap-S. The stuff is amazing. Also great for preventing boil-overs during the boil.
    – markskar
    Jan 3, 2011 at 17:22

2 Answers 2


Very active yeast and/or an overfull fermentor. You could also have the tube jammed too far into the fermentor. It just needs to be in far enough to not get forced out from the pressure.

Some yeast just habitualy blow-off a lot, too. I had 2.5 gallons of starter wort and Wyeast 3787 in a 5 gallon carboy that blew off a little bit. Everyone I know has issues with that particular strain blowing off, too.

It's a fairly regular occurence for me, and it will still make great beer. Just make sure you're blowing off into something with enough volume to contain the mess.


You should be using a 6+ gallon carboy for a 5 gallon batch of beer for this reason. There needs to be enough room for the thing to kreusen up without blowing everything out.

  • It was a 5.5 gallon carboy (supposed to be used as a secondary) and had 5 gallons in it. Fermentation has pretty much stopped and it looks like about 1 - 1.5 gallons left the carboy. Dec 27, 2010 at 15:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.