I'm wondering what other peoples' experiences are with krausen at the start of fermentation. I've had some beers that have bubbled along happily without producing huge amounts of foam, and others that seem like they'll neve stop spuming. This weekend we started a stout and I installed a small plastic airlock. By 7 AM the next morning there was krausen up through the airlock, down the sides of the carboy, and trickling away in a tiny stream. I cleaned everything up and switched to a larger diameter hose with its end in a bucket of water so the foam had somewhere to go, but there seems to be substantial quantities of wort being lost by this (I'd estimate 1/3 gallon in this case). Are there things I can do to control this? Are there ingredients, or styles of beer, or strains of yeast that tend more towards producing big, frothy krausen? How are other people dealing with this?

  • Ran into this very issue over the weekend. Thank you for asking.
    – mummey
    Nov 24, 2010 at 9:24

3 Answers 3


A healthy fermentation with a strong yeast will tend to produce a larger krausen. You're right about the strain of yeast being a big player, but the best thing you can do is increase your fermentor head space.

In this case, the obvious answer is best: either use a larger carboy or smaller volume of wort. You can also get a little help by fermenting cooler to slow yeast metabolism, but this will affect the flavor profile.

Additionally, there are silicon defoamers like Fermcap and Foamtrol that will help - if you don't mind breaking the Reinheitsgebot. Personally, I don't like chemical additives, but they're FDA-approved and many homebrewers swear by them.

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    I'm much more concerned with minimizing waste and the need to clean than adherence to old-tyme beer laws. Thanks for the tips, I'll look into the defoamers. Nov 22, 2010 at 19:21
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    It's not so much about adhering to a law that was written before the discovery of yeast as it is that some people prefer not to add artificial compounds to their beer. FWIW, I've tasted the same recipe brewed with and without Fermcap, and it didn't seem to suffer from the additives.
    – Brandon
    Nov 23, 2010 at 5:08
  • Thanks, I used a 6.5 gal. carboy for an IPA I've got brewing currently (as opposed to the 5 gallon I'd use before) and it's had sufficient head space to deal with the krausen. Jan 4, 2011 at 4:58

I'd suggest using a pail for a primary instead of a carboy. There seems to be a bit of a Canada/US cultural difference here. I think most Canadian homebrewers would consider the term "primary fermenter" to refer to a large food-grade bucket. The ones we commonly use here are about 40 litres, giving plenty of head-space for a 23-litre batch.

  • Unfortunately I've got one plastic pail fermenter and 5 carboys of various sizes which I've acquired over the years. I suppose I could get more buckets and use the glass fermenters for secondary. Nov 22, 2010 at 19:22
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    That sounds like a perfect ratio to me ... make a batch, put it in the plastic primary for about 2 days, then into one of the waiting empty carboys.
    – Jeff Roe
    Nov 22, 2010 at 19:54

There is a product out there called Fermcap-S. You drop a drop or two into the boil or primary and it prevents foam buildup. The ingredients are insoluble and don't seem to affect the flavor or head-retention of the finished product. The ingredients settle out during fermentation. From my experience it works great. I don't even have to watch the boil for boil-overs.

It comes in a small eyedropper bottle and you can probably find it at your LHBS.

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