Lately I've been doing some very large boils -- 7 gallons in a 7.5 gallon kettle. To prevent boilovers, I've been using Fermcap-s. It's great, and I've had no boilover problems, but I have no idea how Fermcap works or what's in it. What is this stuff? Other than preventing boilover and excessive kreusen, does it have any effect on my beer?


4 Answers 4


Fermcap-S is a silicone (Dimethylpolysiloxane) based emulsion that works by breaking surface tension. It has no effect on the finished product if used in the boil at designated dosage. If used in the fermenter, I have read that it will increase residual bitterness by ~10%. This is likely due to the compound binding to the yeast cells before the dissolved bittering compounds do, thereby leaving more bitterness in the beer. I have not verified this myself.

Stick to recommended dosage, or you will exceed FDA guidelines for silicone content in your beer.

This thread at BeerAdvocate covers the topic: Fermcap-S (login required)


The FDA has recently decided that Fermcap S should be filtered before you drink your beer. Fortunately, there's Fermcap AT which is fine to use without filtering.

Here's some info from Birko, which makes a product very much like Fermcap..

"Brewers should not use silicone-containing antifoam for unfiltered beers. The FDA allows active silicone to be used up to 10 parts-per-million (ppm) but stipulates that the silicone must be removed prior to packaging by either filtration or centrifugation. In the case of unfiltered beers, use a food grade, non-silicone antifoam. We sell a food grade, canola oil based antifoam that works well for this purpose and has an added benefit of being yeast-friendly at the same time. Look for my article on antifoams in the brewery in the July/August issue of The New Brewer. Please contact me directly if you would like to discuss this or any other matter further.


Dana Johnson Brewery Technical Representative BIRKO Corporation Henderson, Colorado www.birkocorp.com:

  • Could you link to something that describes this decision?
    – Hopwise
    Commented Apr 12, 2011 at 19:05
  • I'll try to find it, but it may take a while. IIRC, it was on the probrewer forum.
    – Denny Conn
    Commented Apr 12, 2011 at 20:53
  • Here's info from a guy at Birko, which makes a product very much like Fermcap...
    – Denny Conn
    Commented Apr 13, 2011 at 15:10
  • So a guy that's selling a competitor to fermcap says don't use fermcap. This is not the most convincing argument. Still, I'll probably give Fermcap-AT a try if I can find some.
    – Hopwise
    Commented Apr 13, 2011 at 17:36
  • 2
    Here is the regulation that limits occurrence of the active ingredient in Fermcap to 10 ppm. Commented Oct 15, 2014 at 18:49

If a drop of this product were, liberally speaking, 1 mL, then 1 mL / 18.9 L (or 5 gal) = 1/18,900 = 5.291 x 10^-5. And (5.291 x 10^-5) x 1,000,000 is equal to 52.9 ppm. This is above the allowable level stated by FDA. However, if a drop of this stuff is actually much less (eg, water is approx 50 to 70 µL per drop) than 1 mL, say 0.10 mL, then 52.9 ppm/10 would be almost two times below the allowable level at 5.3 ppm. I think it would be safe without filtering before packaging the beer.

  • See Denny's answer above, which states that the silicone (up to 10ppm) should be filtered, it doesn't say that under 10ppm is ok and can be left in the beer. However, the information quoted seems to have appeared from nowhere and searching for the first sentence shows it's frequently quoted and without attribution to source - so credibility is not certain.
    – mdma
    Commented Aug 8, 2013 at 11:54

Don’t use fermcap in your kettle . You are better of playing with your temp setting for your boil . You want a slow roiling boil in your kettle . I have been a brewer for over 25 years at a large brewery . Gaining control of your temp setting in your kettle will improve your beer quality over the long term and more consistent flavor

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.