On one of my trips to the local home brewing supply store an employee of the shop suggested I try something called “Fermcap-S.” It was a little brown vial of liquid, and he told me that it would solve any problems that I was having with boil-overs while brewing. I bought a vial and tried it out with great success, so I looked in to how else it could be used.
What is Fermcap Used For?
Fermcap breaks surface tension, preventing excessive foaming. If you add it to the boil while you are brewing beer it will prevent a boil-over. I have read several stories of brewers boiling seven gallons of wort in a 7.5 gallon kettle successfully with use of Fermcap.
If you add Fermcap to the fermentor after the brew it will prevent excessive blow-off. It is often recommended if you are using a carboy for a fermentor because it prevents the krausen (foam created during fermentation) from filling up the neck of the carboy. I recently fermented a strong porter in an Ale Pail and I still had problems with the krausen exploding through the airlock and causing a mess. I did not use Fermcap on that batch of beer because I ran out of it, but now I wish that I had run down to the home brewing store to pick up another vial.
Another use for Fermcap that did not occur to me, though it may be the most useful application, is for yeast starters. Yeast starter kits come with a pyrex Erlenmeyer flask for boiling/cooling small volumes of wort to use for growing yeast. The problem is that there is a very high risk for boil-overs when using a flask due to the shape and volume of the container. When I create a yeast starter I actually boil wort in a pot and then carefully pour the liquid into the flask after it has been cooled. This is a difficult and annoying extra step. Now I realize that adding a single drop of Fermcap to the flask will prevent a boil-over and make the whole process a LOT easier.
How to Use Fermcap for Brewing
Fermcap comes in a little vial with a dropper attached to the cap. If you are adding Fermcap to the boil kettle you add one to two drops per gallon of liquid being boiled. If you add it to the boil you do not need to add it to the fermentor separately.
If you are only adding Fermcap to the fermentor use two drops per gallon.
If you are using Fermcap in a yeast starter you just need to add one drop, since there is just a small volume of liquid in the flask.
Be careful not to add more than the recommended doses, as this will elevate the levels of silicone in your beer higher than FDA recommendations.
How Does Fermcap Affect the Beer?
If you add the Fermcap during the boil it will not affect your beer at all. It will settle out during the fermentation and it will be left behind when you transfer the beer out of the fermentor. If you add the Fermcap just for the fermentation it will increase the retained bitterness of the beer by about ten percent.