Fermenting In A Keg

Many homebrewers like fermenting in a keg. With the price of glass carboys going up, not to mention the danger involved in transporting the heavy glass containers around from place to place, it makes sense to buy another corny keg instead.

There are many advantages but also some problems. One problem is that many fermentations produce a lot of krausen (or foam) which will plug the small openings in the keg. The only solution I know of is to use Fermcap-S, a product that reduces the krausen to about 1/2" and prevents the need for some type of blow-off tube.

I have heard of several ways of fitting an airlock on the keg. One is to find an extra lid and drill a hole big enough to use a rubber stopper with an airlock. You can remove the poppet from the gas "IN" plug, heat the end of a small length of 1/2" OD tubing and fit it over the plug. The airlock fits in the other end. I have also seen where the pressure relief valve is removed and a piece of 1/2" tubing is forced in the hole, with the airlock on the other end. Midwest Supplies sells a Keg Fermentation Kit (#9305) which has a special gas-in plug fitted with a 90° ell of stainless tubing. A piece of 1/2" tubing fits over the end of the stainless tubing with an airlock on the other. They also use the Fermcap-S to prevent blow-off while fermenting in a keg. Regardless of how you attach an airlock, you won't be able to ferment a full 5 gallons of wort in the primary. There will always be some amount of krausen formed and this necessitates having a little head space in the keg.

To transfer from the keg to another keg for secondary, you will have to rack under pressure. To do this, you must shorten the long "beer out" tube in the primary keg from 1/2" to 1" using a tubing cutter or hacksaw (be sure to file off the burrs). By shortening the dip tube you will leave the trub and yeast in the bottom of the keg. The keg used for secondary shouldn't need an airlock since it won't generate much pressure while clearing, but you can swap out the airlock fittings if you wish. Otherwise you will need to "burp" the keg by releasing CO2 pressure with the pressure relief valve periodically.

One advantage of fermenting in a keg is that you can cut out almost any chance of oxygen reaching the beer. You can purge the kegs prior to racking by either leaving the lid unsealed and filling with CO2 for a 20-30 seconds prior to racking or by filling the keg with sanitizer and pushing all the sanitizer out with CO2. If you decide not to purge the entire keg, make sure you purge the head space after filling with beer. Using your racking cane or auto siphon is the same for a keg or a carboy. Try to keep the end of the hose on the bottom of the receiving keg and below the surface of the beer at all times to prevent splashing and aerating the beer or wort.

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