Some brewers like to use Corny kegs as fermentors. Although some published articles have commented on the less-than-optimal shape of the keg for fermenting (too tall and narrow), it is an option that has worked well for many.

Primary fermentation: About the easiest way to temporarily set up a keg as a primary fermentation vessel is to simply remove the entire gas IN valve assembly and tube. Slip a length of 1/2-in. i.d. vinyl tubing over the threaded fitting and run it into an airlock.

If you brew beers that typically have enormous amounts of blow-off, you can modify a keg lid for dedicated use as a fermentor by drilling a hole big enough for a blow-off hose. Enlarge it if needed using a hand grinder or a file. Fittings, washers, and seals available at your local hardware store will enable you to use a blow-off tube that's larger than 1/2 in.

Secondary fermentation: To avoid these modifications and the cleanup associated with primary fermentation in Corny kegs, you can use them only for secondary fermentation. After completing the primary in an open fermentor, I rack to an unmodified, sanitized Corny. Every other day or so I relieve gas pressure that builds up inside the keg by simply pressing the gas-side valve or the pressure relief valve open for a second or two.

Fermenting under pressure. For those who want to ferment under pressure to naturally carbonate their beer, constant-pressure relief valves can be purchased for both ball-lock and pin-lock kegs. Lager brewers in particular will find it useful to control and maintain the pressure in the keg as the temperature drops slowly and the pressure increases. Typical adjustable relief valves are spring-loaded and can be set to relieve pressures between 5 and 30 psi. They attach to the keg's quick-disconnect fitting.

After the secondary fermentation is complete (or if I'm lagering), I prefer to rack a third time to a sanitized Corny keg. This final keg is placed in the fridge for force carbonation, cold conditioning, and draft dispense. Every time the beer is racked from one container to another, however, the chance of aeration and infection increases, and you may be uncomfortable using this technique. With careful handling, however, you won't experience any problems.

An alternative is to leave the beer in the primary a little longer than normal before racking it to the secondary. The longer settling time will generally result in less sediment by the end of secondary fermentation. The secondary fermentor then also serves as the dispense tank, with the addition of a modified dip tube (the tube that's in the OUT side of the keg).

A popular recommendation for this application is to cut off the bottom 3/4-1 in. of the long dip tube using a tubing cutter or a hack saw. After filing the end to remove burrs, reinstall the tube in the keg. The shortened tube will prevent the pickup of sediment during dispensing of moderately to strongly flocculant yeast strains.

Another approach that works well is simply to add gelatin or isinglass finings to the beer on final racking from the secondary to the final tank and before cold storage. When well mixed, the finings will drop any remaining yeast to the bottom of the keg, and even unmodified dip tubes won't pick up the sediment.