Yep, that's right, you can ferment in a keg.  Think about it.  Of all of the pieces of equipment that we have that look like something you would see in a brewery, the keg most resembles a cylindro-conical fermenter.  Stainless is easily cleaned and your keg's shape is suited for fermentation.  And once you are done with fermentation, it is so easy to "siphon" / pump your beer out into a serving keg.  Or hell, just serve with a bit of sediment right out of that keg.  The first few pints will be a bit "rich" but overall, still not bad.

So, what do you need to know about fermenting in a keg?  We'll break the two high tips into two weeks.  Overall, kegs work best as secondary fermenters.  You don't want too high of a fermentation going on in your keg as it will have a really fun time with creating a mess on the top of your keg.  But in a secondary fermentation role after you have siphoned out of your primary, the keg will do great to help wrap up the fermentation and let your yeast and sediments fall to the bottom.

One big concern obviously is trying to find the best way to vent carbon dioxide as it is produced.  You could just open the valve on top of the keg, but nobody really likes having their beer open to the environment.  Sure, there should be positive pressure coming out, but you can't be really sure that you have that all of the time, a mischievous bug could try to work its way in there, and you really can't track the secondary fermentation.

The solution is actually backwards.  What you want to do is attach one of the fitting you use to put carbon dioxide into the keg and have that attached to a short piece of tubing that you can have go into a small jar of water or sanitizer.  You use the "in" as an "out."  It is kind of a no-brainer.  The CO2 comes out of the air fitting which is at the top of the keg and bubbles straight into your jar, creating a simple airlock.  Obviously, you want to watch for that somehow getting full of gunk, but at the same time, you really don't have to worry too much about an exploding carboy anymore because your keg can take 100+ psi. 

In our next tip, we'll give you an idea for converting your keg into an even better fermenter.