This article will attempt to describe using a keg as a fermenting device. The method is very simple. Initially, you will either need to cut around an inch or so off the bottom of your liquid-out dip tube OR (ideally) install a top floating dip tube. I prefer the floating dip tube method because it serves clearer beer quicker off the top of the keg and doesn't irreversibly alter your gear.
As far as a blow-off tube you can use a simple hose attached to the gas ball lock as shown above in the image, or install a spunding valve. I generally wait to install the spunding valve until day 2 or 3 just to make sure it doesn't get clogged up with krausen.
For volume, you will need to reduce the batch size around 0.5g. For example, when I use a 3g keg, I generally brew a 2.5g batch. However, I sometimes use FermCap S (just a few drops) prior to yeast pitch. It's an anti-foaming agent that settles out after cold crashing and does not affect the taste of your beer. It helps to reduce the krausen layer so you can fill the keg fairly close to the top without worrying too much. Here's some info on Fermcap S and how to purchase your own vial.
Advantages to using a keg as a fermenter:
Easy to clean stainless steel
Can handle up to 120 PSI for pressure fermenting
Oxygen free transfers to serving keg
Spunding allows carbonating your beer as it finishes fermenting
Can be used as a uni-tank, serving the beer right from the same keg
No chance of O2 ingress during cold crashing (remove ball lock first)
ClawHammer supply is pre-launching a new 6.5G keg for fermenting full 5g batches. Check it out here . It includes a thermowell and a tri-clamp fitting for O2 free dry hopping and other applications. Pretty good deal for $274.
My typical method for fermenting in a keg also includes serving the beer off the yeast in the same fermenting keg, after cold crashing and settling. I really haven't noticed a yeasty flavor so I figure it's less oxygenation risk and much less effort than transferring to another purged keg. Out of close to 100 batches, I have only tasted what I thought to be autolysis once - this is dead exploded yeast cells, often described as meaty or soup-brothy.
What do you think about this method?
Your Fermentation Method
Bucket or Carboy
PET container
Stainless Steel Bucket Fermenter
Conical Stainless Steel Fermenter
I highly recommend this method for homebrewers just getting started or even for highly experienced homebrewers wanting a very simple method that prevents exposure to oxygen since there is no transfer to a serving keg!