Some people ferment in them, but that really is a minority. Most people just transfer fermented beer into them for serving.
The top of a keg looks like this:
That top pops out, and has this big rubber O ring like this:
Just closing the lid won't create a good seal, so you have to apply pressure (via a CO2 tank, with a regulator) to "seat" the lid. The pressure pushes the lid up, the O ring makes the seal.
They are stainless steel, and extremely easy to clean.
The biggest advantage is that you don't have to bottle anymore. You can also fine tune your carbonation level, and also pour a pint whenever you want one.
Disadvantages are cost (kegerator, CO2 tank, regulator, lines, taps etc), and the space the kegerator and extra kegs takes up.
This is a good
basic kit
I ended up upgrading to the
2 keg, and dual body regulator kit. The dual body regulator means you can have 2 kegs at 2 different pressures. Otherwise, with 1 body, even if you split the line, every keg you hook up has to be set at the same pressure. This isn't advantageous if you want to carbonate one beer, which requires higher pressure, and serve another, which requires lower pressure.
