Draught (or Draft) beer is almost always un-pasteurized and therefore is more fragile. It should be consumed after being "tapped", and is generally truer to the flavors of the ingredients as pasteurization exposes the beer to heat and changes the flavor profile. Always use brewery approved beer line if you want to have foam free fresh tasting beer. Serving it through a plastic tube from the hardware or discount store or the plain vinyl tubing in your beer tap system you will wind up with a foamy, off tasting beer. Real draught beer is not pasteurized. It must be kept refrigerated between 35F. and 44F. A beer will become wild, turn sour and cloudy in a day or two. Below 44F. a keg of draught beer should last 20-30 days before it loses it's fresh brewery taste and aroma. Craft beers (micro brews) tend to have a shorter shelf life and you should contact the brewery for their recommendations.
Why does my beer foam up?
The 3 most often causes of beer foaming up are:
The temperature of the beer keg
The balance of the draught beer system pressures
The cleanliness of the draught beer system
What sizes of keg is draft beer available in?
The Quarter Keg (Pony Keg) is also used in two variations that are the same capacity but have the slightly larger 17" diameter.
These are the rubber sided version (used by Miller Brewing Company) and the bulged non-straight wall version (used by Coors Brewing Company).