Keg beer has enemies? Who are they? How dare them! It's a tough life to be beer. If all goes well, beer gets to leave the brewery (or home brewery) in a nice fresh clean keg and then it is up to us to keep it that way. It seems to be easy for a keg of beer to go bad, so who's to blame? Here they are, the guys that spoil it for everyone.
BEER LINES - Bacteria, wild yeast and beer stone (scale left behind by some line cleaners) can cause "off flavors" or shorten the shelf life or spoil an entire keg of beer. As beer is dispensed it runs into these undesirables in the beer line and changes the flavor of the beer and in some cases ruins it. Make sure to clean your beer lines after each keg and replace your beer lines every 6-8 months.
TEMPERATURE - Keg beer in fluxing temperatures and changing environments can easily turn bad. Oxygen reactions are increased in hotter temperatures as well as wild yeast and bacteria replication rates (if present). Steady temperature is #1 when it comes to a beer's shelf life. As temperatures rise and fall the beer staling reaction rates go up and the beer aroma, flavor and finish all suffer. Keep your keg beer at a constant temperature with a kegerator.
AIR - Air is full of dust, bacteria, wild yeast and the worst of all... OXYGEN. Beer hates oxygen. They don't do well together. You could say they are mortal enemies. Yeast take in almost all the oxygen during the fermentation stage and beer wants it to remain this way. The smallest hint of oxygen being introduced to the beer, at any stage of the process, is enough to cause damage. If you use a hand pump, which uses outside air instead of CO2 to push the beer from the keg, you can only expect your keg of beer to remain fresh for a day. Always use food-grade CO2 or Nitrogen to dispense your beer. It will last much longer.
TIME - Unlike wine, beer doesn't get better with age. Keg beer can stay fresh for 30-40 days when all the variables are controlled. Beer is best consumed fresh. Over time the hops fade, malt loses its clarity any trace bacteria or wild yeast that may be present will take a stronger hold. Age your whiskey and balsamic vinegar, not your beer. Mmmm whiskey.
KEG COUPLER - A dirty coupler check ball and retainer can often go overlooked. They usually don't get any cleaning until the check ball decides to become stuck one day forcing you to take the coupler apart for cleaning. A dirty check ball can throw some unpleasant flavors in the beer as it travels towards your glass.
CO2 - Use only food-grade CO2 from reputable filling stations. Paintball CO2 recharge stations and other non-food related CO2 filling stores mix oil with the CO2 to lubricate machine parts. The result is some unpleasant metal tasting beer.