So how do bottles differ from kegs? If bottled properly, they really should have similar storage properties. The big difference with bottling a five-gallon batch versus kegging a five-gallon batch is roughly 48 bottle fills compared to one keg fill. A keg is easy to painstakingly fill. A keg can be filled to the brim with water and then completely filled with carbon dioxide by pushing the water out of the keg with the gas. Then you rack the beer into the CO2-filled keg, essentially eliminating any possible contact with O2. Oxygen pick-up is a non-issue using this method. The other thing about a keg is that you don’t have to pull the fill tube out of it, thus exposing the beer to the environment, like you do with a bottle filler.
When you bottle, you may have some bottles that are about as low in oxygen as the keg and you probably will have others with higher levels. This results in variability within the batch — some will taste great after two months and some may taste oxidized. Of course, the real joy of bottling is convenience and the added flexibility of sharing your brews without having to bring your friends to your keg or hauling your keg around town!
Whether kegging or bottling, beer will not have any sort of shelf life if the key principles of sanitation, good yeast, healthy fermentations and careful racking practices are not used. Beer contaminated with bacteria or beaten up by sloppy racking practices is doomed. For those brewers who filter, this practice can do much more harm than good if proper filtration techniques are not followed. If everything is done correctly up to the point of filling, you will have maximum shelf-life, provided you use filling techniques that minimize oxygen pick-up and then store your bottled or kegged beer cold.