[brewmonkey]

I guess I should have added that with the bigger beers like the Imperial's and Barleywines that they can and should be cellared like good wines as they will continue to develop as they are generally bottle conditioned.

Bottle conditioning is a process in which the brewer introduces a small amount of yeast back into the beer at packaging time which will continue to ferment and carbonate the beer. Having this in there will also reduce oxidation that may have been picked up at bottling (called airs) as yeast metabolizing sugar produces CO2 as well as alcohol. While it will not increase the alcohol content much when the CO2 is produced it will not be able to escape, and therefore will force itself back into solution creating the carbonation.

Some beers (like AB or Coors products) are carbonated artificially by pumping CO2 thorugh a diffuser (porous ceramic stone or sintered stainless steel) that works in the same manner. When the CO2 goes into the beer it will go through the beer and escape into the headspace in the tank. When the headspace is filled and the CO2 can no longer escape it is "forced" to stay in solution and gives carbonation to the product.