For anyone who likes their beer, in CZ beer from tanks as opposed to portable barrels is regarded as the way to store beer so that it is in the best condition possible when served. There is a bladder/diaphragm inside the tank. Air is forced into the tank one side of the diaphragm, which pushes on the beer and forces it out to the tap. This way no air or gases come into contact with the beer. Similar to a giant expansion vessel for any plumbers out there.
That's interesting, I've had three tours of St Austell Brewery, it's half a mile from me. On one tour the bloke explained that it was oxygen that degrades beer, hence a barrel will start to degrade after 3 days and is pretty much knackered by 5 days.
The best Tribute I've had has been from the brewery and this same bloke told me they change it every 7 days wether it's needed or not. I tackled him on the oxygen story and he said at the brewery they use nitrogen (I think), I said so why don't all pubs use it. cost he said.