Originally Posted by wild
Aren't cask ales fully naturally carbonated then vented 24 hours prior to serving with a vented spile to bring the CO2 levels down?
That's OK if you drink the beer all in one go or within a day or so. The problem is with a keg that gets consumed at a more leisurely pace over several weeks or months.
1) the beer will slowly go flat- really flat
2) there is the risk of oxydation as air enters the keg to replace the beer
Giving it a little blast (1 or 2 PSI) of CO2 is a good compromise.