This has been a persistent problem that I am at my wits end to solving. My seconday keg fermentation takes place at about 15degC or about 63F and when the beer is siphoned in at the start it is always lively with nice dissolved CO2. Then I leave it to mature for about a month [I prime with 2-4oz of sugar or syrup] and when I try the first pint it has gas in it but not as much as the amount of dissolved gas which was in the beer when i siphoned it into the keg 4 weeks ago. Despite replenishing CO2 from a cylinder the beer just seems to get more and more flat. When i keg I also put about 10 pints into bottles with very minimal priming sugar and this is completely fine - bright with a nice amout of gas. I am srupulous about cleanliness, temperature control but I just can't seem to get round this problem. It is so disheartening - I have a brew just 5 days fermenting in the plastic bucket [at 15C] and last night a drew off a pint of it to try and in spite of the slight yeast taste [I use Fullers yeast which I harvested from one of their beers] it had the perfect amount of dissolved gas in it and a more 'pubby' fruity satisfying beer taste than the beers I've got which come out of the keg and i know that once i keg this one it will go exactly the same way as all the others - flat and duller and duller as the weeks go by. Why is this? Comments and advice gratefully received.