Today I've had to change a part filled lager barrel because it went flat and had a tang to it. Put a fresh one on and same happened after about 20 pints.Checked the gas, it was fine, and called out the engineer. He's just been and said there's nothing wrong in the cellar, its the batch of lager. So for all you in my area the batch date is 7/3/11. Mine is a lager pub so I've turned many a customer away today. .