you're right mate, just unscrew slowly and carefully, i've unscrewed too quickly and had a lid fly off cut my finger and hit the garage roof (...hard!) unscrew a bit until it hisses, wait for the hiss to go, then unscrew a bit more until it hisses and wait for it to go, and so on until there is no more hissing.
I'm guessing you have a S30 inlet valve on the lid, have you got a canister? It might be worth at some point swapping the lid for one with a PRV about 5 quid at my LHBS i think???
Back onto the original subject, OB got me onto Bramling Cross, try that with an Eastern Ale

LOVELY