I've been brewing for a bit more than 18 months, just over 12 months all grain. I've got a few beers now that I've kept for a while - I opened up a porter that I've had for a year tonight, and got a couple of bottles of last year's Xmas brew saved up too. I've found that when I open them up they fizz up a lot. Not immediately, not explosively - there's a small delay and then they foam like hell. Even when very well chilled this happens. They taste largely fine, though there is a very mild flavour that I've started to notice in all my brews. It's very hard to pinpoint and describe but I thought it was maybe my water (London water) so I had started to try things out with water treatment - no success in getting rid of it. It's been there since my first AG brews but I didn't notice it until I'd done a few. Some of my recent brews are also turning out pretty fizzy, though it takes time to set in; the first few bottles are fine, but then as the weeks go on they start to fizz like mad when I open them. Does this sound like an infection of some kind??? Some kind of wild yeast that's got in maybe?