Ah, sour beer - the memories...

Years ago, I was in a pub in Manchester which shall remain nameless, and saw a sign up saying the guest beer was half price. Naturally I went for it (it was a beer I liked, which was a bonus). I got it back to my table and... hmm. Bit on the flat side... bit on the sour side... actually a lot on the sour side... Actually who am I kidding, this beer's gone.

So I took it back to the bar and told the pimply youth who was minding the pumps that the beer was off. "Yes," he said, "that's why we reduced it."

True story.