SOUR BEER may sound a little redundant. Beer is after all fermented, i.e. soured, in the first place, so you may ask what the difference is between a sour beer and regular beer. You might also ask why, if there is a difference, anyone would want to drink something that is soured. No one likes sour milk, so sour is a bad thing, right? Like so many things in this world, reality is much more complex than names express.