Opened up a bottle of my latest brew last night and found it was a bit of a gusher. The others in the batch have been fine so far, so this leads me to believe that the bottle must have had a little crud left in it. What I don't quite understand, however, is why does this make a difference? What I mean by this, is how does having a little (and it will have been tiny) amount of stray yeast make such a huge difference to the carbonation levels? Is it the mix of different yeasts that make it go wild? And, if the sugars have fermented already, what is it feeding on to create such activity?