I learned something new over the weekend...if you're brewing ale you need to make sure that you leave enough head space in the top of the fermentor for the crausin (spelling), yeast cake, to fully develop without running out the airlock. the reason has to do with layering of yeast and the way they feed and develop flavors. if you fail to do so you'll end up with a wierd kind of lingering soappy yeasty taste in your mouth. this is most noticible in hefewiessen or other beers drawing most of thier flavor from yeast. just passing the knoweldge along to everyone.

Generally I start a 21litre brew in a 30litre tank even though the krausen usually is only a few inches high, then I move it to a snugger 25litre tank to minimise the amount of air its close to. I didn't know what would happen if I filled it to the top, best I don't find out sounds like.