OT, but from my experience the cause of boil-over is the telephone (or anything else that takes your attention away from the brew pot). I have had boil-overs after adding the remaining extract. Watching the brew pot and riding the temperature/flame when it looks like it's about to boil over is the way to avoid it. It will usually only (try to) boil over once. When it foams up, the proteins coagulate and it settles down again. Yesterdays batch and the one I'm cooking up today I'm trying FermcapS. It went great yesterday, no threat of boil-over.