<< I push the limits with a 55lt keggle. (Avatar pic) Right to the top its probably 57lt. First off: first wort hops seem to tame the froth a bit even a small amount. I batch sparge so get each run off boiling past hot break then add next runnings, repeat etc. This divide's the total hot break instead of getting one big frothy by boiling the whole pre boil volume in one hit (which would definately be a messy boilover) I can effectively get my boiling volume to 1 inch from the brim. (55lt) A spray water bottle there on stand by to shoot down the froth if necessary. I still get the little dribbles down the sides sometimes when I walk away and then smell the burnt toffee "oh ****!" and run back but never any bad boilovers.