Just over 8kg from memory. I have never done this much before so I am guessing on how close to the brim it will be. Just did the rough calculation and that's only 21L of mash water. So in total it won't even go over the 30L mark in the tun, which won't be an issue at all. I remember calculating that it would be pretty touch and go but it looks like there will be plenty of room, unless I am wrong about the 8kg (don't have the recipe at hand)...