Have had this happen with a few aggressive yeasts/starters. One suggestion on the aluminum cap - I fold a square or almost rectangular piece of aluminum foil (say 8 x 11') over until it forms a square so it has a bit of thickness to it (around 3x3'). Spray it good with Star San while flat and then form it over the top of the flask and down the neck. When you grab the flask to stir the starter prior to placing it on the stirplate if you grab the foil and inch or so from the top of the flask around the neck this loosens up the foil but retains a barrier so that you perhaps won't get as much of a mess from the krausen. This has worked well for me. Montanaandy
