I brewed my Chocolate Stout on Monday and checked the fermenter this evening. The airlock is bubbling like crazy but no krausen has formed. Is this a cause for concern? Usually I have a krausen. The main difference in the linked recipe is that I switched from nottingham to WLP001 (which is a re pitch from a pumpkin ale) and I am fermented kind of on the cool side (64ish). Any thoughts?