my first batch ever. a milk stout with chocolate and vanilla. when i opened the bucket after a week to check the gravity, i was eye to eye with this. i was a bit panicky during the brewing process because i lost power (hurricane Irene) in the middle of the boil, so many mistakes could have been made. that thing floating on top was probably 1/8 inch thick, crusty, and would break apart and sink when disturbed. i have moved it to a secondary, so i could start another batch with no modifications or complications. the smell was fine and it tasted quite good, which leads me to believe its ok, i was just wondering what the heck was on top.