I rehydrated the yeast(Danstar Nottingham,this stuff settles out well and compacts down really hard) in 400ml of cooled wort that had been taken from the boiler 10 minutes into the boil.The yeast was quite active when i pitched it into the main brew.Within one day a hard looking brown crust appeared over the wort and has remained in place ever since,a few white patches of yeast head broke through but that was all, is it safe to skim this brown crust from the wort


