Has been a while since I last cleaned out my freezer - today I thought I'd give the seals a wipe and they were really black. It came off straight away with an antibac wipe. Is that mold or just general grime? I have a tonne of breastmilk in bags in that freezer and I'm a bit concerned about whether I'm still okay to use it? Yes the bags are technically sealed so any spores hopefully haven't got to the milk yet but I have the bags in the freezer loose and to get the milk out of the bags once defrosted the milk has to pour out of/ touch the top of the bag? Thanks - please advise as I don't want to give him something unsafe but also don't want to chuck the milk unncecessarily!