I've just started using FF for my layers and now I'm wondering if my batch has gone bad. I keep it all submerged and stir it as often as I can remember, but every now and then it develops a crusty layer of dried bubbles. Is this normal? I've never cared for the smell of it, so I have no idea on how it should or shouldn't smell. I'm not exactly a baker, which means I'm also not used to these smells.