Originally Posted by britjh22
I'm betting he is seeing it on the top of his foil, and therefore it wouldn't/shouldn't be residue up there. I see this occasionally too, haven't worried to much yet.
Why shouldn't it be up there? Here is a little experiment for you guys. Try lathering just the bottom of the foil with molasses, poke holes through it, and put some coals on there. You will get those "burn holes" on the entire surface of the foil and a lot more residue on the bottom.
Aluminum foil burns at 660 degree Celsius. If your coals produce that much heat your house would be on fire.