I'm not sure what that stain is, but it liquefies when it gets hot. I noticed it after removing it when it was facing the coals, so I don't think it is grease. I'm a little concerned that it may be affecting the flavor of the food and I'm not sure how to get that off. The other side had some charred-on brisket drippings that I was able to scrape off. I'll foil it from now on. Just wondering because the plate setter doesn't smell that great.