Yesterday I smoked with applewood for the first time (lamb baby back ribs, 4-hour cook, 2-hour smoke, 225F per Auber PID). This morning I noticed a lot of black residue on the "approach" slide - the hotplate was clean. When I brought the generator in to clean the slide I saw that the residue was not smoke stain, but 3/4" of crusty char, right behind the gap between the approach slide and the hotplate. It required a knife to scrape it off.
Is the applewood particularly "sappy" or something? No similar problems with hickory or oak.