J and Bob, just so you guys don't think I'm blowing my own smoke, here's part of the article from Meathead's site. Also, do a search for "smoke ring and combustion gas" and you might stumble onto other info online that discusses combustion gas contribution to the smoke ring.
"A faux smoke ring can also develop without smoke if you cook low 'n' slow. When meat is cooked fast, the proteins in the muscle and myoglobin denature at the same time and combine to turn brown. When cooked slowly, the muscle proteins finish denaturing before the naturally pink myoglobin denatures and so the meat remains pink. You can occasionally see this phenomenon in braised meat like a beef stew. It may have been cooked for hours in a liquid at low temps, yet the meat will still be slightly pink inside.
On the other hand, some meats cooked low and slow in a smoky environment in an electric smoker will not develop a smoke ring. That is partially because the wood smolders at a low temp in electrics, and high temps (around 1,200°F or so) are required to create the most nitrogen and carbon monoxides. Experts at cooking in electric smokers add a charcoal briquet as well as wood to create the correct atmospheric conditions for a smoke ring. Some of these briquets actually contain powdered sodium nitrates, which enhance ring formation. But in general, a vigorous charcoal or wood fire at just the right temperature, produces the deepest ring...."
(Taken from the "Amazing Ribs" site)
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