Any good smoky cut of meat has a good smoke line (or smoke ring) but where does it come from and what reactions form it? More importantly, is it really a sign of good meat?
Fire up the charcoal and wood that you've chosen, and get that fire cozy at about 220-250 degrees. Once you set the meat above the fire several things start happening. Steel Town BBQ explains it scientifically. "Nitrous oxide (NO), a gas, is being produced by the combustion of the wood. Nitrous oxide is a relatively unstable molecule and in the presence of heat and oxygen is oxidized to nitrous dioxide (NO₂) As the NO₂ passes over the moist meat, it comes in contact with water forming nitric acid (HN03). The acid dissolves on the moist meat surface and forms a nitrate ion (N03⁺). This nitrate then combines with the myoglobin forming a pink compound. This myoglobin – nitrate pigment is responsible for the “smoke ring” found in barbequed meats. The smoke ring is generally only ¼ to 3/8 of an inch think. The depth of the smoke ring is limited by the ability of the nitrate ion to penetrate the meat and by the temperature of the meat.
Southside Market Brisket (from Boots in the Oven)
"Myoglobin proteins begin to denature (break apart) at about 120°F. Denatured myoglobin is no longer able to combine with the nitrate to for the pink pigment. It is important to remember that the formation of the smoke ring occurs early in the barbeque process and its maximum development requires plenty of oxygen (air) at the fire, moisture on the meat and relatively cool meat surface temperatures." I couldn't have said it better myself.
So basically, it takes a well controlled fire and moist meat to get that smoke line, and while it doesn't necessarily mean the meat will be good, it is a sign that the it was cooked low and slow which is probably going to make for better than average results.
- BBQ Snob