Originally Posted by Rainee
Smoke rings are produced by a chemical reaction between the meat and the penetration of the smoke. You will see a smoke ring on meat barbecued over a wood fire. It is a pink color that extends from the outside surface into the meat. It's thickness is dependent on several factors, such as the type of smoke and the duration of smoking. See the following section about chicken for a better understanding of the chemical reactions involved.
smoke has a reaction with the chemicals in the bone and meat. The meat turns a pink color even though it is thoroughly cooked. Ash is loaded with potassium and sodium nitrates. This reacts with oxymethyglobin to form nitrosaminoglobulins and gives us the pink color of hams, lunch meats, hot dogs, and smoke rings.
Rainee is right on. The nitrates in smoke react with the protein in meat, turning it a pink color. Sodium Nitrate (saltpeter) is used to preserve foods, and will also turn meats cured with saltpeter pink, i.e.; ham, hot dogs, salami, corned beef, etc.
Artificial smoke rings can be created, buy using a nitrate compound in your rub. I don't do this.
Usually, a sign of good BBQ is a pink ring penetrating deep into the meat. On my pork butts, this pink ring is usually 3/8 - 1/4" deep into the meat. I've seen a 1/8" deep pink ring on smoked turkey legs, and the chickens I did last weekend, although the breast meat didn't have a pink ring, the legs did. The legs also stuck out from the main body of the bird more, and thusly, were more exposed to the smoke.