Via huffingtonpost.com:
What causes a “smoke ring” to form around smoked meats? If you’re not familiar, a smoke ring is a region of pink colored meat usually seen in the outermost 8-10 millimeters of smoked meats. You can see the pink zones on the pork rib pictured above and below, as well as a distinct pink color near the edges of the pulled pork shoulder in the bottom photo.
A pink (or red) color in meat usually indicates the presence of myoglobin. Myoglobin’s reddish pigment is usually lost when meat is cooked because the heat causes it to denature and turn brown. The center of a rare steak remains red because it never reaches a high enough temperature to denature the myoglobin. However, the outside of smoked meat gets extremely hot over the course of cooking, so cool temperatures can’t be the cause of the pink color in smoked meats. What else might cause myoglobin to stick around, despite the heat?
