There is a science to barbecuing! There’s an explanation for why food browns during cooking, why the smoke ring appears on barbecue, and why some cuts require higher internal temperatures before it's tender.
The browning can easily be explained by the Maillard Reaction. This reaction causes the amino acids in foods to react with reducing sugars to create the brown cooked color of foods.
The smoke ring can be explained by the chemistry of nitric oxide from burning wood combining with myoglobin in meat to form nitrosyl hemochromogen. This is the same pigment found in cured meats. Meats cooked in the oven don’t do this since there is no source of nitric oxide in this environment.
Briskets and pork butts have a high percentage of connective tissue containing collagen. Collagen is converted to gelatin when heated, and it requires a higher internal temperature to achieve this. The muscle fiber component of tenderness gets tougher as internal temperatures go up, while the connective tissue component of tenderness becomes more tender. Fall-apart barbecue is achieved because the connective tissue has become soluble with cooking."