To prevent hamburgers from puffing up during cooking, many sources recommend making a slight depression in the center of the raw patty before placing it on the heat. But we find the need for a dimple depends entirely on how the burger is cooked. Meat inflates upon cooking when its connective tissue, or collagen, shrinks at temperatures higher than 140 degrees. If burgers are cooked on a grill or under a broiler, a dimple is in order. Cooked with these methods, the meat is exposed to direct heat not only from below or above but also on its sides; as a result, the edges of the patty shrink, cinching the hamburger like a belt, compressing its interior up and out. But when the patty is cooked in a skillet, as in our recipe for Juicy Pub-Style Burgers, only the part of the patty in direct contact with the pan gets hot enough to shrink the collagen. Because the edges of the burger never directly touch the heat, the collagen it contains doesn't shrink much at all, and the burger doesn't puff.
DIMPLED FOR GRILL AND BROILER
NOT DIMPLED FOR SKILLET
Don't bother "dimpling" burgers cooked in a skillet. Unlike burgers cooked on a grill or under a broiler, their edges never get hot enough to shrink, pushing the interior up and out and resulting in a puffy patty.