When forming hamburger patties, I was always told that you had to make a shallow indentation or dimple in the middle of each patty — this would keep the center from bulging up as it cooked so that the patty would stay flat and even. I never questioned that technique until I came across even more methods on how to do this, so I just had to test them out myself! The basic theory is that as meat cooks, the proteins contract so that the whole patty shrinks and puffs up in the middle.
