Has this ever happened to you? You shape your burgers into beautiful, perfect patties....but after a stint on the grill, they're tiny compared to your bun, and they've also puffed up into mini basketballs. It's a common problem, but it is possible to avoid it.
The reason burgers tend to puff up during cooking is that the intense heat makes the protein fibers on the outside of the burger contract faster than the inside of the burger, making the center bulge.
The way to avoid it is to make an indentation with three fingers in the center of each burger as you shape them, so they are concave on top. And to combat the shrinkage problem, make them a little bit larger in diameter than your buns.
And while you're doing this, just be sure to use a gentle touch and not handle the meat too much-that can make the burgers tough.
And lo and behold, when the burgers cook up, that expansion at the center gives them a beautiful, even shape throughout.