Why do meat patties swell when cooked?

I did a search on this and didn’t really come up with anything. My question is:

Why, when cooking hamburgers at home, do they swell up so they look like tennis balls? Commercial hamburgers are flat, so why do homemade ones become round? Is there a good way to prevent it? I’ve tried indenting the raw patties, which helps a bit.

I used to have a problem with puffy burgers too (I wouldn’t go so far as to say they resembled tennis balls, but they were curvy). My solution was to make sure the pan is hot before putting them on, and flipping only once - and making sure to flip evenly. If you flip too soon, the inside is still raw, the outside is seared, and the expansion of the inside as it cooks doesn’t go evenly. That, at least, has been my experience. YMMV

Oh, and whatever you do, never, EVER squish your burgers with your spatula. That’s just criminal.

I’ve been experimenting with pan heat. I do only flip once, and I try to get even cooking. Any tips on ensuring an even cooking?

Squishing is evil.

I think it’s uneven contraction as they aren’t expanding at all. Odd but I never get that on a grill.

My approach for even cooking is to watch the “Cooking line” on the side of the burger - as you cook, you’ll notice that the brown cooked part creeps up on the upper pink, raw part… As it approaches the half-way mark (but not quite), that’s when I flip, and repeat the process until the outside is uniformly brown. I guess a big part of the trick is finding the temperature that is hot enough to give the right texture on the outside, but not so hot that the outside is charcoal while the inside is still tartare. What that temperature is, I have no idea. I’m one of those people that doesn’t measure anything. Which is why I can’t bake.

Use a pan with a heavy bottom or a cast-iron skillet. Thick-bottomed pans distribute heat much more evenly than thin ones.

I’ve been using my electric skillet. Should I go ahead and spend the money to invest in a cast-iron skillet? I’ve been wanting one for a while.

lol, the things arent expanding per se…

the edges cook faster than the inside, so it contracts, making the inside pouf out in response to the squeezing. Cooked meat is compressed because the proteins are coagulating and the water/juices are being squeezed out=)

Make your burger patties dished in the middle and they will end up the same thickness throughout when you are finished=)

Let me see if i can find the link i want…<rummages on the internt>

hmm, here is quote))

Grilling Great Hamburgers
Burgers often come off the grill tough, dry, and bulging in the middle. To our surprise, making a shallow depression in the center of the patty was the first step toward a great burger.
The challenge: Upon deciding to develop a foolproof method for grilling burgers, we knew straight off exactly what we did not want: that all-too-familiar backyard burger that’s tough, chewy, and dry, with at least half of the crust torn off and left stuck to the grill. What we did want was a moist and juicy burger, with a texture that is tender and cohesive, not dense and heavy. Just as important, we wanted a flavorful, deeply caramelized reddish brown crust that would stick to the meat, and we wanted a nice flat surface capable of holding as many condiments as we could pile on. Given the vagaries of a live fire, we knew it would be a challenge to hit all of these marks.

The solution: What we first discovered is that the kind of meat you use to make a burger matters. Almost every recipe we looked at recommended chuck as the cut of choice for robust flavor and juiciness. Most recipes also suggested starting with a chuck roast or large steak and asking the butcher to grind it up as opposed to buying preground beef. Testing bore this out. It also taught us that for optimal flavor and texture, the ideal ratio of fat to lean was 20 percent to 80 percent.
Our next tests concerned burger size and shape. Too thicK-anything over 1 inch-and the burgers were tough and chewy by the time they had cooked through. What ended up giving us the best results was a “sunken” burger, with a rim about 3/4 inch thick and a center area about 1/2-inch thick. The reason for depressing the center is to eliminate the puffing that otherwise occurs when burgers cook. The thinner centers on our burgers do puff, but only to the level of the 3/4-inch outside rim, thereby producing a perfectly flat burger able to contain ketchup, onions, and more.
As for grill heat, most recipes recommended a high level to allow for development of a flavorful crust. We thought this might be too much for our relatively thin burgers, and we were right. It was too easy to overcook the burgers on a blazing hot fire. Medium hot did the job, producing enough heat to nicely sear the crust while also providing a wider margin of error during which to cook the center.

For good measure: Lots of people try to hurry burgers along as they cook by flattening them with a spatula. Unfortunately, this serves only to squeeze the juices out of the burger. We recommend that you use the spatula for flipping purposes only.

They’re not at all expensive – at least not around here. I bought mine at Target for $10. It’s awesome. I always think it’s worth having one good cast iron skillet around the house. I say buy it. Properly season it, don’t wash it with soap or abrasives, and don’t cook anything (too) acidic in it, and it’ll remain stick-free and last you a lifetime.

i’m a heathen: i think the only proper way to cook a burger is on a grill.

aruvqan - if you’re going to use an quote that long, you might consider using a link instead, to make sure you don’t run afoul of the SDMB’s policies on copywrited material.

(Apologies for being a Junior Mod ™ - can’t remember whether making a correction such as this is currently frowned upon or not.)

Smoosh 'em flat and cook 'em on one of those indoor grills sold by former boxers. takes 5 minutes and comes out quite tasty. And you can stack 'em if you want them thicker.

This is right: make a normal-shaped burger, then thin it in the center - sort of like a red blood cell. As it shrinks during cooking (from the outside in) it assumes a desirable shape.

If you want consistent rave reviews for your burgers, grind your own meat.

Places like McDonalds have clamshell grills which sandwich the patty inbetween two hot plates. Clearly this is not a solution for the average home cooker. At some restaraunts I’ve seen a sort of metal press or weight of some kind that has been left to heat up on the grill (flat frying grill, not the open flame sort) and is placed on top of the patty, presumably for a similar reason.

I don’t know how BK or Wendys does it.

You can also use a heavy metal square with a grip on one side: You set it on top of the burger while it is grilling and it keeps the burger from swelling up. Also good when frying bacon, etc. You can get them at William & Sonoma for 20-30 bucks, or make one for a buck or two.

I believe another secret of the flat McDonald’s hamburger is that it is frozen. To make a flat McDonald’s like burger cut a sour cream container (or similar) in half to make a ring mold. Place the hamburger in the mold and compress flat with a plate or your hand. Make sure it is compressed tightly. Freeze the patties then place the frozen patty in a skillet or on a griddle. This is the important part- Sear the pattie to the bottom of the cooking surface by placing a plate on top and applying even pressure. Flip when the top of the patty appears red and slightly thawed. Flipping may be a little tricky because of the sear, a sharp edge on the spatula helps. Do not sear the second side! Cook to desired doneness.

I’ve noticed that ground meat seems to have something of a shape memory; if you take a handful of mixture and first roll it into a ball, then briefly squish it to make a patty, it will try to revert to a ball shape when cooked - if you just take a handful and sqush it flat, then pat the sides all round with a palette knife to make it roughly circular, it stays much flatter.

Well, I’m currently devouring my latest attempt at burgermaking. Based on Mangetout’s suggestion, I didn’t ball the meat up before flattening. It definitely helped, as did cranking the heat in the electric skillet.

Thanks, everyone, for all your suggestions and advice.