Why should hamburgers be cooked to medium well, but steaks can be cooked to rare?
Today, I visited a Family and Consumer Science Class and demonstrated to them the answer to this question with play-doh. (I had to fight the little Daughter at the Meat Counter off the play doh.) I took some pictures to share on my blog.
When steaks are cut, there is a possibility that bacteria (disease-causing germs) could be on the surface of the steak. Steaks (and roasts, too) are whole-muscle cuts, meaning that they have been cut into serving- or cooking-size pieces, but the internal portion of the cut is still undisturbed. So, those bacteria are going to only be on the surface of the steak, and when you cook it, the surface will be the first to get hot and it will get the hottest. Any bacteria on the surface are going to be killed in the cooking process. The internal part of the meat does not have to get hot enough to kill any bacteria. So cooking steaks to rare or medium-rare is perfectly safe.
Ground beef is made from smaller cuts of beef that are trimmed away from the steaks and roasts. They are not lower quality or inferior in anyway other than they are too small or too tough to make good steaks are roasts. (Actually, which parts are cut into steaks and roasts and which parts are ground into hamburger is largely driven by ground beef demand. People like hamburgers.) These parts and pieces (trim) are kept in large containers and transported to the grinding room in the plant. All of these little pieces could have bacteria on their surfaces just like the steaks above. Several companies have researched different ways to treat the trim pieces to lower the bacterial count on the surface.
Here is my play-doh trim. It’s smaller and cut into irregular pieces. The bacteria are still only on the surface.
Here is where the difference is. The trim is ground. When meat is ground, it is pushed through a metal plate with small holes. Behind the plate, is a rotating knife that cuts the meat and allows it to be pushed through the plate.
This is not play-doh. I actually have pictures of real meat! Yay! You can see the round strands of ground beef coming through the plate.
Now, any of those bacteria that were on the surface of the meat are mixed up and spread all throughout the ground beef. When we make patties out of the ground beef, the bacteria could be on the surface or anywhere inside the patty.
These are some patties we made for a research project. Real bacteria don’t have color and you can’t see them on or in your patties.
So, when you cook patties, you should always cook them to 160 °F. USE A MEAT THERMOMETER. Make sure the thermometer is inserted into the middle of the patty.
When you order hamburgers at a restaurant, ALWAYS order them to medium or greater.
If you have other questions about food safety, I wrote a blog post about food safety in September.
A common conversation over steak dinners with meat scientists is how we order our steaks. I order my steaks cooked to medium-rare. Why, you ask? Well, there are two main types of protein in meat that affect tenderness, connective tissue (holds it all together) and myofibrillar (causes the muscle to contract). These two proteins react differently to exposure to heat. Connective tissue (collagen) protein dissolves to gelatin when it is heated, so it becomes more tender. The myofibrillar proteins harden as they are heated and become tougher. The optimum combination of collagen dissolving and myofibrillar hardening happens at about the temperature of medium-rare. Yum.
Some people don’t like the serumy (bloody) flavor associated with medium-rare and they want their steaks cooked longer (my mom). I guess that’s ok. If you like more well done steaks, I suggest you buy steaks with more marbling (USDA Choice, Prime, and Certified Angus Beef). The extra marbling protects the tenderness of those steaks when you cook them more.
Like I said, there is really no wrong answer to the question, “how would you like your steak cooked?”
However, you must cook hamburgers to medium (160°F) or greater.