Why is it safe to eat roast beef medium-rare, but not hamburger?

During the cutting and wrapping of meat, the meat may come in contact with bacteria that is on the butcher’s knife, counter, hands of the handler or anything that it touches. We can help to prevent this by keeping all surfaces clean and sanitized, but even then it is hard to completely prevent.

With a steak or a solid piece of meat such as a roast, the bacteria will only be on the outside. They cannot chew their way through a cut of meat so they cannot get inside a roast or steak unless we let them hitchhike on a fork, knife, thermometer or grinder. Cooking or grilling the surface of the meat until well done, will kill the bacteria that may be there. If we are careful, there won’t be any bacteria on the inside and so it is okay to cook the inside to a less than well-done temperature.

With ground beef, the grinder will spread bacteria from the outside to the inside of the meat. It is especially hazardous because of the many, many surfaces in the ground meat, each of which may carry bacteria. That is why ground beef must be thoroughly cooked all the way through to the centre to a temperature that will kill the bacteria, which is 170°F (77°C). Because patties are too thin to accurately measure them with a thermometer, they should be cooked until the juices run clear. Cut them open to see inside. If they are still pink, they need to be cooked longer.

Other meat safety tips:

  • Using tongs or lifters to turn the meat, instead of a fork that pierces, will keep dangerous bacteria on the outside until the heat of cooking destroys them.
  • Roasts that have been boned, rolled or stuffed may have bacteria on the inside because of the butcher’s knife or skewer transporting harmful bacteria to the inside. These cuts need to be cooked thoroughly to the well-done stage.
  • Thermometers can carry bacteria to the inside. Sanitize the thermometer before using it and insert it after the heat of the oven or grill has destroyed the bacteria on the surface of the roast.
  • Partial cooking followed by a finishing stage at a later time is a risky practice. Partially cooked food may feel hot on the surface when we touch it. But, in fact, it means we have warmed the inside of it to the bacteria’s favourite temperature and softened it making it easier for them to use. This allows bacteria to grow to dangerous levels. For example, if a roast is started in the oven or if ribs are parboiled for finishing on the barbecue, they should be placed on the barbecue immediately after coming from the oven or pot.
  • If you use a brush to baste raw meat at the beginning of your cooking period, the brush becomes contaminated with the bacteria from the surface of the raw meat. If you baste the cooked, ready-to-eat meat with that same brush, you will recontaminate the cooked meat. Use a clean brush for cooked foods.
  • Platters and utensils used to carry food to the barbecue will be contaminated from the raw meat. Do not use them to carry cooked food off the grill, use a clean platter and utensils.

Source: Everybody’s Food Kitchen by Sheri Nielson, 1996.