Except for pork, which has to be cooked to a high enough temperature to eliminate any risk of trichinosis, the prevalent opinion up to a few years ago was that most meat needed only to be cooked long enough to satisfy the taste of the diner.
In recent years, however, outbreaks of an infectious strain of E. coli bacteria (E.coli 0157:H7) in ground meats has brought the idea of eating any raw or under cooked meat into question. The USDA has taken a strong position by publishing cooking temperature recommendations that require all ground meat and hamburger to be cooked to 160 degrees, or well-done, and any cut of meat to at least 140 degree, or medium.
In large pieces of meat such as roasts or steaks, the interior portion of the meat is essentially germ-free. Only the surface of the meat comes in contact with the microorganisms such as bacteria, and only a minimal amount of the meat is exposed. In most cooking methods for these cuts, the heat at the surface is high enough to kill bacteria, thus ensuring healthy eating no matter what the internal temperature.
Even low temperature roasting (250 to 275 degrees) provides enough heat to kill food-borne Pathogens. There is always some risk of bacterial contamination, albeit quite small. The USDA recommendations’s are safe if followed correctly.
Ground meat must be cooked at a higher temperature to reach a safe degree of temperature that is needed to kill unsafe bacteria. Each individual particle of meat and fat has been exposed to the air. While the surface bacteria of a steak will be destroyed by cooking, bacteria in the interior of a hamburger can still be viable and dangerous. The USDA recommendation of 160 degrees internal temperature, or well-done, ensures safety. Exposure to 155 degrees for 15 seconds will kill bacteria, and one minute at 150 degrees is also sufficient. The USDA recommendation allows for margin of error.
*****Children and the elderly are especially susceptible to E. coli. Any meat, especially hamburger should be cooked to the USDA guidelines for this age group.