160 degrees Fahrenheit
Checking the temperature of your cooked meat, poultry, and seafood with a food thermometer is the only reliable way to make sure your food has reached a safe internal cooking temperature. USDA recommends not eating or tasting raw or undercooked ground beef. To be sure all bacteria are destroyed, cook meat loaf, meatballs, and hamburgers to a safe minimum internal temperature of 160 °F (71.1 °C). Use a food thermometer to check that they have reached a safe internal temperature. Will a hamburger that is supposed to be cooked medium to well done have any red in the center? In the cooking of beef, the designation medium is generally agreed to have a warm, pink  not red  center and an internal temperature of 140&#176 to 145&#176. The interior of a raw hamburger usually does contain bacteria, and is safest if cooked well done.. Because E. coli is killed at 155 degrees Fahrenheit, the USDA sets the minimum safe temperature for ground beef at 160 degrees Fahrenheit. Destruction of the pathogens that may be present in raw ground beef, particularly E. coli, requires a cooking procedure that heats the beef to an internal temperature of 160°F (20). Use of a food thermometer is the only way to determine that the internal temperature of ground beef patties has reached 160°F (13, 19). (Unfortunately, only 13% of consumers always or often use a thermometer when cooking or grilling hamburgers (9).). Consequently, in June 1997 USDA issued a press release advising consumers to use a food thermometer when cooking ground beef patties, and not to rely on the internal color of the meat. Rather, consumers should cook ground beef patties to an internal temperature of 160 °F as measured with a food thermometer. If uncertain about the temperature reading, take a reading in a second location. Cook ground beef to an internal temperature of 160 °F as measured with a food thermometer. The color of cooked ground beef can be quite variable. At 160 °F, a safely cooked patty may look brown, pink, or some variation of brown or pink.
http://www.healthycanadians.gc.ca/eating-nutrition/healthy-eating-saine-alimentation/safety-salubrite/tips-conseils/cook-temperatures-cuisson-eng.php http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/meat-preparation/ground-beef-and-food-safety/ct_index http://ochef.com/1109.htm http://www.foodnetwork.com/recipes/articles/meat-and-poultry-temperature-guide.html http://www.foodsafetynews.com/2009/08/ground-beef-the-importance-of-safe-handling-practices-and-accurate-final-product-temperature/ http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/meat-preparation/color-of-cooked-ground-beef-as-it-relates-to-doneness/ct_index http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/meat-preparation/color-of-cooked-ground-beef-as-it-relates-to-doneness/ct_index
cooked hamburger temp