http://www.fsis.usda.gov/factsheets/doneness_versus_safety/index.aspDoneness Versus Safety
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FSIS reports that even if hamburgers look fully cooked, one in four hamburgers may not be safely cooked. Yet only 6 percent of home cooks use a food thermometer for hamburgers and only 10 percent use a food thermometer for chicken breasts, according to the latest data from the Food Safety Survey, which was conducted by FSIS and the U.S. Food and Drug Administration.
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Beef
Beef roasts cooked to 160 °F will generally have very little pinkness to the meat, and the juices will not be pink or red. Below the temperature of 160 °F, the center of the roast will be pink or red, depending on the internal temperature. A beef roast cooked to 145 °F in the center can be considered safe since the exterior of the roast would have reached a temperature high enough to destroy bacteria, unless it is a rolled roast or one that has been mechanically tenderized. A consumer would not be able to determine if a roast that was pink in the center had reached the safe temperature of 145 °F without a food thermometer.
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Ground Meat and Poultry
Research indicates that the color of the meat and the color of the juices are not accurate indicators of doneness. Ground beef may turn brown before it has reached a temperature at which bacteria are destroyed. A consumer preparing hamburger patties and depending on visual signs to determine safety by using the brown color as an indicator is taking a chance that pathogenic microorganisms may survive. A hamburger cooked to 160 °F (165 °F for ground poultry), measured with a food thermometer throughout the patty, is safe — regardless of color.
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