Food safety experts always advocate cooking meat carefully–especially ground-meat products–so that even the core reaches germ-killing temperatures. But a new federal study demonstrates that precooking servings to sublethal temperatures before the final cooking actually makes germ killing more difficult.
Food microbiologist Vijay K. Juneja of the Agriculture Department's Eastern Regional Research Center in Wyndmoor, Pa., studied ground beef inoculated with Escherichia coli O157:H7. This bacterium infects a large proportion of cattle entering U.S. slaughterhouses (SN: 3/25/00, p. 199). If it survives to the dinner table, it can trigger lethal hemorrhagic food poisoning (SN: 7/22/00, p. 53).
Using deliberately tainted meat, Juneja made hamburgers and fried them in a skillet until the patties reached an internal temperature of 68C (155F), which took roughly 8 minutes. This killed the E. coli–unless the burgers had been preheated for 15 to