The USDA's guidelines for beef, pork, and lamb have not changed. How safe is it, then, to cook meat as chefs do? Meat that is slightly undercooked by government standards is probably quite safe," says Marion Nestle, a professor of nutrition, food studies, and public health at New York University and the author of "What to Eat" (North Point; 2006). "Even raw meat won't cause problems if it's not contaminated with dangerous microbes," she says. But because there is no way for a person in a kitchen to tell if meat is contaminated, the USDA recommends prudence. The USDA's temperatures actually have a built-in safety margin, Nestle says. Though to chefs pushing that margin, she cautions that the risk goes up the more the temperature goes down. How big is the risk? No one knows, she says.
A greater part of the safety equation than temperature, food scientists say, is whether a piece of meat is intact (a steak or roast, for example) or ground (a hamburger). With intact pieces of meat, pathogens, if present, will exist on the surface, says Dean Cliver, a professor of food safety at the University of California-Davis. The heat of an oven or a hot skillet will kill them before the interior reaches the same temperature. In fact, Cliver says, contaminants are more likely to be transmitted by foods people don't cook at all, such as salad vegetables.
Ground meat is another story. During processing, any pathogens on the surface are distributed throughout the meat. To destroy them, the meat must be completely cooked through to the temperature the USDA recommends.
News about pork is more reassuring. Trichinosis, long a concern associated with underdone pork, is now exceedingly rare, says Jennifer Morcone, a spokeswoman for the Centers for Disease Control and Prevention. The handful of cases that occur each year arise from game meat, specifically bear.
In terms of how to proceed in one's own kitchen, practice may be a person's best guide, Scala Quinn says. "It's about using your senses -- fingers to touch, your eyes to see, and your nose to smell -- to match up with the data the thermometer is giving you," she says, "and then figuring out what works for you."