Does searing meat at a high temperature when you first begin to cook it help to seal in the meat's juices, flavors, or nutrition?
Many of us would probably answer yes, but it's just not so according to science writer Harold McGee.
In his excellent volume On Food and Cooking: The Science and Lore of the Kitchen , he exposes this as a kind of urban cooking legend, with no basis in scientific fact.
The legend started, perhaps, with Aristotle, who wrote that "as the exterior pores contract, the moisture contained in the [meat] cannot escape." The legend was revived in the nineteenth century by German chemist Justus von Liebig. Liebig believed that most of the nutrients in meat were water soluble, and that they would bubble out if the meat dried as it cooked.
Searing, he believed, formed a kind of waterproof shell which held in the meat's juices. Liebig's theories became instantly popular, and they can be found in most major cookbooks through the beginning of the twentieth century.
Actually, these theories have little to do with reality. Meat's nutrition is not water soluble. Even if it were, the crust that forms on seared meat is far from waterproof. In fact, a study done in nineteen-thirty found that seared meat actually lost MORE moisture than meat cooked at constant temperature.
Is there any reason to sear your meat? While searing won't lock anything in, it will brown the meat more thoroughly. If you enjoy the well-done flavor of browned meat, then sear away. Remember, though, that you're adding a flavor, not preventing one from escaping.