Why should you rest meat after cooking it?-- Darren
Resting meat serves three purposes. First, it allows the meat to finish cooking through, Straight out of the oven, or off the fire, the outside of a piece of meat is hotter than the middle. The difference in temperature can be quite large. During resting, the heat from the outside penetrates to the middle, finishing the cooking of the interior. That is why many recipes call for taking a roast or whole bird out of the oven when the temperature read on a thermometer stuck into the middle of the meat is actually a few degrees lower than what is desired. The meat finishes cooking outside of the oven because of the carry over cooking.
Second, allowing meat to cool allows the collagen and connective tissue to firm back up again, making slicing easier. See the posting Slicing Roast Beef, where this was discussed.
Finally, according to Harold McGee in On Food and Cooking , as the meat cools, its water-holding capacity increases, meaning that less juices will be lost during cooking or drain out of the meat once it is on the plate.
The length of time that the meat should rest depends on the type of meat and its thickness. For smaller pieces of meat 5 to 10 minutes may be enough. Large roasts may be rested 1/2 hour to a full hour, or sometimes even longer for very large pieces.