Tying a roast gives it a neat, compact shape and ensures even cooking. While tying is optional with the more expensive single-piece roasts from the loin and rib, it is obligatory for any roast that has been boned or butchered in such a way that it will not hold together on its own. Many markets sell roasts already rolled and tied, but it is a simple enough process to do yourself. First compress the meat into a neat package and tuck in any loose flaps or thin end pieces that would cook too quickly if left out. Then secure the meat with butcher twine tied at 1 1/2- to 2-inch intervals. Finish by wrapping the twine around the length of the roast and end with a secure double knot. After roasting and before carving, snip the strings and remove them.
