Roasting is a dry-heat cooking method that uses intense oven temperatures to cook meats or vegetables.
Roasting for meats and vegetables are actually two different "principles" of cooking. With meats, in order to create the ideal edible, the meat is cooked at two different temperatures, one to create a crispy crust on the outside, and another to cook the meat all the way through to the middle. Conversely, with vegetables, the vegetables are simply cooked at an extremely high temperature until they are done. With many vegetables, this will also bring out an inherent sweetness, as the heat will cause complex carbohydrates to break down and become sugars.
Roasting vegetables is the simpler process of the two. Usually, the oven is first preheated to 500 degrees Fahrenheit, and then the vegetables are prepared. Little preparation is really needed; most vegetables can be thrown in as is, although some denser vegetables, such as potatoes, are chopped first to allow for faster cooking. When vegetables are being prepared for roasting, they should be sliced to relatively the same thickness so that they are all done at approximately the same time. Otherwise, the vegetables are drizzled with oil to promote cooking and seasoned with salt and pepper. Different sizes and types of vegetables cook at different rates, so the cooking time can vary greatly. While this process is basically done to cook vegetables, with certain vegetables such as onion, garlic, and peppers, roasting will actually change the flavor of the vegetable and turn it into a completely different food.
Roasting meats is a tad different from roasting a vegetable. First, there is the selection of meats. Only relatively tender (fatty) pieces of meat will work for roasting. Tougher meats will only become more difficult to eat after roasting, and should be braised or stewed instead. If the meat is a long-shaped piece of meat, such as whole tenderloin, it should be approximately the same thickness throughout, so that one end of the meat does not become dry while the other remains uncooked. The meat can be marinated or otherwise seasoned before cooking, although only preparing immediately before cooking will also produce excellent results. Like the vegetables, the meat is usually drizzled with oil and also seasoned. The meat should be aggressively seasoned, since typically the meat will be quite thick and thus need a good bit of seasoning.
In roasting the meat, the meat should not be touching the pan so that it does not end up stewing in its own juices. The meat is usually kept off the bottom of the pan with either a roasting rack or a bed of vegetables placed under the meat that can serve the same purpose. Typically, the meat is then placed in an extremely hot oven (500 F) until it is well seared all around, usually around twenty minutes. Then, the oven temperature is dropped down to about 350 F to allow the meat to cook all the way through. When checking for doneness with a thermometer, the concept of "carryover cooking" should be kept in mind. This term refers to the fact that an extremely hot food will continue cooking to some degree even after it has been removed from all pots, pans, ovens, etc. In other words, to reach the desired cooking temperature, the meat should be removed early and then allowed to rest. This will allow the meat to reach the desired temperature rather than overshoot it and also allow the juices to redistribute themselves. If the meat is sliced immediately after removing it from the oven, the juices will run, thereby drying out the meat. After a rest of fifteen minutes to half an hour, the meat will be ready for serving. The drippings in the pan can also be used to create a sauce for the meat itself.
