An oven cooking bag is a transparent, heat-tempered plastic bag made to hold various foods — usually meats and vegetables. These cooking bags are designed not to melt in high oven heat and a moist cooking environment is formed within the bag. They also allow for more even cooking and often faster cooking than using the conventional roasting pan method.
Usually, a little flour is placed in the oven cooking bag and a little shake will help distribute the coating around the bag. Next, the food to be cooked is placed inside and the bag is closed with the nylon twist tie that comes with it. The bag is placed inside a roasting pan or baking dish. Slits in the top of the bag are an important feature because they let the steam escape. The oven racks should be spaced far enough apart so that, when the oven cooking bag expands during cooking, the bag doesn't touch the heating element.
When the food inside the oven cooking bag is cooked, the top of the bag must be slit open carefully to avoid burns from the steam. The food should cool a bit and then be taken carefully from the bag. Directions for each particular brand should always be followed.
There are different varieties of oven cooking bags, such as those for microwave and slow cookers as well as conventional ovens. Using one for cooking a roast can be more convenient that just placing the meat in a roasting pan alone. In the roasting pan only method, the roast will tend to dry out on the top, so frequent basting is required. The cook has to periodically take the pan out of the oven and spoon the juices from the pan over the top of the roast to keep it from becoming dry. An oven cooking bag eliminates the need for this basting because the steam created within the bag keeps the meat moist.