Cooking bags are designed for use in conventional ovens because they are much larger than countertop roaster ovens, and can more easily accommodate the bags. Some bag makers, such as Reynolds, recommend never using them in roaster ovens because the bag can melt during the cooking process. However, if used with care and planning, cooking bags can work in some roasting ovens, as long as the oven is not too small.
Measure the interior dimensions of the roasting oven, wall-to-wall and from the rack to the top or the upper elements (place the rack on the lowest setting). Compare to the dimensions of the partially inflated cooking bag. It is essential that no part of the bag touches the top, sides or door of the oven during cooking. Remember that the heated air trapped in the bag will expand, partially filling the bag. Do not use the bag if the oven is too small. You should be aware of the moisture content of the food cooking in the bag because the longer the food cooks, the more the bag will expand. For instance, many vegetables contain more water than meats.
Open the top of the cooking bag and add a tablespoon of flour. Twist the top of the bag to temporarily seal it, and then shake the bag to distribute the flour. The flour layer will prevent food from sticking to the bag.
Shake out any residual flour from the bag.
Place the food in the bag and seal the bag with the fastener provided with the bags; do not fill the bag with air. Center the food in the bag with two inches of room on all sides. If more than two inches of bag extends beyond the fastener, cut off the excess with scissors.
Place the food-filled bag in the center of a cooking dish, roasting pan, etc. Center the pan or dish in the oven.
Watch the food while it cooks, especially as the bag expands. If the bag touches any interior surface of the roaster oven during cooking, remove the food from the oven and use a conventional oven.