Microwave ovens cook by heating water and chemical molecules in food with short-wave radio energy, similar to that used in radar and television. The frequency most commonly used in the microwave oven is 2,450 megahertz.
One of the microwave oven's advantages is it provides the quickest possible means of de-frosting, heating, and cooking. Microwave ovens consume the least amount of energy and are highly space efficient. The ability of microwaves to defrost and warm foods in a matter of seconds makes these units popular with food service operators wanting to offer high menu variety to a large volume of customers. These establishments often pre-cook foods and refrigerate them until peak serving periods and then quickly heat these portions during peak time periods.
One disadvantage of the microwave, however, is that because it cooks foods from the inside out, as opposed to outside in as with most systems, it may not provide the surface browning effect desired in many cooking applications. This can be solved by transferring the food to another type of oven for this final step.
Cooking capabilities differ only minimally among different microwave oven models. Microwave ovens are available in an array of sizes and with a number of features. Top and bottom, or bottom-only energy feeding systems are available. Each type has rotating wave guides to minimize "hot spots" common to residential style units.