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MICROWAVE OVENS The microwave oven is one of the great inventions of the 20th century. It uses microwaves to heat food. Microwaves are radio waves, with the frequency of roughly 2,500 megahertz (2.5 gig hertz). These radio waves have an interesting property: water, fats and sugars absorb them. On absorption they are converted directly into atomic motion - heat. Another interesting property of waves in this frequency is that plastics, glass or ceramics does not absorb them. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven. How Microwave Ovens Cook Food It is often said that microwave ovens cook food "From the inside out." What does that mean? Suppose you bake a cake in a conventional oven and accidentally set the oven at a higher temperature than required. What will happen? Outside of the cake will burn before the inside even gets warm. In a conventional oven, the heat migrates from outside of the food toward the middle. The dry, hot air on the outside of the food evaporates moisture. The outside thus can be crispy and brown while the inside is moist. On the other hand in microwave cooking, the radio waves penetrate the food and excite water and fat molecules evenly throughout the food. The heat does not have to migrate toward the inside. The heat is everywhere all at once because the molecules are all excited together. Of course, there are limits. Microwaves penetrate unevenly if food pieces are thick and do not reach all the way to the middle. The whole heating process is different because you are "exciting atoms" rather than "conducting heat". Inside the microwave oven, the air in the oven is at room temperature, so the crust does not form. |
