How does a Microwave Work?

Microwave ovens revolutionized the way we eat. Cooking incredibly fast compared to conventional ovens, a microwave turns even healthy food into “fast food.” Strangely enough, we can thank radio waves.

A microwave oven generates radio waves in the range of 2.5 gigahertz. This spectrum lies between FM radio waves and infrared rays, the latter of which border on detectable light at the red end of the visible light spectrum. Radio waves in the microwave range have favorable properties in that they are absorbed by food – or liquids, fats and sugars.

When food in a microwave absorbs radio waves, the energy translates into atomic motion, which becomes heat. In other words, microwave radio waves excite the atoms that make up food. This results in evenly and quickly cooked food, all things being equal. In reality, some types of food do not allow equal penetration of radio waves, resulting in “cold spots.” This is a concern with poultry, meat and eggs, where bacteria can survive in the uncooked areas.

To ensure that food cooks evenly in a microwave, some experts recommend covering the food with a vented lid or microwave-approved plastic wrap. With this method, hot steam builds under the lid or wrap, raising the temperature to kill any bacteria and help cook the food more evenly. If cooking a large piece of meat, cooking at 50% power for a longer period of time might yield better results. One can also use a meat thermometer to ensure that food is cooked to the right temperature.

A microwave is probably used more often for reheating leftovers or frozen foods. Unlike a conventional oven that must be preheated, a microwave doesn’t waste energy heating the air inside the oven. Only the food gets heated. Plastic, ceramics and glass also do not absorb microwave radio waves. For this reason, some microwaveable foods come with a reflective “browning sheet” to intensify heat in a specific area in order to brown the bottom of a pizza, for example, or the top of a pastry.

Since a microwave does not heat containers it is easy to assume that food is cooler than it actually is. Be careful not to burn yourself with foods taken from the microwave. Experts warn to be especially careful with baby bottles. The bottle might seem fine to the touch, while the liquid inside could be close to boiling. Heating baby bottles on the stove in a pan of warm water may take a few minutes longer, but it’s safer for your baby in the long run. If you do use a microwave to heat a baby bottle, always test the milk or formula on your wrist before giving it to the baby – a ritual that should be used even when heating the bottle on the stove.

At one time, people worried about the idea of eating food cooked by radiation until it was understood that all heat is radiation. Nevertheless, it’s recommended to stand 20 inches (51 centimeters) or more from a microwave while it’s cooking. If there is a radiation leak, this will minimize exposure. If the door of your microwave ceases to click shut properly, it’s time to have it repaired or replaced. Use a conventional oven in the meantime and avoid operating a microwave that you know to be leaking or faulty.