How Microwave Ovens Work

The way that a microwave oven cooks food is a mystery to a lot of people. In fact, it is a mystery to some appliance service technicians. Since this website is designed for the do-it-yourselfer, our purpose here is to give a basic understanding of how microwave ovens cook food. In this section we will cover how microwaves cook and a couple of myths about microwave ovens.

Friction

Microwave ovens cook by friction. Assuming you are wearing long pants, take the palm of your hand and move it back and forth on the part of your pants that covers your thighs, you will notice that the palm of your hand will start to get warm. The faster and more aggressively you move the palm of your hand back and forth on your pants, the hotter the palm of your hand gets. Special note: to avoid dirty looks from coworkers, if you are at work reading this while sitting at your desk, you might want to wait until you get home to try this. If you move the palm of your hand on your pants fast enough and long enough, you could produce enough friction and heat to burn your hand. A microwave oven produces a radio wave that cooks by causing the molecules in food to vibrate back and forth very quickly causing friction. A microwave oven has the ability to vibrate the molecules in food back and forth causing friction at a speed of 2450 million times per second, 2450 megahertz (2450 MHz).

Microwave Ovens Do Not Cook Food From The Inside Out

Microwaves cook from the inside out. This is something that you hear all the time, a microwave oven cooks food from the inside out. Sometimes the people that say this don't realize that when they take food out of a microwave oven, it is hot on the outside and still cold on the inside. If microwave ovens cook food from the inside out, then the food would be hot on the inside and cold on the outside. The fact is that the microwave oven electromagnetic wave can only penetrate about 1 to 1 1/2 inches into food. Any food that cooks beyond 1 1/2 inches, is cooking by conducting the heat from the outside in. This is why if you tried to cook a strip of chicken in a microwave oven, it would be dry and rubberlike on the outside, and completely uncooked on the inside. This myth probably started by the fact that microwave ovens cook by vibrating the molecules on the inside of food. Cooking a hamburger on a grill for example, cooks food from the outside and the heat is conducted through the meat to the inside.

You Can Put Some Metal In A Microwave Oven

While it is true that you can not put aluminum foil or other thin type metals in microwave ovens, the inside of a microwave oven is metal! If you have leftover Chinese, that is in a shallow metal container and you want to heat it up in the microwave oven, you can put it in the microwave as long as you make sure it is in the center, and that there is sufficient food in the container to absorb the microwave energy. If you put metal in a microwave and it gets too close to the oven cavity walls, it will spark because the electromagnetic energy is being reflected by the metal. The floor of a microwave oven cavity is shaped in such a way as to help reflect the microwave energy into the food. Using a metal container means that the food can only be heated from the top. So although occasionally you can put metal in a microwave oven, it is not an ideal cooking or reheating situation.

How Does Popcorn Pop in a Microwave

One of the very first things ever cooked in a microwave was popcorn. To be historically accurate, popcorn was actually the second thing. The very first thing ever heated up by microwave energy, was an employee at the Raytheon corporation and a candy bar in his pocket in 1945. If you examine a popcorn kernel closely you will notice that it is completely sealed with a hard outer layer. Inside this protective outer shell is the corn itself and moisture. When popcorn kernels are placed in a microwave oven, the microwave energy starts the molecules in the moisture located inside the popcorn kernel to vibrate rapidly causing friction. The friction is so intense, that the moisture inside the kernel changes from a liquid to a gas. In other words it gets turned into steam. This steam creates such intense pressure, that the outer kernel of the popcorn explodes. That is the popping sound you hear when popcorn is popping. The reason that there are always popcorn kernels left over, is because some of the kernels will have cracks in the outer shell. When this happens the moisture in the shell dries up, leaving nothing behind to turn to steam. Leaving the microwave oven on longer, in an effort to try to pop these left over kernels simply won't work. In fact doing so will diminish the quality of the popcorn that is already popped. Some microwave ovens have a popcorn sensor. The popcorn sensor on a microwave oven is designed to sense the steam that is coming out of the kernels. When there is no longer any steam left in the microwave oven cavity, the sensor turns off the microwave oven and beeps to let you know it's time to eat popcorn. Using the popcorn sensor on a microwave will actually increase the life of the microwave oven. That's because the sensor will only let the microwave operate the oven long enough to cook all the popcorn kernels that still have moisture in them. When a microwave oven operates with little or no load in the oven cavity, that microwave energy is reflected back toward the magnetron. When this happens, the magnetron will deteriorate and fail prematurely.