Microwaves are like light waves. Microwaves can pass through some things, are absorbed by some things and reflected by other things. Light can pass through clear glass, is absorbed by dark objects (like black upholstery in a car) and is reflected by light objects (like white upholstery).
When microwaves pass through something, like glass, they do not have an affect on it. When they are reflected, such as by metal, they also have no affect on the object. But when they are absorbed, like light being absorbed by the black upholstery, heat is generated. One difference with microwaves is that they penetrate food and so cooking occurs throughout, whereas light waves do not penetrate and so heat from the outside inward. *Note that glass and metal actually do absorb some microwaves and heat up because the glass and metal we use is neither perfectly transparent nor perfectly reflective. Most of the heat they pick up in the microwave is through heat conducted from the food itself.
The unique thing about microwaves, and what makes them useful for cooking, is that they happen to be absorbed by water, fat and sugars. Most foods are comprised of some combination of water, fats and sugars. So, because foods absorb microwaves, they get hot, much like black upholstery absorbs light and gets hot. Microwaves pass through glass and some types of plastic generating little or no heat.
The Mechanics of a Microwave
Electrical current travels through the controls, a fuse, a thermal cutoff, a safety interlock on the door, to a high-voltage transformer and then on to the magnetron. The magnetron uses very high voltage and for this reason, we do not recommend that you open your oven to make repairs. This voltage remains in a capacitor even when the oven is unplugged. Because of the deadly voltage, the high cost of parts and the low cost of a new oven, replacement is very often a better option than repair.
The magnetron requires the high voltage to generate microwaves. The waves are then focused into the cooking chamber. The interior surfaces, including the mesh over the window, are metal and reflect the microwaves so that they penetrate the food from all sides to heat the food evenly. A stirrer and/or a turntable are used to further improve the even absorption of the microwaves.
Microwave Tips and Advice
- It is better in most cases to cook longer at a lower temperature rather than the other way around.
- To clean food baked onto the interior of the oven, heat a cup of water for about three minutes and then let it sit for another five minutes. The steam will help to loosen the food and make it easier to clean.
- Even after the oven shuts off, the heat in the food allows it to continue to cook. Let food remain in the oven to allow more even distribution of heat in the food, or remove it from the oven immediately to prevent over cooking.
- Point a container away from you when opening.
- If your microwave oven is malfunctioning, try unplugging it for a couple of minutes. When you plug it back in it may reset and resolve the problem.
- Don’t repair your own microwave oven. Even when unplugged the capacitor has a deadly high voltage charge.
- Never heat sealed packages or containers in the microwave unless instructed to do so.
- Puncture food such as whole apples and potatoes so steam can escape.
- Don’t overheat liquids, they can virtually explode out of their container when moved or something is placed into the liquid.
- Use a pot holder when removing anything from the microwave oven.
- Never stand over a hot container when opening.
- While there are cases in which metal can be safely placed inside the microwave, it should be kept well away from any part of the interior. Metal (this includes foil) also interferes with the microwaves even distribution, so the use of metal should be minimized.