You should not put aluminum foil in a microwave oven.
More Info: All microwaves are not created equal. Some are smaller, some have rotating plates, and others can actually handle small pieces of aluminum. It all depends on the type of microwave that you own. However, there is also the chance that the aluminum foil or any metal object for that matter inside of a microwave will catch fire. To understand why, you have to understand the way that microwaves work.
How Microwaves Work
As the name implies, microwaves heat food through microwave radiation. Rather than a heating element like the heating coil in an oven, a microwave has a magnetron, which converts the energy from an electrical outlet into microwaves. These microwaves then pass through a waveguide that controls the direction of these electromagnetic waves and sends them into the cooking chamber. Food absorbs these waves, exciting the molecules, which creates heat thus cooking the food. Metal, on the other hand, reflects these waves creating surface electrical currents. Corners and bends in the metal can concentrate the fields even more causing extreme heat, sparks, and possible fire.
Why Some Microwaves Handle Aluminum Better Than Others
The owner’s manual can tell you a lot about what your microwave can and can’t handle. Newer microwaves have fewer restrictions on metal and aluminum objects. Still, it’s a little questionable to place such objects into a microwave. Any object covered in aluminum foil or placed in a metal tin should not be placed in a microwave oven. That’s because metal prevents microwaves from being absorbed by the food. The aluminum foil will actually cause damage to the microwave oven if there is too much covering the food.
Using Aluminum Foil to Shield Food
In some cases, little bits of aluminum foil can protect or prevent microwaves from heating up that area, such as when cooking chicken wings or drumsticks. This helps to not overcook the meat. There are also certain types of foil containers that are microwave-safe. For instance, aluminum foil is often used in certain frozen entrees on the bottom of the tray to keep the food heated thoroughly.
Being Safe with Metal, Aluminum and Microwaves
There are some rules to follow with properly using microwaves and aluminum foil. For one, only use new, smooth foil. Wrinkled foil actually produces more sparks inside the microwave. No more than a small portion of the food should be covered with aluminum foil. In addition, when placing food and containers that have small portions of aluminum foil, make sure these are placed inside the oven in the center and not near the walls of the chamber. Monitor food closely to see if there are any sparks from the foil. Remove the foil completely if you notice too many sparks, as it could be a fire risk.
Journal of Physics Education; Michael Vollmer
Physics of the Microwave Oven
UCSB Science Line
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Cornell Center for Material Research
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