It is a bad idea to use aluminum foil in the microwave. You can cause arcing and sparks inside the microwave that can damage your unit, shortening its useful life or even ruining it. It’s also possible to start a fire inside the microwave by using aluminum foil. However, it is technically possible to use foil inside your microwave oven, as long as you follow certain precise steps. When used correctly, foil can be helpful in the microwave because whatever it covers will not be heated, as the microwave radiation cannot penetrate the metal. Thus, aluminum foil can shield certain portions of a food from being heated. For example, according to GE, foil can be used to cover the leg tips or wing tips of a turkey or the ends of a leg of lamb. If you choose to use foil in your microwave, do so with extreme caution by following the steps below.
The main thing you want to avoid when using aluminum foil in the microwave oven is sharp edges, wrinkles, crumples, or any portion of the foil sticking up like a flag. Edges or loose pieces act like antennas and can cause electrical arcing that can impact the walls of the microwave and feed back into the magnetron. This will damage the magnetron or even cause it to stop working.
General Guidelines for Using Foil in the Microwave
- If you wrap food with foil before microwaving, it should be tightly wrapped around the food, and no pieces of foil should be sticking up.
- Do not try to heat food entirely wrapped in aluminum foil, as the foil will reflect the energy.
- If you use foil to put food on or to cover food to prevent splatters, the foil should lay flat and smooth and the edges of the foil should be at least one inch from the wall of the oven.
- Do not use metal utensils inside the microwave, and do not let foil make contact with other metal inside the microwave, including the metal rack that may have been provided for your unit.
- If using foil in the microwave, use the turntable, not the metal rack.
As stated above, it’s not a good idea to use aluminum foil in the microwave, and if you do use it, you do so at your own risk. The owner’s manual for your microwave oven may have specific guidelines for using aluminum foil. You should follow these guidelines.
Why Does Aluminum Foil or Other Metal Cause Sparks in the Microwave?
You may have seen the light show in a microwave when you place a metal object or crinkled aluminum foil inside. The foil packages of Pop-Tarts are notorious for doing this when people mistakenly put the still-wrapped tart in the oven. The resulting orange light and bright blue sparks can be dramatic. Sometimes, you will even see what looks like actual fire as the aluminum foil is heated to an extremely high temperature. Caroline A. Ross, Toyota Professor of Materials Science and Engineering, explains what is happening, via MIT School of Engineering.
The oscillation of the microwaves can produce a concentrated electric field at corners or an edge of a metallic object, ionizing the surrounding air “so you can hear it popping away,” says Ross. You might also see sparking, which “is a little like lightning,” she adds. This kind of microwave sound and light show isn’t limited to metal. Ross sometimes puts on a demonstration for her kids: She cuts up hot dogs, creating sharp edges, and “watches the electric sparks jumping between them.”
It’s true! Even food can spark in the microwave. Green beans are known to cause sparks when microwaved, due to their high mineral content. Carrots, kale, peppers, and the aforementioned hot dogs can also cause electrical sparking in the microwave. Even grapes have been known to do this, although I don’t know why anyone is heating grapes in the microwave. These foods are rich in minerals like iron, magnesium, and selenium, but let’s not be confused. Minerals in foods are like tiny pieces of metal. Therefore, if there are enough of them, they can cause electrical sparks.
