Can You Put Metal in the Microwave?
No, you should not put metal in the microwave in most cases. Metal reflects microwaves and can cause sparking, fires, and damage to your microwave. This includes utensils, aluminum foil, twist ties, and containers with metallic trim. Some microwaves have specific metal accessories designed for use with them.
Key Takeaways
- Microwaves heat food by emitting electromagnetic waves that cause water molecules to vibrate.
- Some modern microwaves include metal racks or crisper plates designed to be safe in that specific unit.
- Metal-rimmed dishes and plates with metallic decorations should never be microwaved.
Explanation
Microwaves heat food by emitting electromagnetic waves that cause water molecules to vibrate. Metal reflects these waves instead of absorbing them, causing the energy to bounce around inside the microwave and potentially arc between metal edges.
When microwaves arc, you see sparks that look like tiny lightning bolts. This can damage the microwave's magnetron (the component that produces microwaves), burn holes in the interior, or start a fire if sparks ignite nearby food or paper.
The shape of metal matters significantly. Sharp edges and thin metals (like twist ties and foil) are most dangerous because they concentrate electrical charge. Smooth, thick metal with no sharp edges is less likely to spark but still not recommended.
The physics behind metal arcing involves the buildup of electrical charge at thin edges and points. Microwave radiation at 2.45 GHz induces currents in metal surfaces, and these currents concentrate at sharp points, thin edges, and where two pieces of metal are close together. The voltage can exceed the breakdown voltage of air (roughly 30,000 volts per centimeter), creating a visible spark. A fork's tines are spaced close enough to arc between them, while a spoon's smooth, rounded surface may not spark at all—though using one is still not advised.
The magnetron tube that generates microwaves costs $50-150 to replace and can be permanently damaged by reflected microwave energy. When too much energy bounces back from metal objects, it can overheat the magnetron's cathode filament or crack its ceramic insulators. Even if no visible damage occurs, repeated metal incidents can shorten a microwave's lifespan from the typical 10 years down to just a few.
Things to Know
- Some modern microwaves include metal racks or crisper plates designed to be safe in that specific unit.
- Metal-rimmed dishes and plates with metallic decorations should never be microwaved.
- If you accidentally run the microwave with metal and nothing happens, stop it immediately and consider yourself lucky.
- Small pieces of aluminum foil can be used in some microwaves to shield parts of food from overcooking, but only when the foil is smooth, flat, and covers less than one-quarter of the food surface—consult your microwave's manual first.