Microwaving metal bowls

[equality5271]

When I was at the CIA, a couple the chefs said we could use metal bowls in the microwave as long as the bowl did not touch the sides of the microwave. The microwaves there were not the home use ones..but more heavy duty. Nothing ever caught on fire.

Is this true in all cases? I'm scared to put a metal bowl in my home microwave, but it would help a lot when I am in the kitchen.

Edited February 3, 2008 by equality5271 (log)

[grumpy7]

I have some metal camping dishes that I put in the microwave all the time with no problem. Just a regular household microwave.

[K8memphis]

I can put stainless steel in the microzapper, but not other metals. My understanding is that it has something to do with the water content of the metal.

[Linda Rose]

When I was at the CIA, a couple the chefs said we could use metal bowls in the microwave as long as the bowl did not touch the sides of the microwave. The microwaves there were not the home use ones..but more heavy duty. Nothing ever caught on fire.

Is this true in all cases? I'm scared to put a metal bowl in my home microwave, but it would help a lot when I am in the kitchen.

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Just try it. If it arcs (sparking), assume it is bad and turn it off. It it doesn't arc, then it's good to go.

[DerekW]

You can put metal objects into a domestic microwave, but there are a couple of reasons why you might not want to do so:

Metal reflects microwaves [the inside of the cooking chamber is metal, and that's what keeps the energy in there where you want it. Using a metal container will shield the container's contents from the microwaves to some extent. Might be what you want, might not.

The microwave cooker is designed to avoid reflecting significant amounts of energy back out of the cooking chamber back towards the source [magnetron]. Too much energy being reflected back can damage the magnetron and by placing a reflective metal object in the cooking chamber you run that risk. Bowls, having curved sides, make poor reflectors from most angles.

"Pointy" metal objects can act as handy little jumping off points for concentrations of radio frequency energy, and sparking can occur there. "Pointy" here could be the peaks of crinkles on a piece of foil, or something more obviously pointed like a skewer. Bowls, by their nature don't usually have such forms, but the little specs of metal in ceramic glaze can look pointy to the RF. My guess, without having tried this for confirmation, would be that a metal bowl actually touching the side all the time would not be a problem, but one which was making and breaking contact due to vibration would probably spark, hence the 'no touchy' instruction.

[grumpy7]

It looks like someone tested it out already.

[paulraphael]

It looks like someone tested it out already.

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That's interesting.

Especially because I've had issues with some of my mom's ceramic dishes that have designs done in metallic glazes. They arc like crazy in the microwave, and the glaze actually gets pitted. I've assumed you'd have the same kinds of problems but worse with big pieces of metal.

I'd be curious to see more details of the study, and to know if it was subject to peer review, since it (and an earlier, similar study) was funded by metal packaging manufacturers.

Edited February 4, 2008 by paulraphael (log)

[Chris Hennes]

Especially because I've had issues with some of my mom's ceramic dishes that have designs done in metallic glazes. They arc like crazy in the microwave, and the glaze actually gets pitted. I've assumed you'd have the same kinds of problems but worse with big pieces of metal.

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As DerekW pointed out in his excellent post above, it is not so much metal that is the problem, it is the pointy metal edges. Many microwaves come with metal shelf units, after all! The sharp edges of thin metal foils cause big arcing, as can the tines of a fork, but food packaging can certainly be designed to avoid this. The metal glaze on your mom's dishes is more like aluminum foil, or possibly even worse if the glaze looks more like zillions of tiny metal shards (at the microscopic level, of course). There are other issues related to the metal reflecting some of the microwaves, and I have read claims that this can damage the magnatron, but I personally microwave my metal thermos-style coffee mug on a regular basis with no apparent ill effects.

[devinl]

When I was at the CIA, a couple the chefs said we could use metal bowls in the microwave as long as the bowl did not touch the sides of the microwave. The microwaves there were not the home use ones..but more heavy duty. Nothing ever caught on fire.

Is this true in all cases? I'm scared to put a metal bowl in my home microwave, but it would help a lot when I am in the kitchen.

←

I believe stainless steel can be used in the microwave. But you have to be careful though. I know of someone who microwaved a steel bowl, but the handles was another metal (I can't remember what), that didn't spark in the microwave. Unfortunately for him, the metal handles were super hot and stuck to his hand.