Microwave Rundown

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Dear Home Ec 101,
How does a microwave work? Also, if you’re not supposed to put metal in a microwave, why do my Hot Pockets™ come with a foil lined sleeve?
Dyspeptic in Des Arc

Heather says:

I have some deliciously geeky friends who will probably rip the explanation I’m going to give you to shreds, but I want them to keep in mind I’m trying to break this down to as simple a concept as possible. I’ve talked about the manner in which heat is transferred before. With conventional ovens, you have indirect heat, the heating element heats up the air which then heats up whatever you’re cooking. Your stove is an example of direct heat, your burner heats up the pan which is in contact with your food. Now please don’t get all weird on me and say, “But Heather, the burner isn’t touching the food, so how can it be direct?” Pans are simply a convenient way to transfer the heat and keep the mess under control.

how a microwave works

So, what about microwave ovens? Microwaves are electromagnetic waves, just like radio waves or visible light, the difference is the length. Your microwave has an antennae that broadcasts these waves inside the appliance.  How come the waves don’t go right through the glass? The waves don’t escape because you don’t need a solid wall to contain them, think about how a tennis court typically has a chain link fence. We can see through it, but the holes in the fence aren’t large enough to let the tennis ball escape. It’s the same principle.

I know a droplet of water is round, but the molecules it contains aren’t. Individual molecules of water are bent, almost like a V. The two hydrogen atoms would be the positive side and the oxygen atom creates the negative. Since opposites attract, this keeps individual water molecules hanging out with one another. The microwaves broadcasted by your appliance excite the water molecules in your food causing them to flip back and forth.  Rub your hands briskly together for a moment and you create heat through friction. Your microwave heats your food by creating friction between water molecules and the molecules they are in contact with. This is why if you heat a glass of water in the microwave the water can boil before the cup gets hot. If you let the water sit in the glass for any extended period of time if would heat through conduction or contact with the hot water. It’s not the microwaves interacting with the glass.

  • Covering food in the microwave helps it heat faster by creating a pocket of steam; it also contains the splatter.
  • Stir food that has been microwaved to ensure there are no hot or cool spots.

Now some of you may be saying, aren’t microwaves dangerous? Why don’t you use yours more?

For me, it’s mostly a texture thing. It’s the same reason I don’t steam a lot of foods. I prefer the magic that happens when food is seared or the crusty perfection of baked goods. When it comes to microwaving, use common sense and don’t use plastic that isn’t designed for the appliance. The plastic may melt partially during cooking and leach chemicals into the food. To play it safe, I try to only microwave in glass or ceramic.

I’m not sure whether to address the issue of metal in a microwave or the fact that you are eating Hot Pockets™ -Whoops, there goes another potential sponsor, right?

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It’s not the metal that causes the problem, but the shape of the metal. -It’s not you, it’s me.-  The problem is arcing, or the build of  a charge that jumps from one point to another. It’s like a miniature thunderstorm in your microwave. Create enough mini-lightning bolts and something will get zapped. Your Hot Pocket™ sleeve is flat, it reflects the microwaves back to the crust of your food and to the fat in the pastry which also gets excited, this creates enough heat to brown your snack.


Send your domestic questions to helpme@home-ec101.com.

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12 thoughts on “Microwave Rundown”

  1. Safety tip: Don't ever put a CD in the microwave and set the timer for just a few seconds and turn it on. Because the really cool lightning show you'll see is going to destroy the CD. And the microwave oven.

    And if you decide you're not going to take my advice and do this stupid thing anyway, then at least do it outside. Unless you want to burn your house down too.

    ~~ThatBobbieGirl, who no longer cooks with a microwave oven

  2. Back in the day, we used to put an open can of frozen juice in the microwave for just about 10 seconds to make it easier to work with. The sides of the can are cardboard and the metal bottom never caused any trouble. although I'm not sure it was a good idea.

    Alton Brown has a microwave popcorn method that uses a paper lunch sack and a couple of staples. You have to make sure the staples are far enough apart so they don't spark, but they otherwise don't cause a problem.

  3. Also, don't put a metal bowl in the microwave to melt chocolate, realize what you just put in, then reach in and grab it out with bare hands. My thumbprint is now permanantly attached to that bowl.

  4. Have you ever seen a water molecule after it has been microwaved? A Japanese scientist wrote a book with lots of photos called "The Properties of Water". I've thrown my microwave away.

    • Jane, i think that all technology has a good and a bad side. Just like most people in Western society enjoy the benefits of a light bulb, artificial light in great concentration causes light pollution, which annoys astronomers and can disturb wildlife.

      My opinion is that if we use technology, such as a microwave oven, responsibly, then the detrimental effects are kept to a minimum.

    • I would imagine a water molecule would look just like a water molecule after being microwaved. The amount of energy in the microwaves used in a microwave oven is definitely not enough to cause water to dissociate and any change to the shape of a water molecule (water is a polar molecule with an angle of 104.5 degrees between the H-O-H), if any, would be temporary. I wouldn't expect that microwaves would have enough energy to change that H-O-H angle.

      Don't suppose you know the author's name on that book? Now I'm kind of intrigued to see what's in the book.

  5. I am glad to know, more specifically, how the microwave works. I, honestly, rarely use it. It is really just used for popcorn and pizza roll snackies at this point in my life. Oh, and the timer is pretty nifty and is loud enough to wake me up from my afternoon siesta!

    I've always thought microwaved food tasted somewhat icky.

  6. Me? What makes you think I did such a foolish thing? I'm shocked!

    I was in my mid-thirties. I blame the internet.

    I'd read about it online a while before, but knew it was a bad idea. So, when we had a microwave we were tossing anyway even though it still ran, because it would KEEP RUNNING WITH THE DOOR OPEN! Had to unplug it to stop it. This was my chance. I grabbed one of the 7,324 free AOL CDs we had gotten in the mail, took everything outside and used an extension cord. I made lightning in the microwave. It was pretty cool, but then, I'm easily amused.

    I have a microwave oven now, only because someone had heard that ours died and gave us another. I do not cook with it.

    So, why have it? Our house gets pretty cold in winter, and use it to heat up bed warmers. Old socks filled with dry beans or rice, to tuck in at our feet in our beds.

  7. That is hysterical! I am willing to try things like that from time to time. I just had to know what triggered the experimentation.
    I love rice socks. I think they have to be, hands down the best use of old socks known to man.


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