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Do we have to wait a few seconds to let the microwaves go away, or can we eat it immediately?

Of course, I assume that the food is not too hot to be eaten.

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3 Answers 3

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Yes it is completely safe. Microwaves do not linger in food. The microwaves stop as soon as your microwave stops.

A microwave is just an electromagnetic wave similar to a radio wave, but at a higher frequency. It works by exciting molecules, particularly water, in the food and giving those molecules some of its energy as heat.

Microwaves do not alter the structure or composition of molecules or atoms directly, which is what happens with ionizing radiation (gamma rays, x-rays, and UV-rays). You could cook your food with gamma rays, but you would ionize many of the particles making them radioactive.

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Wait...so you're saying I shouldn't be using gamma rays to cook my food? –  Michael Mrozek May 17 '11 at 3:36
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UV-rays can knock electrons off, but do not actually alter anything in the nucleus. They will not make food radioactive, but might alter its molecular structure (as can microwaves - burning is altering the chemical structure of the food). But x-rays and gamma rays can actually alter the nucleus of the atom rendering it unstable. This can, potentially, make things radioactive. Don't mind me though, I'm just a pedantic geek who knows more than any sane person about physics. –  Omnifarious May 17 '11 at 6:24
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The only thing you have to be careful of is heating liquids in ceramics. Because ceramics are smooth, they can prevent nucleation points from forming which normally allow the liquid to boil. This means the liquid can superheat, and when you take the bowl out, which sloshes the liquid around and creates nucleation points, it can explosively phase-shift into steam. But that's a worst-case scenario :) –  ElendilTheTall May 17 '11 at 7:45
    
@ElendilTheTall: I've actually had that happen to me, though luckily it happened in the microwave. I was heating a mug full of water and trying to get it to boil. It was taking a long time. Then, suddenly, I hear a muffled "WHUMP!" from the microwave. I turn it off. My mug is now 3/4 empty and there's water all over the inside of the microwave. –  Omnifarious May 17 '11 at 13:04
    
Yup. It often happens if you boil water in the microwave and then put a tea bag in - tea-bag = nucleation points = whump! –  ElendilTheTall May 17 '11 at 13:20

I'm assuming you're thinking you might have to wait for the microwaves to disappear from the food? (Edit: actually, you said so explicitly …) Well, I don't think the physical properties of microwaves work that way. ;) Interestingly, here's an article titled “Microwaved Food Isn't Safe to Eat”, which I'm personally taking with a large grain of salt; but note that of all the claimed dangers with microwaved food, the possibility of “ingesting” microwaves isn't one of them! (The article does claim health problems have arisen from the microwave field next to a microwave oven; which is contradicted by the information found on Wikipedia.)

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That's one hell of an article. Here's my favorite quote: "Microwaves destroy the life-force that gives food its vitality and nourishment." –  Gabe May 18 '11 at 4:12

Regarding the microwaves going away: Microwaves are essentially the same kind of electromagnetic radiation as light, just in a different frequency range. If the oven's light-bulb gets turned off at the same time as the magnetron, the microwaves should be gone by the time you stop seeing the light.

Regarding safety: I have eaten microwaved food on several occasions with no ill consequence. Of course, there may be long term effects I'm not aware of but you might try asking about that on a biology-oriented site since hobodave has already ruled out radioactivity from the physics perspective.

I am not a biologist, micro- or otherwise. I'm also not a nutritionist, but I've heard that microwaves can reduce the nutritional value of food. I'm certainly willing to believe that the interactions are small and complicated enough to be very difficult to fully observe. Further, I can believe that the pro-microwave and anti-microwave lobbies are pretty lop-sided in terms of funding and effort. Finally, it seems to me that nutrition is a complex enough subject for a lot of nutritional advice to be under constant revision.

Given those thoughts, I see the following possible approaches:

  1. Eat a ratio of microwaved to non-microwaved food commensurate to your risk tolerance/aversion (cost) vs. perceived convenience, etc. (benefit).
  2. Accept a credible, seemingly balanced viewpoint such as this one: http://www.health.harvard.edu/fhg/updates/Microwave-cooking-and-nutrition.shtml
  3. Fund/oversee one's own clinical study over a number of years, applying one of the prior options while you await the results.
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