Microwave oven

A microwave oven is an oven that heats food with microwaves (a specific wavelength of radio waves). This has led to a certain amount of concern among people who don't know how stuff works.

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Claims

Microwave ovens aren't natural!

Neither are using computers, living in buildings or wearing clothes. If you want to live in a cave naked, go ahead.

The Nazis discovered microwaves![1]

Radio waves were indeed first discovered in experiments by German physicist Heinrich Hertz, based upon James Clerk Maxwell's electromagnetic theory of light. But Hertz died decades before the Nazis came to power and worse yet, after they did, tributes to Hertz for his scientific discovery were purged from public view because of his Jewish heritage.

Claims about the Nazis inventing microwave ovens are contradictory and without evidence. Some claims purport that large microwave ovens called "Radiomissor" had been used by the Wehrmacht during Operation Barbarossa, the German invasion of Russia in 1941. Which of course conveniently ignores the fact that Russia's electricity grid at that time was very sparse, and the Wehrmacht due to its rapid advances already faced great difficulty supplying tanks with fuel, so running electricity generators for the sake of powering microwave ovens seems rather impractical, when horse-drawn field kitchens were widely available and the acquisition of firewood trivial.[2]

In contradiction, other claims state the microwave oven was researched by Nazi scientists for the use outlined above, but cancelled because it was allegedly found that microwave oven food caused cancer (see points below). This again ignores the historical fact that the far more useful military application of microwaves lay in radar, which was still new technology at the outset of World War Two and it therefore would have been unreasonable to direct such research to the purpose of food preparation. It was in fact Percy Spencer, a leading researcher of American radar technology, who would invent the microwave oven shortly after the war and its development by the Raytheon company is well documented. [3]

Last but not least, if there were a moral imperative that we shouldn't use things the Nazis invented, we would also have to stop driving cars on highways, flying around in jet planes, depending on satellites shot into space with rockets, etc.

Did James Lovelock really invent the microwave oven?

Dr. Lovelock does claim this on his website and certainly did it before it was commercial and widely available. However the microwave oven was patented in 1945; the earliest claim Dr. Lovelock made was in a 1955 journal article on the reanimation of cryonic preserved rats using microwave diathermy. [4]

Why did the Soviet Union ban microwave ovens in 1976?

This is a widely purported myth[5], but there is no evidence it ever happened. The ban was supposedly based on Soviet research linking cancer growth to food cooked in microwave ovens, but no trace of any such research exists either. [6]

Maybe the study was conducted in the city of Chernobyl in 1986.(Warning: Poe's Law in action!)

Microwave ovens destroy nutrients in food![7]

Heat of any kind can destroy a few vitamins and other nutrients in food. Boiling in water can also remove nutrients, because the nutrients migrate out of the food and into the water, which is thrown away. Since microwave cooking usually involves shorter cooking times and less boiling than conventional cooking methods, it actually destroys fewer nutrients than conventional cooking overall. This doesn't mean either cooking method is "bad for you," though -- you probably get enough essential nutrients from other sources anyway, without having to drag raw foodism into it.

Microwaving creates toxins and carcinogens in food![8]

No more so than heating food in a conventional oven does. Yes, a few of the trace compounds created in baking are carcinogenic when ingested in sufficient quantities. But the quantities of carcinogens created by heating food -- in a microwave or otherwise -- are well, well below the threshold where they can have any impact on your chance of getting cancer. Unless you heat it so much that it turns into a lump of charcoal, in which case you'll want to spit it out the moment you taste it anyway. On the contrary, microwaves don't sear the surface and leave burnt bits, which contain carcinogens, so microwaved food is not more but less carcinogenic than oven-baked or grilled food.

Nearly all chemical transformations in microwaved food occur because the food simply gets hot. Just like it does in a conventional oven.[9]

Microwave ovens produce radiation![10]

This is absolutely true. So do light bulbs, ordinary ovens, wood-burning fireplaces, and even human beings. The microwaves generated inside a microwave oven are radio waves with wavelengths from a millimetre to a metre, which carry far less energy per photon than even ordinary visible light. (Gamma rays, by contrast, have wavelengths down to 10-12m, short enough to cause tissue damage by ionization.) The reason microwave ovens are enclosed in wire mesh Faraday cages is because of the amount of microwave radiation, not anything inherently more dangerous about microwaves vs. any other kind of radiation.[11]

Radiation leakage was a concern at one point, but the only way for a microwave oven to leak radiation is if there's a hole in its Faraday cage. And even if there is a hole in the microwave oven, the leaked radiation won't get very far -- within a foot or two, it will have spread out so thin that it won't be any more harmful than the radiation from a cell phone. (Cell phone phobia is another matter entirely....) A hole is bad, but only for the exact same reason you shouldn't leave a conventional oven door open: it's a waste of energy and you could get burnt.

There is one kind of radiation microwave ovens freely emit into the environment: thermal infrared radiation. This is because they are at room temperature, and all objects at room temperature emit thermal infrared radiation. (Scary note: Your microwave oven emits thermal infrared even when it's unplugged!)

Microwave ovens make food radioactive![10]

No, they don't.

Although many people refer to microwave cooking as "nuking" a piece of food, no nuclear processes are involved or induced. About the only way to make a non-radioactive item radioactive is to bombard it with slow neutrons. While nuclear reactor cores do emit neutrons, microwave ovens most emphatically do not.

Microwave ovens cook from the inside out.

Not exactly. The microwave field penetrates a certain distance into food and no further; in meats this is about two inches/5cm. Further cooking is done by heat generated from microwaving the outer parts of the food migrating inward.[12]

They use microwaves at water's resonant frequency

This claim is repeated by a lot of folks, including some physics professors who should know better, and this "fact" usually finds its way to textbooks.

The claim is that microwave heating penetrates into the food, rather than just heating the outside surface, because the microwaves used by these ovens are tuned to exactly the resonant frequency of water molecules. Therefore their energy is absorbed by the water in the food, and bypasses everything else.

Microwave ovens are not tuned to a specific "magic" frequency. Household microwaves produce radiation at 2.45 GHz. Absorption of microwave radiation by water takes place in a continuum of frequencies, with frequencies from 200 to 2.45 GHz being absorbed as much or more than at 2.45 GHz. The maximum is strongly temperature-dependent.[13] The frequency of 2.45 GHz is chosen mainly to avoid interference with radio communications, but other frequencies can be used as well, and large industrial and commercial ovens operate at 915 MHz instead.

Microwaves are able to penetrate to a depth of 1-3 cm into the food. If 2.45 GHz was the exact resonant frequency of water, the water on the surface of the food would absorb all the energy. This would be called - in less technical terms - "grilling".[12]

It is true, though, that wet food absorbs the microwave energy faster than dry food, due to the fact that microwave radiation preferentially excites polar molecules such as water. Each material has its own loss function. Ice is largely transparent to 2.45 GHz microwaves, so that melting frozen foods in a microwave risks thermal runaway - the sides melt and heat to boiling point, while the center stays frozen solid. Ceramics such as ceramic plates and some types of plastics can be heated by microwaves without water being involved. To avoid uneven heating or to speed up heating, you could try to spread water on your food and place a microwave cover on top to retain the moisture -- the microwave will dry your food anyways, so that will get offset as well.

Microwaved water is bad for plants

This claim pops up from time to time: Water that's been boiled in a microwave, and then cooled, is somehow worse for your plants than water that hasn't been microwaved, or water that was boiled on a conventional stove.

Mythbusters did a segment about this, with 4 groups of plants: Plants given straight tap water, plants given tap water boiled in a microwave and cooled, plants given tap water boiled on the stove and cooled, and plants given no water. The result: All plants grew about equally well, except for the plants which were given no water, which all died.

Hitler water!

Masaru Emoto claimed that water that had been microwaved and then frozen would produce ice crystals of a different shape than water that had not been microwaved before it was frozen. He claimed these crystals were just as malformed as the ones produced by yelling "Hitler!" (or projecting other negative thoughts) at the water before freezing it. Food Babe used this "fact" in an article titled "Why you should throw out your microwave," which mysteriously vanished from her website right before her first book was published.

So far as has been determined by rigorous controlled testing, there is no established link between microwave-heated water and membership in the Nazi party.

You can't brown a cake or pie in them

Actually, this one's true :( unless you buy a browning plate which can be heated up to do the browning.

gollark: (Well, I suggested WASM, but this is a stack machine)
gollark: I suggested this ages ago.
gollark: The API doesn't have to do that.
gollark: Solution: Rust, borrow checker.
gollark: Because having no limits would be bad?

References
  1. "Microwave Ovens: The Curse of Convenience"
  2. Microwaves, Nazis, Cults, John F Kennedy, Anti-Semites and Christian Fundamentalists — Or cooking a dinner in 3 minutes flat
  3. http://www.smecc.org/microwave_oven.htm
  4. Andjus, R.K. and Lovelock, J.E. 1955. Reanimation of rats from body temperatures between 0 and 1 C by microwave diathermy. J. Physiol
  5. For example: Why Did the Russians Ban an Appliance Found in 90% of American Homes?
  6. Microwave Myths (pdf)
  7. The Claim: Microwave Ovens Kill Nutrients in Food, New York Times, 17-Oct-2006
  8. The Hidden Hazards of Microwave Cooking, at health-science.com
  9. Kappe et al., Microwave Effects in Organic Synthesis-Myth or Reality?, Angewandte Chemie, vol. 52 no. 4 (21-Jan-2013), pp. 1088-1094.
  10. Radiation, irradiation and our food supply
  11. A 2.45 GHz wave carries 1.0132×10-5 electronvolts of energy. For comparison, visible light is roughly between 1.65 and 3.26 eV, or between 163000 and 322000 times more energetic.
  12. Do microwave ovens cook from the inside out?, on The Straight Dope, 4-Sept-2003
  13. http://www1.lsbu.ac.uk/water/microwave_water.html/
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