The Big List
Some Microwave Oven Myths
Q: Do Microwave Ovens cook from the inside out?
A: Nope. Food is partially transparent to the radio waves,
so the energy is able to shine through it. But at the same time the
waves are partly absorbed by the food. Usually most of the heat is
produced in an
outer layer about an inch thick. So, large pieces of meat will be quickly
cooked to a depth of about an inch, while the inside portions are cooked
by heat conduction, just like in a conventional oven. This effect is
different for different foods of course. If a food is mostly water, then
the outside inch cooks at all. If a food contains both air and water
(like bread, cake, etc.,) then the radio energy penetrates all the way
through, and the food gets heated everywhere, even deep inside.
Q: If I put a fork in the Microwave, will it destroy the oven?
A: Nope, this is a myth, but it has some roots in reality.
Q: What about the dangerous radiation?!!
In order to safely use metals inside a microwave oven, the cook has to
learn numerous complex and mysterious rules in order to avoid fires and
undercooked food. For example, thin metal will heat up fast in the oven,
and may cause fires. The famous problem of the staple in the paper
popcorn bag comes to mind, where the staple heats up and sets fire to the
And if a metal object in the oven is lightly touched to another one, or
touched to the metal wall of the oven, an electric arc might ignite at the
contact point. If not stopped it can set fire to the oven. Also, sharp
metal edges can cause problems. In the higher
power ovens (800W and above) when the amount of food is small, sharp points
and sharp edges on
metal objects can initiate a corona discharge, a "Saint Elmo's Fire,"
which behaves the same as a flame and can set fire to the food and the
oven if allowed to continue for long. Aluminum foil can become a blow
So, it's much easier to totally ban the use of metals
in microwave ovens. The alternative would be to send everyone to school
to learn the complicated rules!
A: Microwave ovens don't use "radiation." Instead they use
Q: Aren't these ovens tuned to a special frequency so
they only heat water?
Usually when we talk about radiation we mean
radioactivity or "Ionizing Radiation," gamma rays and high energy
subatomic particles. Microwaves aren't high energy, the microwave photons
less energetic than visible light. Yes, if the source of microwaves is a
very "bright" source, it can cook food. If normal light is very bright,
light can also cook food (think of those solar ovens used by
Note that technicians and scientists talk about "microwave radiation" in
the same way that they talk about "optical radiation." Optical radiation
is just another word for VISIBLE LIGHT. They're using the word
"radiation" to mean "waves." In this sense light is radiation, the warmth
of an electric heater is radiation, even radio waves are radiation. And
when you speak, some "acoustic radiation" comes out of your mouth. But
radioactivity is an entirely different thing. Microwave radiation doesn't
sterilize your reproductive organs like high-energy X-rays would. (An
oven with a damaged door can only cook you!)
Speaking of that, how can you tell if your microwave oven is safe?
There's one simple way to detect a major microwave leak. Get a
fluorescent tube and hold it against the edges of the oven's door when the
oven is on. Microwave leakage will make the bulb glow. (Do this in a
darkened room so you'll see the slightest glow.) This works much better
if there is nothing at all inside the oven. If you own an older oven
(pre-1980s) you might want to include a glass of water. However, this method
only shows the larger leaks. Your oven might be leaking too little, so it
won't light a fluorescent tube. To catch even the smallest leakage, you
need a "microwave leakage detector." Search the web for these. I've
sometimes seen them on eBay for $10.
If you have a Microwave Leakage Detector, hold it near an operating
cellphone to get an idea of the accepted level of microwave wattage. Just
like ovens, cellphones use microwaves in the GHz
frequency range. If your microwave oven is leaking far less than your
cellphone antenna, then you need not worry about your microwave oven.
A: No. The usual operating frequency of a microwave oven is
far below the resonant frequency of water vapor... and liquid water
doesn't have a resonant frequency. The peak is 10GHz to 50GHz depending
on temperature, while microwave ovens run at 2.4GHz or 0.9GHz.
Also, the radio energy in a microwave
oven can heat many other substances besides H2O. Water isn't special.
For example, drops of grease on a plastic microwave dish will be heated
far hotter than 100C, and this causes the mysterious scarring which
frequently occurs on plastic utensils. Any molecule which is "polar" and
has positive and negative ends will be rotated back and forth to align
with the changing e-field of the radio waves in the oven. The vibrating
electric field of the radio waves vibrates the oil and water molecules and
any other polar molecules within the food. Jostling molecules equals
heat! Microwave ovens have difficulty melting ice, presumably because the
water molecules are bound together and cannot as easily be rotated by the
If liquid water had a narrow resonant frequency, and if
the oven was tuned to this frequency,
then the water would be far more opaque to the wave energy. The water
in just the food's thin surface would absorb all the energy, and
only the outside surface of foods would be heated. The end result might
resemble the browning and slow cooking of a normal electric oven. Or
perhaps the thin outer surface
of meat would become a blast of steam, and the inside would remain ice
cold. But because water
does not resonate with the microwave frequency,
the waves can travel an inch or so into the meat before being absorbed.
Microwave ovens heat a thick layer of meat, not a thin surface layer.
Another note: single H2O molecules have a sharp resonant
frequency, but liquid water does not. In order to have a distinct
resonance, a water molecule must be alone in space, not bound to billions
identical neigbors. The bonding to neighboring water molecules spoils the
sharp resonance and greatly widens the frequency band. Liquid water has a
absorption band, not a single resonant frequency. In other words, water
absorbs all short radio waves. Typical microwave ovens don't even use the
best frequency. They should be up around 10GHz frequency rather than
the usual 2GHz, but that would make the microwave tube more expensive.
Here's an article about it:
Q: Don't you need distilled water to cause superheating and
"explosions?" Impure tap water only boils, it won't explode.
Of course impure water can "explode." That's why people get
scalded; they re-heat their coffee in microwave ovens and then quickly
sugar. Coffee is extremely impure water! To cause "coffee explosions,"
you don't need special pure water. All you need is water that lacks
It seems that some recent TV show tries to prove that only pure water can
superheat and "explode." This is wrong. Probably the creators of that
show did not know an important fact: nucleation centers for boiling are
actually tiny bubbles. While solid crystals will grow upon solid
nucleation centers found in impure liquids, the gas bubbles in cola, and
in boiling pots, grow upon microscopic seed-bubbles. You can't grow
crystals unless you have a solid microscopic seed. And you can't boil
water unless you have invisibly small seed-bubbles present. It doesn't
matter how filthy your water is, or how many crystal nucleation centers it
contains... if it lacks seed-bubbles then it will not boil normally,
instead it will superheat.
Clearly this has nothing to do with distilled water. In fact it's very
easy to boil ultra-pure distilled water normally, without explosions.
and shake up your bottle of distilled water thoroughly. This creates lots
of nucleation centers for boiling. And it's easy to
make "impure" water explode; impure water called coffee and soup. If tap
water has had all the bubbles cleared
out by earlier boiling or by simply sitting for days in an open container,
then it will superheat, and when sugar is dumped in, it will go DOOSH and
spray all over.
Q: Why do Spagetti-O's explode all over the inside of the oven? BOOMPH!
Heh. I finally figured this out. Took me years. It's the same as with
explosions. If a liquid doesn't have any microscopic seed bubbles,
then it will superheat and explode. There are several common liquids that
totally lack seed bubbles: canned goods, eggs, meat, and vegetables.
Canned goods are boiled and then sealed. The boiling will remove all the
dissolved gases, and as the food cools, the live steam condenses back into
water, creating a fairly good vacuum. That's why the lid on the jar of
spagetti sauce goes "poink" when you break the seal. In a vacuum... THERE
ARE NO SEED BUBBLES. Duh! So Spagetti-Os and jars of applesauce are just
like the explosive coffee which has been boiled and cooled several times.
They're like bombs waiting to go off. There's a possible cure: stir them
first. Stir them well, whisk them up so there's lots of little bubbles
mixed in. (I don't know how well this works, I've only just started
experimenting.) The only other cure is to stick a bunch of wooden
chopsticks into the food. You need several, since unlike coffee, the food
doesn't stir itself as it heats.
Eggs also explode. Did you ever try frying an egg in a microwave? The
yolk tends to go BOOMPH! It seems that biological systems can adjust the
amount of dissolved gases within themselves. As long as the dissolved gas
is a bit lower than the natural amount, this will cause all tiny bubbles
to shrink and vanish. Tiny
bubbles will dissolve. This makes sense where living things are
concerned. You don't want your tissues to fill with foam! Given the
choice, Nature would rather make bubbles inside plants and animals slowly
shrink, not slowly grow.
So eggs, meat, and vegetables are "exploding coffee" too. Unless you
whisk some air into your eggs, they will tend to superheat and explode.
Same with potatoes, beets, etc. At least with vegetables you can slice
them thin. That gives them large surface area, and destroys any large
volumes which are far from the air. Meat is the same: it can explode if
overheated. Add some air by slicing it, or use a needle to poke it full
Q: I want to buy a microwave space heater!
Heh. Me too. Why aren't they available? One main reason springs to
mind: in your eyes, the cornea and internal lens are very sensitive to
heating. Unlike most other body parts, they have no blood vessels to
keep them cool. Intense
radio waves can give you instant cataracts, so a microwave heater would
require that we use special goggles to prevent blindness. Another
problem: a normal heater heats only your skin surface,
while a microwave
heater heats a very thick layer of flesh. So, with a normal heater
you can yank your hand away when you feel pain, and your thin skin cools
down almost instantly as the surface heat migrates to fill a thicker
layer. But with a
microwave heater, you might receive internal burns at the same time that
you feel pain on your skin. And when you yank your arm away, then the
thick layer of heated flesh wouldn't cool instantly, causing even more
tissue damage. And last, a microwave heater is an intense electrical
source, and it would probably destroy any radio, cellphone, PDA, or laptop
that came near. Lawsuit city!
But here's an interesting link found by Marcus:
Heating homes with microwaves
Q: Doesn't microwave energy lower the food's nutrition?
I don't know.
On the other hand, I've heard lots of crazy rumors
along the lines of "microwave energy turns food into slow poison." Maybe
it's true, or maybe all the rumors are just some BS made up by bored
storytellers. However, because these crazy rumors exist, we must be on
guard against believing them, and we should only trust information if we
can get it from people who
are up front about where the information came from in the first place.
Anything else, and we'd end up believing the liars who have fun by
starting rumors, hoping their rumors will catch fire and scare
huge numbers of victims.
Just follow the same rule that you follow for crazy spam emails that give
you all sorts of dire warnings about various topics. The rule: if the
warnings were real, wouldn't it be dead easy for the original email author
include several URLs pointing to many articles about the danger?
So, if an email doesn't link to real live websites, it's almost always a
false rumor being spread by hoaxers. And with any health warning, if
warnings about microwaves don't link to news articles or perhaps actual
medical journals, almost certainly the author is passing on third-hand
rumor rather than a story about a genuine hazard.
Below are a few of my own rumors! With no links to research or
I vaguely recall seeing something in the papers long ago about microwave
ovens harming food vitamins. But I don't remember if they said that
microwave-cooking is worse than REGULAR BOILING. I don't know if they
said that the problem comes from simple overcooking rather than from any
weird stuff with radio waves. I've always heard that eating raw
vegetables is best, and cooking destroys vitamins. What happens when you
feed people on overcooked or canned food for months? If somebody says
that microwave cooking is much MUCH worse than a canned food diet, I'd
like to find out WHY they say that. Maybe they're really just warning us
about boiled vegetables, but trying to make out like the problem is with
the microwave ovens rather than with the boiling. Microwave ovens cook
food deeply and quickly, so if you boil your vegetables for five minutes
on a stove, they'll still be green and crunchy, but if you boil your
veggies for five minutes in a microwave oven, they'll be way overcooked.
With microwaves, it's hard to cook only the outside surface of the
vegetables. (Now that I mention it, even boiling water doesn't do
such a great job. It's better to stir-fry veggies so the inside is
almost raw but the outer layer is cooked.
If we need to be warned about any cooking, the warnings must be precise.
And fake warnings themselves aren't innocuous. Don't forget, it was a
rumor-storm of fake warnings about poisoned candy and razor blades in
apples that ruined Halloween trick-or-treating in the US for decades
Another issue: microwave cooking is unsafe... COMPARED TO WHAT? Life is
unsafe. People die from taking showers or stepping on toys, not from
eating microwaved food. Think a minute. When you eat browned meat or
even baked bread, the browned parts are full of heat-shredded
biomolecules which form all kinds of NASTY CARCINOGENS. Yet they seem not
to harm people very much (perhaps we've all gotten used to the stuff over
the millenia because we've been eating charred food ever since humans
discovered fire.) As I understand it, browned food is a dark secret of
cancer studies, and if they applied the current FDA regulations to normal
foods like bread or BBQ, the government would have to ban cooking.
Browned foods have been "grandfathered in" to the cancer regulations. Yet
perhaps the carcinogens in browned
food do occasionally cause things like colon cancer? If they do, then
perhaps microwave cooking... is much SAFER than normal ovens? Since
cooking is akin to steaming? It's almost impossible to force your
microwave oven to shred the molecules on the outside of your steak into
tasty brown carcinogens. Instead you get steamed steak. MMMMM, healthy.
Does this mean that microwave ovens are health-food devices? Maybe
stores should've been selling microwave ovens next to the carrot juicers
and wheat-grass kits? I don't know. First I'd want to know if anyone
performed any microwave-cooking nutrition studies at all, even with lab
animals. And as a control, compare the results against such common health
dangers like going swimming or (gasp) DRIVING A CAR... or at least compare
it against baked bread and fast food hamburgers.
Q: Corona discharges? High voltage? Balderdash! The
watts per cm^2 is too small!
A: Wrong, melted pyrex breath! You're thinking about cooking
huge roasts. What happens with EMPTY microwave ovens?
Yes, a typical oven's output might only be 1000 watts or so. And yes,
1000W spread over a few hundred square centimeter does not proudce strong
e-fields. The fields will only be a few hundred volts per cm. (For
corona discharge we need around 30,000V/cm, a hundred times more intense.)
But you're forgetting
something important: the voltage rise for resonant circuits and standing
waves. If there's a
huge roast (a significant electrical load) then... 1000W leaves the
magnetron, and 1000W is absorbed by the meat. There's a 1000W energy flow
between magnetron and food, and the max. e-field inside the oven stays
On the other hand, if there's no food in the oven, then the 1000W bounces
back and forth, yet the magnetron still puts out more energy. This adds
to the waves already there. It's like wiggling your hand in a full
bathtub: energy is stored as standing waves, and the waves build up
higher and higher until frictional losses finally halt their growth.
Inside an empty microwave oven you might have 50,000 watts in one
direction and 49,000W in the other (with the magnetron supplying the 1000W
difference.) The interior of the oven is a resonator, and the peak
wattage within that space can become HUMONGOUS, since it only depends on
the "Q" factor of the resonator; it depends on the "friction" of the
system. Q is high, so huge wattage gives huge voltage. If there's no
food and no glass of water in the oven, then the e-fields become intense,
and the tiniest burr on a metal object can trigger the formation of a
large "Saint Elmo's Fire" which consumes hundreds of watts of RF energy
and resembles a blowtorch.
In fact, the empty chamber of a microwave oven is very much like the
secondary coil of a Tesla
Coil. The only major difference is the
operating frequency. RF energy is injected into the resonator, and the
output voltage rises and rises until finally the conductors get hot (or
until finally an electric arc breaks out somewhere.) Tesla coil
secondaries do this. Microwave ovens do this too. With nothing in the
oven chamber, either the metal walls and glass parts get very hot, or an
electric arc bursts forth from a sharp metal point somewhere inside the
Q: How do microwave ovens work?
A: OK, this question doesn't involve microwave oven myths, so
I guess this section is
becoming a FAQ. Microwave ovens are weird,
were born in a military "black project" dealing with exotic physics. The
microwave vacuum tube had its birth in England during World War II, and
was the central part of a new secret weapon: radar. Eventually the secret
military technology was declassified, and it ended up in appliance stores
everywhere. One is led to wonder how many other incredible military
discoveries are still sitting unused in that (perhaps) non-mythical
government warehouse seen briefly at the end of the first Indiana Jones
The Klystron and Magnetron microwave tubes both rely on nonlinear effects
of density waves in particle streams interacting with solid surfaces and
tuned cavities. That's right, they are identical to that bizarre
resonant-cavity standing wave generator known as the EMPTY BEER BOTTLE.
A microwave vacuum tube is like a whistle. Blow across a glass bottle's
and tiny sound waves within the bottle will cause the air jet from your
lips to move slightly. Motions of the air jet create pressure waves in
the bottle. Pressure waves wiggle the jet even more. Runaway feedback
takes place, and a loud sound is created. If we replace the air with an
electron stream in a vacuum, and use a hollow metal bottle, then radio
waves will build up in the bottle, and they will deflect the electron
stream back and forth. A microwave tube is an electron-whistle which
creates a loud "sound" in the form of radio waves. Intense sounds can
heat objects, and intense radio waves do the same.
If we start our electron-whistle operating, and then if we try to extract
energy, the resonance is ruined and only a little wave-energy comes out.
This problem was solved by using multiple "bottles" and a magnet to direct
the electron stream across their "mouths". A magnetron tube consists of a
central electron-emitter, one or two disk-magnets which cause the
electrons to swirl in a whirlpool motion, several tuned cavities with
their open mouths pointed into the whirlpool of charges, and a high
voltage power supply which moves the electrons along at high velocity.
Energy is extracted from just one of the tuned cavities, and this has only
a small effect on the resonance of the others.
If you wanted to create an acoustic model of a microwave oven, you could
attach a vacuum cleaner to the center of a heavy cylindrical box. Put
slots around the edge of the box. The resulting tornado acts to supply the
jet of high-speed air that will "play" the bottles. Several glass bottles
could then be poked through the sides of the box, inserted into the
tornado, and adjusted to give a loud sound. With luck, you might even be
able to connect an "exit tube" to one of the bottles, connect the tube to
a sealed metal cabinet, then actually heat any objects which are placed in
the cabinet. Use really thick, heavy construction materials, otherwise
the intense sound would not stay trapped inside your beer-bottle-tron
device. It would sound like an air-raid siren.
The speed of light is about one million times faster than the speed of
sound. However, audible sound is about a million times lower in pitch
than microwaves. The effects cancel out, so the wavelength of the sound
waves in glass bottles would be very similar to microwave wavelength. So
instead of giving out 1,000 MHz microwave radiation, your device would
give out sound radiation that's a few inches in wavelength (just like
microwaves,) but a million times lower in frequency, or about 1000 Hz.
Q: I nuked the fruit flies on the food, but they survived!
I noticed the same thing. There are several possibilities.
First, the pattern of heating inside the oven is NOT uniform: there are
hot spots and cold spots, and most important: the hot spots don't touch
the metal walls. If a bug crawls on the oven's inner surface, it's fairly
safe. Also, if you're
cooking a large hunk of food at the time, then this food absorbs the RF
energy like mad, and insects won't get as hot as when the oven is totally
empty. Also, insects have built-in behavior to avoid being cooked by
sunlight... if they feel hot, they crawl faster, and if the heat stops,
they stop too. Perhaps when you turn on the oven, all the bugs move until
they hit a cold spot in the radio wave pattern, then they stay in that
spot. (So if a bug was on the rotating glass platter far from the metal
walls, then it's out of luck.)
Q: I tried making "microwave ball lightning." It didn't work.
For better results, try it with
Crowley's discovery, carbon fiber: carbon "veil" from a
plastics supplier or fiberglas supplies store. JL Naudin finds that the
sharp carbon stick from a mechanical pencil also works well.
Q: The turntable rotates randomly? Why?
The demo with the burning candle requires a microwave oven with a
turntable inside. The turntable carries the candle into a "hotspot"
in the oven, then plasma bursts forth. Without a turntable you might have
spend twenty minutes moving the candle to different spots. Also, I find
that my 1000 watt oven makes plasma flares very easily, but an older
500-watt version might not have the gusto. Try using a newer, "hotter"
high wattage oven. Also, sometimes all the hotspots are a certain
the glass plate. If your stubby candle won't make BL, try propping it up
on a wood block or an overturned bowl. Try different heights.
I suspect that the "ball lightning" needs both a Saint Elmo's fire and a
source of chemicals in order to get going. Sharp pieces of metal
sometimes produce microwave arcing, but it's unreliable. A charred
toothpick is a conductor, and also it has incredibly sharp points (the
carbonized wood fibers.) This might be why a normal candle doesn't make
fireballs, but a candle with charred toothpicks near the flame DOES. Or
perhaps the charred toothpicks contribute ions? Maybe instead use
uncharred toothpicks which are wetted with salt water?
Here's a question of my own: if you try to catch a fireball in an
upside-down glass chemist's funnel, does the plasma pour up through the
funnel's thin tube? Could it even escape from the oven if you drilled a
hole in the oven top to pass the glass tube? PLASMA TORCH! I haven't
tried this one myself.
A great mystery within microwave ovens: WHY DOES THE TURNTABLE
SOMETIMES ROTATE BACKWARDS? I always wondered about this. The obvious
explanation is that the turntable motor is a 60Hz synchronous induction
motor. But why? Synchronous motors aren't as good as the normal kind.
One thing might make sense: it forces your turntable to end up in the same
position as it started. That way your coffee mug will be at the front, or
the handles on the cassarole dish will be positioned correctly. But my
microwave oven doesn't do this. Most of the time the mug ends up in a
Testing is required. I heated a mug of tea at
a minute, and for the first time I actually watched the clock as the
turntable rotated. AHA! IT ROTATES ONCE EVERY TEN SECONDS!!!! I verified
the effect and it does work: as long as you punch in multiples of 10 seconds,
your food will come back to its original position. But something's
screwy. My oven at home doesn't do this, yet its turntable randomly
starts off clockwise or CCW, so it must contain a synchro motor. So I
timed the oven at home. Bingo: it rotates every 20 seconds. That
explains everything. At home, if I punch in 30 seconds, or 10 seconds,
then the turntable rotates an extra half turn, putting the soup bowl on
the opposite side. Not too smart. How many people cook things for 20
seconds, or 40 seconds? A 3RPM turntable speed only works if you
cook something for one minute. But now that I know about the problem, I
can start only using multiples of 20 seconds.
Dr. L. Bloomfield's Microwave Oven FAQ