Microwaves and how they work.
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The microwave oven is one of the great inventions
of the 20th century -- millions of homes in America have one. Just
think about how many times you use a microwave every day:
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You're running late for work, so there's no time to fix
breakfast at home. On your way to the office, you stop to gas up your
car. Inside the quickie-mart, you grab a frozen breakfast burrito and
pop it in the microwave on the counter. Later that day, you have to
work through lunch. By 3:00 p.m., you're starving, so you grab a
snack-pack of microwaveable
popcorn
from the vending machine and pop that in the break-room microwave. That
night, after a really long day at work, you're simply too tired to
grill out, so you dish up last night's
lasagna and heat it up in the microwave...
As you can see, microwave ovens are popular because they cook
food in an amazingly short amount of time. They are also extremely efficient in their use of
electricity because a microwave oven heats
only
the food -- and nothing else. In this article, we'll discuss the
mystery behind the magic of "meals in a minute" with microwave cooking.
A microwave oven uses
microwaves to heat food. Microwaves are
radio waves.
In the case of microwave ovens, the commonly used radio wave frequency
is roughly 2,500 megahertz (2.5 gigahertz). Radio waves in this
frequency range have an interesting property: they are absorbed by
water, fats and sugars. When they are absorbed they are converted
directly into atomic motion -- heat. Microwaves in this frequency range
have another interesting property: they are not absorbed by most
plastics, glass or ceramics. Metal reflects microwaves, which is why
metal pans do not work well in a microwave oven.
Microwave cooking
You
often hear that microwave ovens cook food "From the inside out." What
does that mean? Here's an explanation to help make sense of microwave
cooking.
Let's say you want to bake a cake in a conventional
oven. Normally you would bake a cake at 350 degrees F or so, but let's
say you accidentally set the oven at 600 degrees instead of 350. What
is going to happen is that the outside of the cake will burn before the
inside even gets warm. In a conventional oven, the heat has to migrate
(by conduction) from the outside of the food toward the middle. You also have dry, hot air on the outside of the food
evaporating moisture. So the outside can be crispy and brown (for
example, bread forms a crust) while the inside is moist.
In
microwave cooking, the radio waves penetrate the food and excite water
and fat molecules pretty much evenly throughout the food. No heat has
to migrate toward the interior by conduction. There is heat everywhere
all at once because the molecules are all excited together. There are
limits, of course. Radio waves penetrate unevenly in thick pieces of
food (they don't make it all the way to the middle), and there are also
"hot spots" caused by wave interference, but you get the idea. The
whole heating process is different because you are "exciting atoms"
rather than "conducting heat."
In a microwave oven, the air
in the oven is at room temperature, so there is no way to form a crust.
That is why microwavable pastries sometimes come with a little sleeve
made out of foil and cardboard. You put the food in the sleeve and then
microwave it. The sleeve reacts to microwave energy by becoming very
hot. This exterior heat lets the crust become crispy as it would in a
conventional oven.
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