In article >, Bob Pastorio
> wrote:


> >>>>>But this one is true! It may be over-simplified, but, in comparison=
> to
> >>>>>regular ovens, which heat only from the outside, microwaves penetrat=
> e the
> >>>>>food and heat it from the inside also.
> >>>>
> >>>>Not really. Microwaves are energy sources and, as such, need to=20
> >>>>penetrate from the outside. They do penetrate more deeply (in meats, =
>
> >>>>no more than about 1 1/2 inches) than radiant heat or convected heat =
>
> >>>>in conventional cooking sources.
> >>>>
> >>>>It means that they're heating a bit under the surface simultaneously =
>
> >>>>as the surface. But there's still more energy at the surface.


But the surface is exposed to the cool air, thus cooling it down. As I
posted, the claim is an over-simplification. However, I think that it is
a useful explanation as to why microwave cooking is different than using a
conventional oven. A good example is a potato. It takes a long time to
cook a potato in a conventional oven. A potato cooks very quickly in the
mw, but doesn't have that same skin because it has been cooked on the
inside at the same time the outside was cooked, and it didn't have that
dry heat that crisps the skin.


Lots of good info down below. I've snipped what I agree with or don't
know about.



> Here's an article I wrote a while back about microwaves.
>
> Microwave mysteries exposed
>
> Here's one of the new, persistent falsehoods - microwaves cook from=20
> the inside out.
> That's just plain wrong. Period. Not my opinion, here; the
laws of=20
> physics.
> Microwave energy has to pass through the outside of food before it=20
> can get to the inside, just like any other kind of energy and the=20
> normal penetration is between 3/4 and 1 =BD inches. No more. Don't=20

Microwaves only give up their energy when they are absorbed by the
molecule. A microwave that passes through the exterior does not heat it
up. More energy will be absorbed by the exterior, but not by a
significant amount.


> believe me? Try this. Put a five-pound beef roast in the mike and=20
> fire it up. After about five minutes, pull it out, cut it in half and=20
> feel the cut surface. Here's what you'll find: the outside is hot=20
> and the center is still cold.


We are in agreement that anything thicker than the penetration of the
microwaves cannot be cooked by the microwaves. The center must be cooked
by the conduction of heat from the part heated by the microwaves.



> explanation. Textbooks on physics say that "microwaves" are very=20
> short waves of electromagnetic energy. Short compared to what? The=20
> light of the sun or radio waves, both of which are also=20
> electromagnetic energy. Those tall radio station transmitter towers=20


As you say, microwaves are simply very short radio waves. However, light
is *much* shorter than microwaves. The length of light waves is measured
in angstroms, which are one hundred-millionth of a centimeter.



> broiler, you heat the outside of a steak and the heat is carried=20
> (conducted) through the meat to the center. Same with microwaves -=20
> with the one condition that, misunderstood, may have helped create the=20
> error mentioned at the beginning of the article. Where the microwaves=20
> penetrate food, there is heating going on both at and right under the=20
> surface at the same time.


Most of the time, microwaves cook primarily through excitation of the
molecules. Cooking by conduction is a minor part of microwave cooking.
Cooking by conduction is better done with a conventional stove.



> complicated than that. The voltage of your house determines how fast=20
> and consistently you'll cook. The voltage will differ depending on=20
> which power company provides your electricity. It will also change=20
> depending on time of year, time of day and other Murphy's Law=20

I don't believe that voltage fluctuations would make a big difference.
Voltage is pretty standard, other than brownouts. The power rating of the
stove and the accuracy of measurement of ingredients would be bigger
factors.



> * The same food cooked in two different casserole-type dishes will=20
> cook faster in a shallow, wide one than a deep, narrow one. It's=20
> simply a matter of how much surface area is exposed; wide lets more=20
> surface show.


Surface area is not relevant. Microwave ovens are designed to scatter the
microwaves all through the oven. The microwaves penetrate the food from
all sides, including the bottom.

--
Dan Abel
Sonoma State University
AIS