Gavin Stairs on tue 13 jan 98
At 01:41 PM 1/12/98 EST, you wrote:
....
> Now there's the problem that microwaving changes food; particularly
>proteins. You don't get out what you put in. I don't have details but expect
>we'll be hearing more about this. And then there's radiation. . .
You should say that cooking changes food. There's nothing particular about
the way microwaves cook food that I'm aware of. Get protein or starch up
to a certain temperature, and presto! a chemical change will occur. That's
what we have been doing to our food for, oh, such a long time.
Radiation: microwave radiation is just the same as light, only at a lower
frequency. Above light (in frequency) there's ultraviolet, and above that,
x-rays and gamma rays. Below light (in frequency) there's infra-red, then
long wavelength infra-red, which is sensible heat. That goes on for a bit,
and then we get to microwaves, and then a bit more and we're at radio
waves. All of these phenomena are the same spectrum, the same fundamental
physical mechanism. One region grades into the next.
However, different spectral regions interact with matter in different ways,
according to the resonance phenomena that govern in the region of interest.
Gamma rays interact principally with the core of the atom, the nucleus.
X-rays with the electrons that are associated with atoms. Ultra-violet
interacts principally with the valence electrons in certain compounds.
These are the electrons that govern chemical reactions, so ultra-violet
radiation changes chemical compounds: for instance it gives us sun-burn,
and fades paint pigments and dyes. Visible light also affects some
compounds with weakly held electrons, particularly dyes and some metastable
salts, such as are used in photography. Things sensitive to light are
called actinically sensitive. Infra-red radiation is not energetic enough
to directly change any but a few compounds. Long infra-red is heat
radiation, and you can feel it on your skin, but not see it. It is only
very weakly directly active on chemical compounds. Microwaves are still
less so.
Heat can produce chemical changes, so infra-red can induce chemical change
indirectly, by heating the chemicals. The same mechanism is responsible
for micro-wave cooking. The microwaves excite certain molecules, which
become hot, and transmit the heat to the mass of food. It is mainly the
water and fats in food that heat up in microwaves, but proteins and
carbohydrates can also be heated this way. Also some ferric compounds such
as may be found in clay.
Since the cooking happens because of the heat, there is no fundamental
difference between microwave cooking and cooking in an oven, except for the
fact that the microwaves tend to penetrate to the centre of the object,
while the heat of an oven (infra-red and convective transfer) is deposited
mainly on the outside. So an oven dehydrates and browns the outside, while
microwaves do not. In fact, you can actually dehydrate and brown the
inside of a microwaved dish before the outside is cooked, as I have found
out by experiment.
In fact, since infra-red radiation is more energetic than microwaves, there
is a slightly greater risk of changing certain compounds by direct
stimulation with infra-red (ordinary cooking) than with microwaves.
There is ongoing research to determine if there may be indirect effects
from microwave radiation in living beings. You may know that some diseases
make people sensitive to light, so that infra-red and/or visible light
cause undesirable reactions in their skin and blood (e.g., porfyria). This
happens by direct stimulation of certain resonant sites on specific
compounds. Very subtle and tricky reactions. Similar reactions may occur
with microwaves and even longer wavelength radiation, but this has little
to do with cooking. Such changes occur in profusion when something is
cooked. The bioactive changes are a much subtler thing, and less acute
than, say, a burn. Such effects may have significance on growth (over long
periods of exposure) and brain activity (which is, after all, electrical,
and should be somewhat susceptible to radio waves like microwaves). In
respect of growth and developmental abnormalities, there is interest in
those living in power line frequency fields (virtually all of us) which are
very much less energetic than microwaves. There is some evidence for this,
but I'm not aware of anything definitive. In respect of brain activity,
there is interest in the effect of cell-phones, which transmit in the
microwave region, and which some people use while driving, and for long
periods of time.
We live in a sea of radiation, and at least some of it is essential for
life. There is no reason to suppose that microwaved food is more dangerous
than, say, char-broiling, or toasting. It is more like steaming, which is
usually held to be very wholesome, and preserving of nutrients. Those that
are not destroyed by any kind of cooking, that is. I personally have much
more concern about ultraviolet over-exposure, which gives sunburn and long
term susceptibility to melanoma. The sun has been with us for a long time,
and we have survived its daily bath quite well, uv or not.
Gavin Stairs
Toronto, Canada
C du Bee on mon 19 jan 98
so, what would happen if I put dry green ware into a microwave oven and cooked
it on high for say, 20 minutes?
Paul Monaghan on tue 20 jan 98
C du Bee,
Picture what is happening in the material. the Microwave energy
vibrates the bonds of the water molecule producing heat from friction.
As the heat increases the water molecules separate - turn into steam-
and escape as a gas. If this happens very slowly the greenware will dry
out. However, if it happens too quickly you will get cracks and the
greenware will shatter or a t least break. try it on very low power for
longer periods of time and monitor the surface temperature of the
greenware. this would be similar to warming the kiln for a day before a
firing.
Paul :-)>
C du Bee wrote:
> ----------------------------Original
> message----------------------------
> so, what would happen if I put dry green ware into a microwave oven
> and cooked
> it on high for say, 20 minutes?
Robert Katz on tue 20 jan 98
I would venture that you do not value your microwave very much.
Vicki Katz
Katz Creek Pottery
At 10:06 AM 1/19/98 EST, you wrote:
>----------------------------Original message----------------------------
>so, what would happen if I put dry green ware into a microwave oven and
cooked
>it on high for say, 20 minutes?
>
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