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Elevation and Cooking
Name: Victoria M.
Status: student
Age: 18
Location: N/A
Country: N/A
Date: 12/7/2004
Question:
Why is it when you are on a mountain cooking something it
takes longer to cook or it does not cook and why is it, when you have a
pressure cooker it takes the exact same time?
Replies:
I assume your question refers to something being cooked using boiling water.
Water boils at a lower temperature at higher altitudes because of the lower
air pressure. If you cook noodles at sea level, the boiling water heats the
noodles to 100C. When a molecule reaches that temperature it vaporizes and
leaves the mixture. At 5000 feet it would begin to boil at a lower
temperature so you are cooking your noodles at a lower temperature.... and
it will take longer.
If you use a pressure cooker the pressure inside the cooker becomes higher
than the ambient pressure causing the water to boil at and the noodles to
cook at a higher temperature.
If you want to check this out, use a thermometer and check the temperature
of boiling water at a lower elevation and then later at a higher elevation.
The temperatures will differ.
Larry Krengel
Hi Victoria,
You answered your question yourself with "pressure". On a mountain top the
air pressure is a little lower. If you ever went on top of one you might be
one of those unfortunate souls who suffers from altitude sickness, gasping
for breath. Strange how a little less pressure and a little less atmosphere
can effect us so much.
Anyway, back to cooking. At higher elevations water boils at a little lower
temp than 100 C. What this means is that if it boiled say at 80 C you cannot
get it any hotter, it is boiling already. So say you wanted to cook some
spaghetti. If you put your spaghetti in a cold water in a pot overnight,
eventually it would get soft enough to eat. It would be cold, but you could
eat it. On a mountain, cooking takes longer because it is like cooking on
medium heat instead of leaving the burner on high. Either way it will cook,
one will take longer than the other.
In a pressure cooker, you let a good head of steam build up. The top is
locked and sealed so that the pressure inside is actually greater than the
pressure outside. The little weight you put on the valve takes care of that.
Now comes the cool physics. If lower air pressure means lower boiling
temperature, higher pressure must mean, ???? That is right a higher
temperature to boil! Higher temp when cooking equals faster cooking.
All you have to do is follow the pressure cooker's directions. Turn down
the heat after the weight starts to jiggle. If you pop the safety valve,
all the stuff inside will come spewing outside, at a very high
temperature! (This
happened to my mom when I was a kid. She did not hear the thing jiggle, it
got too hot and "thar she blew". We had ham juice on the ceiling. What a
mess.)
So cook safely when using that pressure cooker! My mom still would rather
use the pressure cooker than the microwave. Isn't science in the kitchen
fun?
Martha Croll
The boiling point of water in mountainous areas is lower because of a
decreased air pressure (compared to sea level) at higher altitudes. A
pressure cooker provides an artificial environment independent of the air
pressure outside the vessel.
Pat Rowe
At altitude, water boils at a lower temperature, so the maximum temperature
you will get in your open pot is the lower boiling point.
In a pressure cooker, the pressure is controlled in part by the relief
valve, so although the pressure (an thus the boiling point) inside the
cooker may be affected at altitude, it is less so than in an open pot.
Don Yee
I am imagining that you are talking about cooking something that requires
water - such as pasta or rice or soup. So here is something to think about:
what is the air/atmospheric pressure on top of a mountain relative to that
at the base of the mountain? How will this affect the boiling point of the
water - will it be higher or lower?
Greg (Roberto Gregorius)
Hello,
Cooking requires maintaining food at a given high temperature for a given
period of time. Food is under- or overcooked when this balance is not
maintained.
As you may expect, it takes longer to cook food at lower temperatures.
Inversely, if we maintain a high temperature, food cooks faster.
Most foods have a substantially amount of water, and are cooked in
water. How hot this water can get depends on the surrounding pressure. At
sea level, air pressure is about one Bar (referred to as the atmospheric
pressure.) At this pressure, water boils at ~ 100 degrees C (or 212 F) and
cannot get hotter (it will evaporate instead). On higher grounds, air
where air pressure is less than one bar, water boils at lower
temperatures, and cannot get as hot as at the sea level temperature of 100
degrees C. That is why it takes longer to cook at higher elevations.
In a pressure cooker, a much higher pressure can be maintain and thus
water can be heated to higher temperature without boiling off. Many
consumer pressure cookers maintain a pressure of one bar ABOVE
atmosphere, i.e., an absolute pressure of two bars. As a result, water
reachers a temperature of about 120 degrees C (or 250 F), and food is
cooked faster.
Incidentally, one may also speed up cooking somewhat by cooking in oils
that have boiling temperatures above 100 degrees C.
AK
Ali Khounsary, Ph.D.
Argonne National Laboratory
Hmmmm, maybe pressure has something to do with it....
As you go up in altitude, atmospheric pressure goes down. The more pressure
on a gas, the less volume there is (Boyle's Law) and the more often the
molecules bump into each other and the sides of their container. This
creates
heat. There is another gas law that states that increasing the amount of
pressure increases the temperature. The opposite is also true. So the less
pressure, the less temperature. So at higher altitudes, foods need to
cook longer
to cook to the same degree of "doneness". If you are able to control the
pressure however, as in a pressure cooker, the foods will cook all the way.
Van Hoeck
The temperature at which water boils depends upon the applied pressure. On
a tall mountain the applied pressure is less than it is a sea level (1
atmosphere) so the boiling temperature is less than it is at sea level. In
a "pressure cooker" it is possible to control the applied pressure
regardless of the pressure outside the cooker itself. So even on a tall
mountain the applied pressure within the cooker can still be 1 atmosphere
(or even more) regardless of the surrounding pressure of the atmosphere.
Vince Calder
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Update: June 2012
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