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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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