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Old 06-01-2015, 06:01 PM   #31
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Originally Posted by Selkie View Post
RPCookin said: "The point of the pressure cooker is to create a higher pressure in the cooker. Just because the ambient pressure is less, does the pressure cooker pressurize less too?"
Yes. The pressure relief valve (the part that goes Hssssss...." relieves the pressure differential between the inside and outside of the pressure cooker. If it's set for 10 pounds (just an example), it will release the pressure 10 p.s.i. above the ambient pressure, no matter what the local pressure is.
In short, local altitude does matter.
What you say could be correct, if the pressure exerted by the outside ambient pressure determined the force placed on the pressure regulator. But at least in both of my pressure cookers, there are weights that regulate the pressure. It takes 11.5 lbs. psi to lift the weight of the regulator to allow steam to escape. My larger Pc has added weight rings that can be added so that the internal pressure of the pot requires 11.5, 12, or 15 lbs. of internal pressure to release steam, regardless of the ambient atmospheric pressure. The deciding factors are the rigid, closed pot, and the weighted pressure regulator. The inside conditions of the pressure cooker are isolated from outside conditions except for gravity. If you were on the moon, it would take much less pressure to cause the PC to release pressure, but that is because the regulator would weigh less due to a weaker gravitational field, not because the PC is in a vacuum.

If the PC were a semi-flexible container, then yes, outside pressure would make a dramatic difference.

Water boils at a lower temperature in an unsealed pot because there is less atmospheric pressure. But the PC develops its pressure by lifting a weight. The difference in the weight of the regulator between 5000 feet, and sea level is negligable, and so the internal pressure of the pot should be the same regardless of the elevation you are cooking at.

I concur with the post that suggests a poor seal between the lid and the pot, or maybe a faulty pressure valve, if your PC has one.

In answere to GG's question, I sometimes cook my rice on the stove top, in a covered pot, sometimes in the rice cooker, and sometimes in the PC, depending on other factors. The PC is not any more work than the other methods, and shortens the cooking time required, which can free me to get other things done, as that burner is available to me for reuse sooner.

Why, I've even been known to pre-cook my rice, and heat in later in the microwave.

There are valid reasons to use the PC, just as there are valid reasons to cook a specific rice pilaf that we make on the stove top rather than in the oven, in a casserole dish as the recipe was first given to us. Sometimes though, using the casserole dish is the better choice, again, depending on other factors. And the cookinhg period from removing the PC to opening the lid, when I place the unopened PC under cold running water is less than 30 seconds, litteraly.

To know many techniques is to allow greater creativity, and better time management. It gives you flexibility.

Oh, one thing that will affect time is outside ambient temperature. The cooler it is in your home, the more time that will be required to bring the PC up to sufficient temperature to develop the required cooking pressure, and more energy will be required to keep it there. The pot radiates heat, as well as absorbing it. The greater the difference between the temperature of the metal, and the air, the faster the pot will radiate heat from the pot.

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Old 06-01-2015, 06:01 PM   #32
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RPC.......But if the ambient pressure is lower then there is less pressure "weighing" that plug down against the relief hole, I would think....
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Old 06-01-2015, 06:15 PM   #33
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RPC.......But if the ambient pressure is lower then there is less pressure "weighing" that plug down against the relief hole, I would think....
The size of that plug wouldn't create enough pressure difference to cause dramatic change.

If you have a container whose lid is say, 100 square inches in size, then if you pump 15 lbs of pressure into the container, the lifting pressure on the lid would be 100, times 15, or 1,500 psi. The average pressure regulator probably has less that a squate inch of area on which the atmospher can exert force. Let's say we have an average atmospheric pressure of 10 lbs. per square inch, and the regulator has an area of .5 inches. The pressure exerted on the regulator is 5 lbs. psi, and it is exerted on top, on the sides, and underneath the reculator, and so has virtually no affect on the pressure regulator. The inside temperature however, exerts its energy in one direction, to lift the regulator upward. It has no force to counter that lift except gravity.

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Old 06-01-2015, 06:52 PM   #34
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In that case, I'd call the recipe a failure and stop trying to make it. Even if it did cook in 5 minutes, you still have to wait 15 minutes for the pressure to diminish, which is the same amount of time it takes to make rice in a regular saucepan.

Not every Internet recipe writer knows what they're doing.
Well, my "recipe" is terribly simply: grained rice, and just that , and I of course need it for many many kinds of meal, so I still have to look for the best solution for me, even if it consist of buying a new cooker, that's why I asked the brand of cooker all of you use. But I sincerely thank your help and opinion, and the other's,.
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Old 06-01-2015, 07:08 PM   #35
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The size of that plug wouldn't create enough pressure difference to cause dramatic change.
Yeah, good point there.... as in an almost completely closed pressure chamber.
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Old 06-01-2015, 07:30 PM   #36
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If someone is using a pressure cooker with a gauge instead of weights, I think the possible effects of altitude would be irrelevant. Well, except it might still take longer to get up to pressure.
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Old 06-01-2015, 07:37 PM   #37
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Gravity has nothing to do with it. Atmospheric pressure altitude is the determining factor and is more significant than most people realize.
When compared with sea level, a person at 5,000 ft. altitude experiences a pressure loss of 15%. At 10,000 ft. you've lost 30%, so instead of your 11.5 pounds of internal pressure of your pressure cooker, you're only cooking with 8.05 pounds of pressure before the relief valve begins to open.
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Old 06-01-2015, 07:52 PM   #38
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Well, my "recipe" is terribly simply: grained rice, and just that , and I of course need it for many many kinds of meal, so I still have to look for the best solution for me, even if it consist of buying a new cooker, that's why I asked the brand of cooker all of you use. But I sincerely thank your help and opinion, and the other's,.
A recipe includes the instructions to make it. The recipe you're using is not working for the conditions you're cooking under. I think medtran's suggestion to ask someone who lives near you for advice is a good one.
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Old 06-01-2015, 07:56 PM   #39
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A recipe includes the instructions to make it. The recipe you're using is not working for the conditions you're cooking under. I think medtran's suggestion to ask someone who lives near you for advice is a good one.
That's the smartest idea yet!
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Old 06-01-2015, 09:27 PM   #40
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This site explains what happens in a pressure cooker quite nicely. But to understand it you should have a little physics background. And yes, the weight of the regulator cap determines the inside pressure of the PC.

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