# I've a physics question about pressure cookers **URL:** \ **Category:** Factual Questions\ **Created:** [March 13, 2012, 10:01pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692 "2012-03-13T22:01:00Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![janeslogin](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@janeslogin](https://boards.straightdope.com/u/janeslogin)\ **Post date:** [March 13, 2012, 10:01pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/1 "2012-03-13T22:01:00Z")
If a pressure cooker is at 15 psi does the altitude matter? Is the boiling temperature at 15 psi inside the cooker the same irrespective of altitude? ---
**Author:** ![Simplicio](https://avatars.discourse-cdn.com/v4/letter/s/c37758/32.png) [@Simplicio](https://boards.straightdope.com/u/Simplicio)\ **Post date:** [March 13, 2012, 10:06pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/2 "2012-03-13T22:06:57Z")
I’m pretty sure the pressure given by the gauge is the differential between the outside of the cooker and the inside. So when the cooker is open, it reads zero, not the actual atmospheric pressure. So then yes, at different altitudes, the actual pressure in the cooker will vary and boiling temps will also change. ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [March 13, 2012, 10:11pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/3 "2012-03-13T22:11:05Z")
Not if the pressure is relative to the pressure outside the cooker, but I don’t know of any cookers that use absolute pressure (but then 15 PSI would be only slightly higher than sea level pressure, which is 14.7 PSI). ---
**Author:** ![RearEchelon](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@RearEchelon](https://boards.straightdope.com/u/RearEchelon)\ **Post date:** [March 13, 2012, 10:28pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/4 "2012-03-13T22:28:59Z")
Being that the cooker (when cooking) is a closed system, I would think that the boiling temperature inside would be the same regardless of outside pressure, but I could be wrong. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 13, 2012, 10:30pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/5 "2012-03-13T22:30:48Z")
As the other posters have alluded to, the pressure inside a pressure cooker is “gauge” pressure, which means it’s measured relative to the surrounding atmosphere. So, yes, the altitude matters. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [March 13, 2012, 10:39pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/6 "2012-03-13T22:39:59Z")
stove top weight regulated ones would be in reference to local pressure. stove top spring regulated ones would be independent of local pressure. ---
**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\ **Post date:** [March 13, 2012, 11:46pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/7 "2012-03-13T23:46:15Z")
> [@johnpost](#): > > stove top weight regulated ones would be in reference to local pressure. > > stove top spring regulated ones would be independent of local pressure. Doesn’t matter. Either one (spring or weight) is pressing against the surrounding atmosphere, so the correct answer is that it does depend on the surrounding atmospheric pressure. excavating (for a mind) ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [March 14, 2012, 12:05am UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/8 "2012-03-14T00:05:32Z")
> [@janeslogin](#): > > If a pressure cooker is at 15 psi does the altitude matter? Is the boiling temperature at 15 psi inside the cooker the same irrespective of altitude? I think others have answered this, but here’s a practical example. When the wife and I do pressure canning the instructions say for us to run the canner at 13 PSI because we’re at 5300ft, instead of 11 PSI at sea level. The recipe (vegetables, meat, etc.) and jar size (1 pint or 1 quart) effect the total time at pressure, but the altitude effects the pressure maintained. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 14, 2012, 12:07am UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/9 "2012-03-14T00:07:49Z")
> [@echoreply](#): > > I think others have answered this, but here’s a practical example. When the wife and I do pressure canning the instructions say for us to run the canner at 13 PSI because we’re at 5300ft, instead of 11 PSI at sea level. The recipe (vegetables, meat, etc.) and jar size (1 pint or 1 quart) effect the total time at pressure, but the altitude effects the pressure maintained. _Affect_. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [March 14, 2012, 1:29am UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/10 "2012-03-14T01:29:54Z")
> [@beowulff](#): > > _Affect_. My training is in psychology, so I use _affect_ to describe an expressed emotion, and _effect_ for everything else. Then I’m only wrong occasionally. Hmm, I’d be more satisfied if I could’ve worked some apostrophe abuse into that sentence. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [March 15, 2012, 10:02pm UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/11 "2012-03-15T22:02:46Z")
The counterweight releases the steam from the pressure cooker when the pressure difference between the inside and outside multiplied by the area of conterweight equals the weight of the counterweight. At higher altitudes, the outside pressure is lower, so the inside pressure needed to release the weight is smaller. ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [March 16, 2012, 5:12am UTC](https://boards.straightdope.com/t/ive-a-physics-question-about-pressure-cookers/615692/12 "2012-03-16T05:12:59Z")
> [@excavating\_for\_a\_mind](#): > > Doesn’t matter. Either one (spring or weight) is pressing against the surrounding atmosphere, so the correct answer is that it does depend on the surrounding atmospheric pressure. > > excavating (for a mind) So I can assume that the spring variety is not sealed to the atmosphere, then? Otherwise, its reading would be irrespective to altitude, no?