While not a big hitter in terms of saving energy, we have picked up a couple different sized pressure cookers (second hand). Here are some of the reasons:
1. You can cook BROWN rice in 18 minutes!!! (we almost never have brown rice because it takes 45 minutes). Everything cooks faster under pressure, on average it cooks 70% faster. It doesn't take much gas to maintain the pressure.
2. It will can all kinds of foods. We have been investigating ways to "preserve the harvest", pressure canning is a good way to preserve non-acidic foods.
3. Food retains more nutritional value.
4. Since food cooks faster and you only have to heat up a small amount of water (weather cooking or canning) , it is much more efficient.
Bill, correct, I think the 15 psi weight brings the temp up to about 250F, which also kills a lot more wee beasties than 212F.
This graph only goes to 10 psig, but you get the idea. Up by CO, at maybe 10000 feet, the water boils at around 195F without pressurizing it. You can also get water to boil at room temp by applying a strong vacuum, but it won't cook anything
Well, I've never been "brave enough" to try canning (I suppose I have a fear of botulism if you make a mistake), but I very much like having a pressure cooker as well. As far as I can tell, pressure cookers sort of fell out of favor once microwaves became cheap/popular. However, while a microwave does a better job of heating foods than a pressure cooker (which is one reason I use my microwave more than my pressure cooker), the pressure cooker still is the clear winner at quickly "tenderizing" whatever you are cooking. For example:
1) Take a cut of cheap (very) tough meat, and put it in the pressure cooker with a cup or two of water. 45 minutes of pressure (15psi), and you have a surprisingly tasty "roast", that is so tender it flakes apart with a fork!
2) Dry beans of any sort also cook (so they are VERY tender) in about 45 minutes of pressure WITHOUT having to pre-soak them first (i.e. just stick them in dry from the package). Want a really nice "home made chilly" on the cheap? Use a pressure cooker. Like a home made bean soup? Pressure cooker again. Like Indian lentils? Pressure cooker again. You get the idea...
3) Rice seems to cook in about 15 minutes of pressure. And you can also dump in any flavors you want at the same time. For example, we sometimes make a really nice/fancy "Spanish rice" by dumping in rice, water, tomato sauce, spices, a few veggies, etc, and just letting it all "stew" for 10 to 20 minutes of pressure. The resulting meal is ready to eat (and tastes like it cooked all day) after removing the pressure lid, giving it a stir (to mix the water and solids), and letting it set for about a minute (to cool, and also for the rice and other solids to absorb the water they couldn't take in when they were pressure cooking).
4) Making a big batch of potato salad and/or "mashed potatoes" is also easy. In that case, you just cooked washed potatoes (peels still on) for either 10 minute (potato salad) or 15 minutes (mashed potatoes) of pressure. Then you can take them out and cut them (and also peel them, if desired) with a butter knife (they fall apart that easily). And you even get some of the minerals of the skins infusing into the potatoes themselves (improving flavor, color, and health value).
4.5) Sometimes I like roast and potatoes. So I pressure cook the meat for about 30 minutes, than quickly bring down the pressure. I then plop in raw (washed, but not peeled) potatoes, carrots, and onions, on top of the meat (which is still in the pressure cooker) and again pressure cook for about 15 minutes of pressure. At that point everything is done, and I have a full "meat and potatoes" dinner ready to dish out of the pressure cooker. And the veggies already have the meat flavor infused into them (since they cooked together), so you don't even need to worry about gravy (just a little butter, and maybe a dash of sour cream). Yum...
5) Have an old "picked to the bone" turkey you were using for "turkey dinner"? Plop the (already cooked) remaining bones into a pressure cooker and give it a few minutes of pressure. Guess what? The bones will come apart at the joints, and all the hidden meat will be exposed. You can then remove (pick out) the bone fragments, and use the resulting (meat heavy) broth to make a home made turkey soup!
Etc. (you get the idea)
Unless you are doing a "soup", be sure to use much less water than you normally would. Remember, a pressure cooker actually traps most of the water in the pan, so you won't have anywhere near the evaporation you would normally get (with say "boiling" in a normal pan). Essentially "pressure cooking" is really much closer to "steam cooking" (albeit steam cooking under pressure) than normal "boiling". As such, you really only "need" (or want) a cup or two of water for many dishes (although I've used as much as 1/2 of the pressure cooker full of water for some soups).
Eventually the main (lid) seal seems to go on most pressure cookers. When that happens, you really can no longer get up to proper pressure, and therefore you can't use the pressure cooker as a pressure cooker anymore. However, some pressure cooker makers will sell "spare parts" (especially including the seals) for reasonable rates if you ask. For example, I was able to make a jumbo sized ($60+ originally) pressure cooker again functional, for around $10 for a new main seal (instead of having to go out an buy a new pressure cooker)...
Treb can whip out the steam tables and tell us the temperature for sure, huh?
Treb, I would normally be concerned about a "college kid" owning a pressure cooker. I don't know if the fact that you are an engineering student makes me feel better or worse. :-)
Just gotta find my Thermo book for saturated steam skewbe got it right though We'll assume that the steam doesn't accept any more heat once it goes from water to steam (that is, H2O stays on the "right" side of the wet/saturation dome).
Pressure Cooker at 15psi (above sea level) = 250.3F
Pressure cooker at 10psi = 238.5 (Linearly Extrapolated between 15 and 5).
Pressure cooker at 5psi = 227
Here's a fun fact.... At 15psi, steam has 1.3314 BTU/lb*R of Entropy (R being Rankine - the absolute temperature scale for Fahrenheit ). That's right, energy (heat) that can never be recovered bringing our universe one BTU closer to ultimate destruction And just for fun... 1 pound of steam @ 15psi takes up roughly 14 cubic feet!
To be honest, I too am a bit concerned considering I don't know the history of this pressure cooker. Which is why I tested it with the maximum amount of water as possible. Sure, if the thing exploded, there's be hot water -- but there would be less steam (which scares me more). I started at 5 - then 10 and finally 15. What I don't like is that this cooker's design is noisy
Time is the best teacher. Unfortunately it kills all its students.