Hacking a better pressure cooker

This pressure cooker hack on [Dave Arnold]‘s great cooking blog was sent into us (thanks, [techartisan]!). Most pressure cooker recipes are written for pressure cookers that can go up to 15 PSI or 250° F / 121° C. At these temperatures, a lot of interesting chemistry happens in the food. The popular Cuisinart electric pressure cooker doesn’t reach these pressures and temperatures, so [Dave Arnold] set out to make his Cuisinart better.

After measuring the temperature with a thermocouple, [Dave] deduced that the Cuisinart cooker only reached 237° F and 9 PSI. After having a look at the electronics, he realized that adding a resistor to the temperature sensor circuit would give him the pressure he wanted. After soldering in a trim pot, everything went swimmingly and the cooker was able to reach 15 PSI.

[Dave] isn’t sure how his modifications will hold up – he doesn’t know how the cooker will hold up to overheating (and there are a few concerns about non-stick pressure cookers in the first place). That being said, it’s a great mod to get some more capabilities out of a Cuisinart.

Comments

  1. Willaim says:

    I like a good hack as much as the next guy but I really have to question how wise it is to hack a pressure vessel that is under high heat and pressure??
    Before even worrying about teflon coatings (Im pretty sure they stay stable and intact up to 400 degrees and possibly higher) I would worry about the extra 13 degrees and especially the extra 6lbs of pressure on the release valve.
    When the emergency pressure release valve goes in this thing its going to spew 250 degree food and liquid all over the place I would definitely keep my face away from the top

    • Philippe says:

      This hack doesn’t seem very safe to me either.
      I have a vision of sizzling hot food flying all over the kitchen.

    • Rick says:

      Did it occur to you that the release valve is not in the food mixture and actually is above in the air? So if it opened, it would just release a little steam and only enough to lower the pressure below the closing point of the valve.

      They actually post a hack and all you chumps whine about “safety” when you don’t actually understand the situation at all. Ugh. Middle schoolers shouldn’t be allowed summer breaks.

      • willaim says:

        Did i ever say not to do it? (I even called it a good hack) Just said keep your face away and did it ever occur to you that as the pressure is relesed quickly the liquid inside rapidly boils causing turbelence that tends to push food out the opening at high velocity? Ever seen the pressure release on one of these go i have and i found bits of ham potatoes and green beans everywhere. Not to mention the chunk of metal that is the pressure release valve put a good dent in my fume hood so thanks for your comment but just bc you read it in his blog doesnt mean the unexpected never happens…

    • willaim says:

      By all means dont take this hack down but caution should be taken yes he said do at your own risk in his blog but it still needs to be said…. Back in the 90’s we were using banks of high capacity caps like 10-12 fared worth hooked together with brass bars and we decided to drop a ball bearing on it to see if it would take off wll it sure as hell did tore a hole through the roof on its way out the first thing i did was make sure my face was still intact and every time i told someone about our findings i was sure to give the warning…. Hey just looking out for peoples well being…. And faces

  2. henry says:

    The specs are probably limited to 9 psi for a reason, might be because its not designed to withstand 15 psi.

    Trust me, pressurised boiling hot stew in your face is not nice, i found out the hard way when someone decided to cook a can on a fire without piercing a hole

  3. LeJupp says:

    Technically, by the time it reaches your face, it’s only hot stew. Don’t know if that makes the experience any more desirable though…

  4. Truth says:

    I always think bomb for some reason when ever anything involving pressure is forced outside it’s design specification. But the thing still has a working mass based pressure release valve so it should still fail safe, I think, maybe. Well even if it does not properly fail safe it should turn into more of a ball shape with steam shooting out of it before it blows.

  5. Jaycee says:

    “it’s a great mod to get some more capabilities out of a Cuisinart”

    Being run at nearly double its rated pressure,
    there’s a serious risk it will fail catastrophically.

  6. You know, with the old low-tech version you could just put a little heavier weight on the vent and you were done. No soldering. No worries about the thick metal walls being able to handle the pressure.

  7. Strangerover says:

    Pardon my ignorance. Isn’t 15psi just barely more than atmospheric pressure (about 14psi)? Are these pressures measured with atmospheric pressure as the de facto zero-point?

    • blacketj says:

      Yes it is using atmospheric as the zero point. It is called gauge pressure. It is the difference between the outside pressure (atmospheric in this case), and the internal pressure.

    • Philippe says:

      You’re absolutely right.

      I think they’re talking about the delta psi, or the pressure differential : 15 psi on top of the atmospheric pressure. Basically you would have 30 pounds pushing inside and 15 pushing from the outside on every square inch of metal.

      See http://en.wikipedia.org/wiki/Pressure_cooking

      Excerpt: “Most pressure cookers have a working pressure setting of 15 psi (approx. 107 kPa) over the existing atmospheric pressure, the standard determined by the United States Department of Agriculture in 1917. At this pressure boost relative to sea-level atmospheric pressure, water boils at 122 °C (252 °F) (refer to vapor pressure of water).”

  8. ColinB says:

    I assume that the 15 psi means “psig” (gauge pressure, relative to the surrounding atmosphere) rather than “psia” (absolute pressure). Everyday air pressures are usually measured in psig: tire pressure, etc.

  9. ColinB says:

    P.S. We have a new contender for the 2011 Darwin Award!!

  10. RexOfRome says:

    Under the new rules the above comments are unacceptable. You guys are too negative. Just tell him he did a great job and move along.

    • macona says:

      No, you can be negative, you just cant be an ass about it.

    • jeff says:

      @rexofrome

      i have lot’s of respect for anyone trying new things and breaking/making stuff.

      and for me, having respect is telling things the way they are. if one of my friend is doing a stupid dangerous thing i will tell him.
      i personally know 3 cases where blind positivism led to death. “great idea!”, “good job nice work!”

      you know a safety officer has to CONFRONT others that think their methods are safe. it’s not out of lack of respect, it’s for concern and well being of others.

      risks and limitations ARE FACTS, NOT PERSONAL OPINIONS.

    • N0LKK says:

      Have to certain the new guidelines do not require yo say a good job if we believe it’s not, no doubt they require criticism to be civil. I agree some of the comments here where personal attacks, however the HAD staff allowed them to remain. Howsoever they moderate is gain, or their loss,the small stuff I’m not going to sweat.

  11. chic says:

    My own pressure cooker was sold as a “low pressure cooker” (10psi istr). The point being that I can cook for say 15 minutes, then open it to add something or remove something, without waiting for a lengthy de-pressure phase. then go straight back up to pressure in a few seconds. I wonder if this person is actually overstressing a lp pressure cooker…

  12. Chris says:

    Good article. Didn’t know I was going to be getting an education on pressure cookers this morning. :) Never heard of Hamine eggs before and my curiosity (and appetite) is whetted.

    I’d think the pressure valve would release long before there’s any risk of damage to the pressure vessel. But there’s one other risk. There could be some plastic parts in the base that might be damaged by the higher temperatures. Might be worth taking a peek at the innards from time to time to make sure all is well.

  13. Pete says:

    Regarding safety, what if you had a larger pressure chamber to put the electric pressure cooker into? That way the total pressure inside the pressure cooker would be delta P plus local (larger pressure chamber) atmosphere, but the pressure differential on the electric pressure cooker itself would remain within design specs.

  14. Kt says:

    Cool hack,
    Worst case scenario the thing melts or catches on fire (not a problem as long as you’re around and have an extinguisher).

    Other possibility is that the emergency pressure plug blows and pokes your eye out (probably only an issue on the older 1970’s style pressure cookers, I think the newer ones aren’t as much of a hazard.)

    This is a modern pressure cooker, I’d be shocked if it didn’t have an emergency pressure release SOMEWHERE.
    It most likely will not blow up.

  15. ScottInNH says:

    @LeJupp says:

    “Technically, by the time it reaches your face, it’s only hot stew.”

    Um, no, you are dangerously wrong.
    With a pressure cooker, you have water which is super-heated past boiling point.

    With pure water in the cooker, you will have third degree burns in an instant.

    Any cook can tell you about gravy and sauce burns. If you were cooking something thicker – like gravy – you will be hit with something that is BOTH having a higher thermal mass, and adhesiveness. Much more heat will be transferred into the skin.

    … and this is only for a scenario of the emergency pressure valve RELEASE. I assume this product has a safety valve to prevent any rupture. But if a pressure release valve failed you might end up with a containment breach, and then airborne hot food is the least of your worries.

  16. lwatcdr says:

    I wouldn’t worry too much about a kaboom. I am sure they have both a mechanical and electronic pressure cut offs. I would also bet that they test well past 100% of rated pressure. Simple reason is that all of that is cheaper than a court case.

    • Hackerspacer says:

      It *HAD* (maybe) an electric cutoff. It no longer does. The only thing stopping a kaboom is the manual pressure release.

      • lwatcdr says:

        He hacked the thermostat not a pressure sensor. In fact he didn’t see one. Yes there is a mechanical safety valve. So I still wouldn’t worry too much about an earth shattering kaboom.

    • Hackerspacer says:

      9 to 15 PSI is a change of 6 PSI. I would estimate this vessel to be about a foot in diameter and one foot tall. Taking the surface area of this cylinder in inches, you get pi * r^2 * h. Or 3.14 * 6^2 * 1. Which gives you 113.04.

      Multiply that by 6 and you have 678.24 additional pounds of force being applied equally to the walls of this vessel. It now has 1,695.6 PSI applied to it, up from 1,017.36.

      In a perfect world, a pressure vessel stated to be rated at 1000 PSI should in no way catastrophically fail if 1700 PSI were inadvertently applied to it – the pressure relief should kick in at around 10 PSI or so. Disallowing that to take place. Removing or disabling that is a recipe for disaster. This isn’t even a remotely safe hack and is a very bad idea. Buy a proper pressure cooker.

      • Hackerspacer says:

        Sorry, not 1700 and 1000 PSI, I meant 1700 and 1000 lbs of force.

      • lwatcdr says:

        A. He didn’t modify the relief valve.
        B. This is a proper pressure cooker.
        C. He did modify the thermostate.
        D. He did have a warning.

        Did no one read his blog? If they had they should have seen the mind numbingly scary and stupid thing that he says he did do.
        “Pushing pressures to an extreme, I’ve sealed potatoes in a pipe and thrown them in my deep-fryer set at 365 F, generating 148 psi. Wow, did those potatoes taste bad. Brown all the way through and gross. Possibly the worst stuff ever (see here).”
        That is a pipe bomb in hot oil! YIKES.

  17. SuperNuRd says:

    @RexOfRome We say these things out of concern not of disqust.

  18. JohnConnor says:

    Agree with ColinB.

    This “hack” is a ticket to a great Darwin Award.

    Has anyone considered the thermal cycling of the material the cooker is made out of (at double it’s rated design limit) ?

    Ever hear of “stress fractures” ?

  19. Probably a really dumb idea, but has anyone considered *negative* pressure cooking?

    e.g. take chamber down to 25% atmospheric and heat up to 65C. Water will then boil BUT due to the lower pressure less damage will be done to the food.

    Pressure cooker sous vide anyone?

    :-)

  20. DainBramage1991 says:

    Good hack, but… My biggest concern would be counting on only one failure-prone mechanical safety valve.
    Somehow I think it would be a better idea to just fork out the money for a higher pressure cooker.

  21. lemon says:

    Just as a little exercise in pressure vessels, check what it would take to make this gauge of steel/aluminum rupture. (hint: quite a bit more than 15 psi)

    and don’t use hackerspacer’s calc, it isn’t the correct method.

    • Hackerspacer says:

      I took the surface area of the internals and multiplied that in inches by the PSI. What is incorrect about that?

      • N0LKK says:

        Best to ignore a comment that says something is wrong , but doesn’t offer the correct way. Yes your method is correct. However the weakest surface in kind of vessels is the ends, the reason they are generally domed. the force being applied to end is the force being applied the appliances lid lock. The walls of suck a vessel are the strongest surface.

      • Luke says:

        No, the calculation is wrong. What’s with the “h” = 1?

        If you want to calculate the axial load in the walls of the cylinder, then calculate the force on the ends (area of cap times pressure). Ignoring your “h” value, this means the axial load in the walls has increased by over 600 lbs. Now calculate the stress by determining the wall area (thickness of wall times circumference).

        To calculate the tangential load or stress in the walls, then take the area of the cross section (height of cylinder times diameter) and multiply by the pressure. If the height is 5 inches, then the area is 12×5 or 60 sq in. This times the pressure is 360 lb. The total area of the wall is twice the thickness times the height. Divide into 360 for the stress. To calculate the total peak stress, you have to take the vector addition of the axial and tangential stresses. BTW – twice the thickness comes from the fact that the both sides of the cross section of the pressure vessel carry the load.

      • Luke says:

        BTW – these calcs I did are for the increase in pressure, not the total. Hence the use of only 6 psi.

    • Hackerspacer says:

      When you take foods up to 100,000 PSI or so at room temperature, you can kill bacteria. Not very food takes kindly to this (squishy things like strawberries don’t) but most do (meat, most vegetables, etc).

      Not sure how well that would apply to killing prions or spores but since heat “scrambles” DNA in a similar way but this is done at room temperature…. it effectively sterilizes food without heat and without radiation.

      Now the trick is getting the food up to 100,000 PSI safely :)

  22. Bubba Gump says:

    Hmm…Underwriter’s Laboratories, UL136, covers pressure cookers. Not only electric pressure cookers, ones that are put on gas burners. Do ya think there is a reason for safety standards? You betcha…

    Normal pressure cookers are also not to be used for frying. Specialized pressure fryers (like those at KFC) are used.

    I think he should take his hack AND pressure fry some chicken…

  23. Matt says:

    Superheated steam is dangerous stuff. Even if the relief valve blows (rather than some other part breaking open), you will probably get serious burns if your hand is over it at the time, if is anything like the safety valve in my pressure cooker. It’s a rubber plug in the lid that will blow out if the pressure is too high.

  24. Techartisan says:

    I used to use a modified pressure cooker as a pressure chamber for liquid plastic molding. Id remove the pressure release valve…drill the top and use fittings to couple the pots lid to my compressor.
    Around 50-60 psi most pressure cookers will rupture their rubber seal. Granted I wasnt raising the pressure through heat….but the principle is the same….I now use paint pressure pots at around 80psi simply due to their larger capacity per dollar expense….

    The dental lab I work in uses a pressure pot thats manufacturer markings indicate it was originally a pressure cooker….though it is sold modified much the way Ive described as a “Pressure Pot” by a major dental manufacturer.

    what he has done in his hack is merely modify an underperforming appliance….YOU NEED 15psi to properly pressure cook.

    I actually submitted this article for review having found the NONhack nature of the site and quality of the writeup GREAT.

    Given todays wealth of “electrocute yourself for fun” articles Im amazed at the comments this article has drawn.

  25. N0LKK says:

    Wow!I did see the actual item in the photos, or read anything about the use of a proper pressure gauge for the testing. Because there’s no way to predict the failure mode, it’s impossible to predict the damage that may happen, if a failure occurs. I wonder if Cuisinart learns of the hack if they will send the dude appliances again?
    Oh well…

    • N0LKK says:

      Big difference in the manufacture make, and test the mods. any that fact is not relative give use the appliance modified in the home shop is the same alliance in your work place. Browser word search only found gauge in the comment, not inn the mod derails. apology to Dave, but because he’s evidently guessing at the pressure. not a good practice. t the event an electric pressure that can attain 15 Psi, it make more sense the mod the appliance that is rated for 15psi to use electric power. In Dave does seem to have the skill to do that

  26. JamieWho says:

    Wow, I love that any hack that could remotely become a safety hazard gets 20-30 comments immediately.

    If you buy a pressure cooker, it should cook the food under pressure, at the proper pressure. Also, he didn’t actually hack the pressure that the unit cooks at (not directly). He only increased the temperature cutoff so that it would cook food at 249F instead of 237F. The pressure was only assumed to be at a correct 15psi.
    Additionally, it is a dual pressure cooker. It has both a high and low pressure mode, so it was designed to be used at the “standard” high pressure.
    Yes, pressure cookers are dangerous. So are PC power supplies and remote controlled lawn mowers. That doesn’t mean they shouldn’t be hacked.

  27. Per Jensen says:

    Great hack.

    Reading about that kind of pressure, i keep thinking of this ;-)

  28. Mike says:

    Not a big fan of whining about “the way things used to be” on a website, but I’ve gotta say it: since HaD exploded in popularity, everybody’s a freaking safety expert. I was on the fence about the “mains patch cable” a while back, but even that was an April Fool’s joke.

    The industry standard is 15 psi for pressure cookers. Just because Cuisinart sold this cooker operating at a lower temperature does not mean it’s rated below this. I have serious doubts that a steel container is going to rupture from 15 PSI. It also has a relief valve. Given this, I have to wonder how many of you actually read the article. He shows in great detail both the pressure indicator and relief valve.

    Regardless of how safe this is or isn’t, I’d think we all come here for the hacking, instead of just trying to pick everything apart. If you want industry-regulated consumer products that are “safer,” then please just go to Wal-Mart instead of coming here to tell everyone how their ideas are unsafe.

    Those of us that know the risks know how to mitigate them; those who don’t, find out quickly.

    Sorry for the long rant, but…come on, people. At least try and pretend you’re not the smartest person in the room for a few seconds.

  29. lentil says:

    ive always wondered if rapid depressurization of food… lets say cheap beef cut… effectively tenderizes… perhaps wouldnt even need heat at all. just put that ‘ole steak in and pump 150psi from your air compressor in there. hold for ten minutes. vent rapidly.. gather with spatula and grill on coals. “guys, guys, the lentils just, like, exploded, man… heeeaaavy”

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