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High Altitude Pressure Cooking and Stock Making


High Altitude Pressure Cooking and Stock Making

(by Robert Jueneman, October 19, 2011)


Modernist Cuisine says that the optimum pressure (really, temperature) for making stock is obtained at 1 bar or 15 psi.  But that is relative to a sea level ambient pressure.  To obtain the same temperature at my altitude (7000 ft., or 2133 m), I would need to run at 18.5 psi (an additional 0.5 psi per 1000 ft.), and no conventional pressure cooker with jiggle weights or spring settings is capable of doing that, at least that I am aware of.

So following a suggestion by Douglas Baldwin, I bought the non-electric version (1925X) of the 27 liter All-American Sterilizer made by Wisconsin Aluminum Foundry, which is widely used by dentists, tattoo artists, and first aid stations for sterilizing instruments and dressings.  Around the house, we call it “R2D2,” for obvious reasons.

Fortunately, it was just the right size to hold my All-Clad 7qt Pasta Pentola pot, so I could cook stock in a stainless steel pot, instead of using the aluminum container.

But controlling the heat/pressure with my gas stove was a bit of a nuisance, and it required too much constant monitoring when I was making some oxtail consommé and trying to get some work done at the same time.  (I should note that the manufacturer doesn’t recommend using them on glass or ceramic flattop stoves, as the weight might be too much and cause the glass to crack.  And because they are aluminum, they can’t be used on an induction hob.)

So the obvious thing to do was to adapt it to PID control, using one of my heavy-duty Sous Vide Magic controllers.

I looked around for a hot plate that was big enough to heat up a lobster pot, but I didn't find anything affordable.  But hiding in a bottom drawer, unused, was a large electric griddle made by Oster, which was both big enough and strong enough to hold the sterilizer.  And the griddle goes up to 400F, so there was plenty of heat output.  Problem solved. 

So the next task was to modify the unit to get some of the Sous Vide Magic (SVM) probes inside it.  I ordered two 1 m probes from Fresh Meals Solutions, and bought a 1/8" NPT T-adapter and a couple of couplers of the right size to fit the pressure relief valve.  At the same time, I removed the air-relief hose that goes inside the aluminum sterilization pan in order to assure that all of the air is replaced by steam, since I wouldn't be using the pan and I didn’t want the hose to fall into the water.

The two probes (one for the water/steam, and one to measure the temperature of the stock) just barely fit through the T-adapter and couplers.  If I had it to do over again, I would cut the plugs off of the sensors, and try to fish the sensor wires though the side of the T, rather than through the top, and then solder them back on, but I didn't think of that in time.  So the pressure valve sticks out sideways. Oh, well — it works.

In order to make the probes pressure proof, I drilled a hole in a brass cap for the T-adapter coupling, fished the sensors through it, and then applied some epoxy to seal it.  The first epoxy I used was some high temperature metal sealing stuff, but it was almost impossible to get out of the tube, and I didn't think it would be steam tight.  I later put some J-B Weld epoxy on it, with decent but not perfect results -- there was a little steam leakage.  So I put on some more, and that helped, but it still wasn't perfect, although it was good enough to get up to 20 psi.  One final application covered everything nicely, and prevented any steam leakage.

The first couple of times I tried the unit there was some steam leakage from the metal-to-metal seal.  The solution was to wipe the lip of the container with some olive oil to act as a lubricant, and then be careful to make sure the lid is parallel to the base before tightening the knobs.

I heated the sterilizer with about 4 cm depth of distilled water in it on the gas stove until steam started coming out, and then moved it over to the griddle, and turned on the SVM to monitor the temperature.  Even though I was using the new heavy-duty 1500D, I didn't want to
stress the unit too much, and I wasn't sure just how many watts the griddle would draw if I heated it from room temperature using the SVM.

Once the griddle came up to temperature, I could adjust the SVM set point.  I finally determined that 120.0°C was the magic setting for my purpose, and it then held at 18.5 psi for 30 minutes.  If you are at a different altitude, you will need a different temperature.  Within about five minutes from the water probe coming up the temperature, the second probe that was immersed in a measuring cup full of water had come up to about 119°C, so that worked very nicely.

So far, I’ve tried making oxtail consommé, and more recently the potato consommé adaptation of Modernist Cuisine’s Autoclaved Onion Soup, which calls for cooking it at 130°C /265°F for 20 minutes, or at 1 bar/15 psi for 40 minutes.
Nothing ventured, nothing gained, so I thought I would increase the temperature as far as I could, just to see what would happen.  I was able to run it up to 125°C, where it reached about half way into the red band, at around 25 psi, before the pressure relief valve started to gently release steam, so I couldn’t go any higher.  I could of course remove the pressure relief valve entirely, and cap the unit, but that might be just a little too dangerous.

As time permits, I will put the unit through auto-tune in this environment, and see what kind of overshoot I get and how to minimize it, particularly as the water turns into steam.  But for now, this is working very well, and I'm very happy. 

Now, where I am going to store R2D2 when it's not in use?  Why, on the counter in the laundry room, right next to the liquid nitrogen Dewar, and over the cabinet with all of the containers of hydrocolloids, methylcellulose, etc., of course!


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