posted by Dave Arnold
This is our second post on the benefits and pitfalls of pressure cooking stocks. See the first post here.
We recently bought a fancy new pressure cooker
A Brief Recap
The right pressure cookers
It seems like pressure cooked stock should always beat traditional stock because:
- There isn’t much turbulence inside a pressure cooker, so cloudiness is reduced.
- Higher extraction temperatures extract flavor more completely.
- Higher temperatures encourage more delicious “high temp flavors,” such as the meaty flavors caused by increased protein breakdown.
- The sealed pressure cooker should preserve volatiles.
Why venting pressure cookers underperform is still a mystery to me. But they always do.
A Note on our New Pressure Cooker
The Wisconsin Aluminum Foundry Company (WAFCO) has been making the “All American” line of pressure canners since 1930. Their pressure canners are made entirely of aluminum and are usually big (up to 41 quarts). Pressure canners are designed primarily to sterilize jars and cans for home canning—not to cook in. The standard pressure canner regulates pressure with an adjustible weight, so once working pressure is reached, it vents steam—bad. You can make the weight heavier and use the very nice and accurate gauge to regulate pressure up to about 18 or 19 psi without venting, but to really go high-pressure you want a pressure sterilizer. Pressure sterilizers are used by dentists and tattoo artists; they are basically inexpensive autoclaves. Our WAFCO canner converts to a sterilizer just by changing out the lid. We have the 25 quart stovetop model.
The pressure sterilizer will not vent steam unless you release the valve or take the unit above 24.5 psi. It is dead quiet. A regular pressure cooker at 15 psi reaches 250° F (121° C). My pressure sterilizer running at 24.5 psi reaches 266° F (130 ° C).
The 25 quart pot heats rather slowly, and it takes a while to get the hang of regulating pressure by adjusting the gas—I plan to build a temperature regulator soon. Be careful with the sterilizer. It has a tube on the bottom of the lid. If that tube goes under the surface of your cooking liquid, the vent valve will spray hot liquid when opened. In these tests we cooked our food in stainless bains that we put inside the pressure sterilizer.
One quirky feature of these pots: they have a metal-on-metal seal, with no rubber gasket.
Test Number 1, Changing Pressures
We ran this test on previously prepared stocks so we could eliminate ingredient variables. The tests discussed in our first pressure post indicate that pressure cooking a previously prepared stock produces similar results to creating a stock entirely in the pressure cooker. We treated white chicken stock and brown veal stock in five different ways, as follows:
- Heat briefly on the stove (control 1).
- Pressure cook in a venting pressure cooker at 15 psi for 30 minutes (control 2).
- Pressure cook at 15 psi for 30 minutes.
- Pressure cook at 20 psi for 30 minutes.
- Pressure cook at 24 psi for 30 minutes.
You can see that higher pressures = browner color. Chicken and veal stocks reacted similarly at the same pressures, so I’ll discuss them together. Confirming our previous results, stovetop was better than 15 psi vented, but not as good as 15 psi. The aroma of 15 psi vented was superior to both stovetop and 15 psi unvented—bizzare. 20 psi had a good aroma, some thought better than 15 psi unvented, but its taste was muted. The 24 psi stock was the brownest by far, but smelled and tasted dead. We need to run tests between 0 and 15 psi to determine optimum pressure.
Result: 15 psi non-vented chicken and veal stocks were the winners.
Test Number 2, Adding Lye:
This one gets a little weird. Friend of the blog and pro-chemist Schinderhannes suggested that we try to increase the meaty flavor of stocks by disrupting the proteins with a strong base (like sodium hydroxide, also known as lye), pressure cooking them, and neutralizing the base with a strong acid (like hydrochloric acid). Don’t get freaked out, we aren’t serving this to people—it was just a test.
There’s something very appealing about Shinderhannes’ proposal. Lye ( NaOH) + Hydrochloric acid (HCl) combine to make water and table salt (H2O and NaCl). The trick to not poisoning people is neutralizing the lye.
We don’t have access to high grade lye, so we used this:
Don’t use this stuff. I don’t want to hear about you getting hurt. Eating only a small crystal will do severe, irreparable damage to your insides. My doctor mom used to tell me horror stories of kids who came into the ER after eating drain cleaner. Anyway, we prepared two identical batches of chicken meat and water, added some 33% lye solution to one (we added 0.5% by weight NaOH to the stock), and pressure cooked them both for 45 minutes in a non-venting pressure cooker at 15 psi. Here is what they looked like:
The difference is pretty plain. The lye stock is still poisonous at this point so we need to add hydrochloric acid to neutralize it. Problem is, I can’t get pure hydrochloric acid, so I went to the hardware store for muriatic acid, which is fairly concentrated HCl, used to clean tiles. We added enough HCl to get a neutral reading on our pH meter. Look what happened:
Whoa! The stock turned white and clouded up. I tasted it to make sure it wasn’t poison. It wasn’t. Then we figured out how much salt to add to the normal stock to match the salt created in the lye stock acid base reaction.
Here is Nastassia tasting them blind.
Well, the normal stock won. The lye stock tasted a little weird. The next day the lye stock looked even stranger:
The stock on day 2 smelled and tasted strongly of lye. I’m guessing the lye was trapped in the precipitate that formed when we added the acid, and it leached out overnight. The lye taste was still present after we got rid of the cloudy stuff in our centrifuge.
All in all, not a ready-for-prime-time technique, but a fun experiment.