What It All Boils Down To
Practically speaking, what all that science amounts to is this: In a sealed pressure cooker, the boiling point of water goes up as pressure increases.

At standard atmospheric pressure, the boiling point of water is 212°F. But in a standard American pressure cooker, the pressure reaches 1 atm or 15 psi (pounds per square inch) above standard atmospheric pressure*, or 2 atm, which is typically the maximum pressure limit on most cookers. At 30 psi, the boiling point of water is about 250°F.

*The reading on the gauge for nearly every pressure cooker indicates the pressure above atmospheric pressure. At sea level, atmospheric pressure is about 1 atm, or 15 psi. If a dial reads 15 psi, then that means the pressure inside the sealed chamber is 15 psi above atmospheric 15 psi (30 psi total, referred to as “absolute pressure”). This dial reading is technically referred to as “gauge pressure.”

The higher cooking temperature in a sealed pressure cooker means, in general, faster cooking without burning food. And, because the vessel is sealed, it also limits evaporation of critical volatile flavor and aroma compounds. An added plus: the contents of a pressure cooker go relatively undisturbed, since the liquid never effectively boils.

Using a Pressure Cooker at High Elevation
What about pressure cooking above sea level? You might be aware that general cooking times and temperatures for certain recipes differ in places like Denver, CO, or high up in the Andes. At high altitudes, the atmospheric pressure is lower**. For example, in Denver, the ambient pressure is around 12.2 psi.

** Pressure is lower at higher elevations because most of the air molecules in the atmosphere are held close to the earth’s surface by gravity, which means there are fewer air molecules above a higher altitude surface than there are above a surface at a lower altitude.

In general, a pressure cooker adds pressure above the given atmospheric pressure. That means the force that closes the valve as pressure builds in the chamber includes the force of atmospheric pressure. For example, if the atmospheric pressure in Denver is 12.2 psi, then the absolute pressure of the chamber at full pressure is 27.2 (12.2 psi + 15 psi)—nearly 3 psi less than at sea level. Looking at our trusty ideal gas equation, we know that lowering pressure will lower the temperature in a system. In this case, the boiling point of water in a sealed chamber cooking at high pressure will be 244.8°F, almost 6 degrees lower than the same system at sea level.https://kitchenncooking.com/why-do-pressure-cooker-work-well-in-hig...

Of course, a lower boiling point means slower cooking. What does that mean for you? It means you have to increase cooking time to accommodate lower pressure and lower cooking temperature in order to get the same results. A good rule of thumb is to increase cooking time by about five percent for every 1000 feet above 2000 feet elevation.

Choosing the Right Cooker: A Difference in psi
Here in America, you have a greater choice to make when it comes to pressure cookers: electric or stovetop? There are several advantages and disadvantages to using either design. But the single biggest difference is this: Electric pressure cookers operate at lower pressure (12 psi) than their stovetop counterparts (15 psi). Once again, lower pressure means lower temperature, so cooking times will be longer when using an electric model.

Why would you want to cook at lower pressure, and cook slower? The tradeoff is convenience and safety. Electric pressure cookers build pressure up to 15 psi, but maintain a lower pressure during cooking, removing any need to monitor heat. Just like the Ronco Showtime Rotisserie 4000, you can just “set it and forget it.”

How to Cool a Pressure Cooker Down
Closeup of the Kuhn Ricon pressure cooker's pressure indicator rod, showing the red bands for high and low pressure on the rod when it's in a raised position.
Rod that's depressed on Kuhn Rikon pressure cooker to release pressure.
There are three main methods for bringing the pressure in a cooker back down: natural release, quick release, and cold water release.

Natural release involves taking the cooker off heat and allowing the temperature to gradually decrease until the spring-loaded lock disengages. Keep in mind that there could be significant carryover cooking with a natural release technique, depending on how much food you’re cooking.

Quick release, as the name implies, involves removing the weighted jiggler or pressing a button to allow steam inside the cooker to escape. Doing so allows you to stop the cooking immediately, but it also means that the contents of the pressure cooker will boil vigorously. Kenji takes advantage of that boiling to effectively blend his pressure cooker split pea soup without using a blender.

Lastly, there’s the cold water release, which requires running the entire apparatus under cold running water until the cooker depressurizes and the lock disengages. Like the quick release method, the cold water release allows you to access your food effectively immediately. On the other hand, this method doesn’t cause the contents to vigorously boil, which might be desirable for a given recipe. Be aware that the cold water release can’t be used on electric models.

Pressure Power
As the writer Andrew Smith once said, “People fear what they don’t understand (and anything that might blow up in their faces)."*** Hopefully this article has convinced you a pressure cooker won’t blow up in your face, and given you some useful information about how they operate and why they deserve a place in your kitchen.

When you get right down to it, using a modern pressure cooker is about as safe as boiling a pot of water. And when used with care and attention, they can elevate your cooking to greater and tastier heights. But that’s best left for another article, so stay tuned.