Industry News

How Pressure Cookers Actually Work

2022-08-02

Say the words “pressure cooker” to someone who’s never used one, and they’ll probably think “danger.” It isn’t hard to imagine what’s going through their heads—visions of flying lids, exploding kettles, or much, much worse. Even people who have used a pressure cooker will sometimes get a little leery around one.

But while such hazards may have been possible in the past, they’re practically fiction today. Pressure cookers are safe to use. More than that, they’re incredibly useful. In this age of speed, efficiency, and optimization, there are few tools in the kitchen more suited to cooks who demand good food quickly. If you’re on the fence about buying a pressure cooker—or if you’re an especially obstinate hater, this article is for you.

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.

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.