How a pressure cooker works

Everything you need to know about how a pressure cooker works!

Mention the word pressure cooker to someone who’s never used one, and they’ll probably think “danger.” It’s not hard to imagine what’s going through their heads—scenes of flying lids, exploding kettles, or much worse. Even those who have used pressure cookers occasionally One will get some rest around.

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But while such dangers were possible in the past, today they are practically fiction. Pressure cooker is safe to use. More than that, they are incredibly useful. In this age of speed, efficiency and optimization, few tools in the kitchen are perfect for cooks who demand good food fast. If you’re on the fence about buying a pressure cooker—or if you’re particularly monotonous, this discussion is for you.

A detailed history of pressure cooking

The origins of the pressure cooker can be traced back to the 17th century French physicist and mathematician Denis Papin. Papin, who shared notes with such legendary brainiacs as Christian Huygens, Gottfried Leibniz, and Robert Boyle, is best known for his 1679 invention of the “steam digester,” a precursor to both the pressure cooker and the steam engine. Also known as the “Bone Digester” (such a hardcore name!) or “Papin’s Digester”, the device was designed to extract fat and collagen from bones; After extraction, the rendered bones can be turned into bone meal, which can be used as a dietary supplement or fertilizer.

The steam digester consists of a closed vessel with a tight-fitting lid. As the food and water heat up, the vessel traps steam, increasing the internal pressure of the vessel. Papin’s initial design did not include a pressure-relief mechanism, leading to several early explosions. Fortunately, Papin subsequently invented a steam-release valve to prevent such accidents from occurring.

Over the next 200 years, intrepid minds refined the concept. But it wasn’t until the 1930s that the pressure cooker finally entered the home kitchen, with the introduction of Alfred Visser’s “Flex-Seal Speed Cooker” in 1938, and later a model from the National Pressure Cooker

Company (now renamed National Presto Industries and still in the pressure cooker game). In 1939.

Since then, not much has changed, and pressure cooker designs can be categorized by generation. The first and simplest “old type” pressure cookers have a weighted “Ziggler” valve that releases and controls the pressure, making a whooshing sound as steam escapes. Today, most pressure cookers you can find are first-generation designs, with small safety improvements like a pressure-sensitive locking mechanism as well as the ability to adjust pressure by changing the weight of the valve.

Second-generation pressure cookers are quieter, have a hidden, spring-loaded valve, and let you choose at least two different pressure settings by adjusting a dial. Some cookers do not release any steam during cooking; Instead, they have an indicator that displays the pressure level. Overall, second-generation models offer more precision when cooking than first-generation models.

Third generation models are a relatively recent innovation. Unlike the first two generation models, all these models have an electric heat source that maintains the correct pressure while cooking. They usually have a timer and more elaborate models include digital controllers, delayed cooking functions and smart programming to cook specific foods.

What about pressure cooker explosions?


The legend of pressure cookers exploding is not entirely unfounded. As the United States entered World War II, the government promoted self-sufficiency programs, which encouraged the canning of home-grown products. Steel was appropriated for the manufacture of pressure canners, and pressure cookers also grew in popularity. After the war, demand for pressure cookers was at an all-time high, leading to increased production. Manufacturers started pumping pressure cookers, but at the cost of materials, construction and overall safety. For example, 50s models had a single, poorly constructed weighted valve that easily got stuck in debris. The pressure is built to an extreme, the gasket will blow, and water or steam will blow from the top; In some cases, the lid will fly right off.

Fortunately, manufacturing and design practices have improved considerably, and today’s pressure cookers have several fail-safe mechanisms to ensure safety, such as multiple valves, dual pressure regulators, and spring-loaded lid locks. No more sketchy deathtraps. So the current pressure cookers are safe to use.

How a pressure cooker works

A pressure cooker is a sealed chamber that traps the steam generated as its contents are heated. As steam is formed, the pressure increases, exceeding the boiling point of water at 212°F (100°C). In general, this higher temperature shortens cooking time and extracts flavor from food more efficiently, due to lack of evaporation.

The Science Behind Pressure Cookers

Time for a quick high school chemistry refresher: The pressure cooker can best be explained by the “ideal gas law” (or “general gas equation”), which describes the behavior of most gases under most conditions. This is usually given by: PV = nRT

P stands for pressure; V stands for volume; T means temperature; n represents the volume of a given gas (expressed as the number of particles); and R represents a constant (the ideal gas constant, but, for simplicity, let’s say it’s not very important here).

In the closed chamber of the pressure cooker, we can make a few assumptions. For one, the volume of the chamber ( V ) does not change. Second, R (being a constant) does not change. Third, there is a maximum pressure that can reach the chamber, controlled by a valve system. As the pressure cooker heats the food (ie, heats the water in the food), T rises. And as T increases, something else must increase to balance the equation. Since we assume that V is constant, the pressure ( P ) is also likely to increase.

We can also explain this increase in pressure in another way: as the system heats up, more energy is supplied to the water vapor molecules, causing them to bounce around and collide randomly with each other and against the walls of the container. This collision force against the wall is a definition of pressure, based on the “gas kinetic model”.

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But what happens when P maxes out? For a moment, consider a pressure cooker containing water and chicken bones to make stock. As the container reaches maximum pressure, the temperature (T) plateaus. If we continue to supply heat (energy) to the system, we are still supplying energy for more random collisions between water molecules. In the absence of a valve, the water will continue to heat, building pressure indefinitely. But something has to give. In this case, n (volume of gas) decreases. We see it in the form of steam that trips the pressure-regulating valve when cooking our chicken stock. This is the case with first-generation stove-top cookers. For newer, third-generation electric models, the cooker detects both pressure and temperature and regulates the amount of heat delivered by the heating element, so you don’t see too much steam escaping or hear too much noise.

Using a pressure cooker on high heat

What about pressure cooking above sea level? You may be aware that typical cooking times and temperatures for certain recipes are different in Denver, CO, or higher up in the Andes. At higher

altitudes, atmospheric pressure is lower**. For example, in Denver, the ambient pressure is about 12.2 psi.

** Pressure is lower at higher altitudes because most of the air molecules in the atmosphere are closer to the Earth’s surface by gravity, meaning that there are fewer air molecules above a surface at a lower altitude than above a surface at a lower altitude.

In general, a pressure cooker adds pressure above the given atmospheric pressure. This means that the force that closes the valve as pressure builds up in the chamber includes the force of atmospheric pressure. For example, if the atmospheric pressure in Denver is 12.2 psi, the absolute chamber pressure at full pressure is 27.2 (12.2 psi + 15 psi)—about 3 psi less than at sea level. Looking at our trusty ideal gas equation, we know that lowering the pressure will lower the temperature in a system. In this case, the boiling point of water in a sealed chamber cooked under high pressure would be 244.8°F, about 6 degrees lower than the same system at sea level.

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

Choosing the right cooker: a difference in psi

Here in America, you have a big choice when it comes to pressure cookers: electric or stovetop? There are several advantages and disadvantages to using both designs. But the single biggest difference is this: Electric pressure cookers operate at lower pressure (12 psi) than their stovetop counterparts (15 psi). Again, lower pressure means lower temperature, so cooking time will be longer when using an electric model.

Why do you want to cook at low pressure, and cook slowly? The tradeoff is convenience and security. Electric pressure cookers create pressure up to 15 psi, but maintain lower pressure during cooking, eliminating the need for heat monitoring. Like the Ronco Showtime Rotisserie 4000, you can simply “set it and forget it.”

How to cool a pressure cooker

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There are three main methods of pressure relief in cookers: natural release, quick release and cold water release.

A natural release involves turning off the cooker’s heat and allowing the temperature to drop slowly until the spring-loaded lock disengages. Keep in mind that depending on how much food you’re cooking, there may be significant carryover cooking with a natural release technique.

Quick release, as the name suggests, involves removing a weighted jiggler or pressing a button to allow steam to escape inside the cooker. Doing this will stop the cooking immediately, but it means 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.

Finally, there is the cold water release, which requires running the entire appliance 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 immediately and effectively. On the other hand, this method does not allow the contents to boil vigorously, which may be desirable for a given recipe. Be aware that the cold water release cannot be used on electric models.

Also Read: Ultimate Guide to the Best Cookware

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As author Andrew Smith once said, “People fear what they don’t understand (and things that might blow up in their face).”*** Hope this article has convinced you that a pressure cooker won’t blow up in your face, and they will. Here’s some useful information on how they work and why they deserve a place in your kitchen.

When you get 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.

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