How Do Pressure Cookers Work?

History, Mechanisms, and Advantages of Pressure Cookers

Pressure Cooker
Pressure Cooker Julie Magro/Flickr/CC 2.0

Pressure cookers are a convenient kitchen appliance used to cook food quickly with the power of steam pressure. Even without pressure steam conducts heat and cooks faster than dry air, but with increased pressure, the steam can rise above its usual maximum temperature and cook even faster. These factors make steam pressure cooking faster than baking, steaming, or boiling.

Pressure Cooker History

The first pressure cooker was designed by Denis Papin, a French physicist. He called this cooker the "steam digester" and presented the invention to the Royal Society of London in 1681, where it earned him membership into the society. The first patent for a pressure cooker was granted to Georg Gutbrod in Spain in 1919, but it wasn't until Alfred Vischler presented his pressure cooker at the 1938 World's Fair that commercial production began for home use. Since this time pressure cookers have been prized for their time and energy-saving qualities.

Steam—an Excellent Heat Conductor

Boiling and steaming are already great cooking methods because water is a much better conductor of heat than air. To demonstrate this, think about how you can easily place your hand in a 200 F oven without it burning, but if you were to place your hand in a pot of boiling water (212 F), you would burn immediately. This is because water (or steam) conducts energy (heat) very well, whereas air does not. The limiting factor of cooking with water or steam is the maximum temperature.

Maximum Boiling Point of Water

Water boils at 212 F, at which point it turns into steam. Once the water reaches 212 F and begins to boil, the temperature does not increase any further until all of the water has been converted to steam. The boiling water and steam remain at 212 F, regardless of how long it boils, limiting the rate at which it can cook food.

Just Add Pressure So Water Boils at Higher Temperature

The only way to increase the temperature of boiling water as it converts to steam is to increase the surrounding pressure. This can be achieved by trapping the steam in an enclosed space. As water transforms into steam, it expands in volume. If the volume is not allowed to increase, the pressure (and therefore temperature), will increase. Pressure cookers trap steam in an enclosed space through an air-tight, locking lid. The longer the water boils, the more the steam pressure builds within the vessel.

Three Advantages in One Cooker

Pressure cookers have three advantages over oven cooking, the high heat conductivity of steam, the increased temperature from steam pressure, and high energy efficiency.

  • The conductivity and increased temperature can cut cooking times to a fraction of their oven or stovetop counterparts.
  • The shortened cooking time and contained cooking environment greatly reduce the amount of energy needed to cook food, especially those that usually require long cooking times (beans, roasts, rice, and more).

Pressure cookers are a great addition to any kitchen and can make cooking fast, easy, and affordable.