Amazing Gadgets: How Does a Pressure Cooker Cook So Fast?

When potatoes are boiled in a pot, they usually take 30 minutes to cook. But boil them in a pressure cooker and they’ll be ready in less than 10 minutes. Why?

When heat is applied to a pot of water, it begins to turn into steam. Bubbles are formed by steam rising from the bottom to the surface. A temperature of 212 degrees Fahrenheit or 100 degrees Celsius is normally given as the boiling point of water, but this is only correct if cooking at sea level. As you go to a higher elevation, the atmospheric pressure (14.7 psi) drops, causing the boiling point of water to drop as well. Therefore, more cooking time is needed. Once water reaches its boiling point in a container, no matter how much heat you add, it can never get any hotter. It just turns to steam and that’s why potatoes take longer to cook in an open pot.

But a pressure cooker has a sealed lid, so the steam produced when water boils builds up inside. As pressure increases, so does the boiling point of water. Therefore, the cooking temperature is increased, which reduces the cooking time required to cook the food. A typical modern pressure cooker operates at an additional pressure of about 15 psi or about twice atmospheric pressure. So the water inside boils at about 252 degrees Fahrenheit and that is why the food cooks faster.

The pressure cooker has a pot-like base and a domed lid. A rubber gasket between the two provides a pressure-tight seal. In the center of the domed cap is a vent into which a weighted pressure regulator is placed. The weight seals the vent, but is raised to control the steam pressure inside at 15 psi. A gentle rocking of the regulator indicates that the heat source is maintaining proper cooking pressure. Typically, high heat is applied to begin boiling the water inside the pressure cooker and then lowered to maintain the gentle rocking motion. Cook for the time indicated in a recipe or cooking chart. For most items, like potatoes and carrots, the cooking time is about 4-8 minutes.

Due to the high operating pressure and high heat, it is very important to observe some safety precautions. Always add liquid to a pressure cooker to prevent excessive overheating and melting of the bottom of the pot. Always lock the lid in place. Always make sure the cover lock works when heat is applied. Never try to open a lid under pressure. A safety relief plug relieves pressure if the regulator fails to rise.