Pressure cooking

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"Pressure cooker" redirects here. For other uses, see Pressure cooker (disambiguation).

Pressure cooking is a method of cooking in a sealed vessel that does not permit air or liquids to escape below a preset pressure. Because water's boiling point increases as the pressure increases, the pressure built up inside the cooker allows the liquid in the pot to rise to a temperature higher than 100 °C (212 °F) before boiling. Most pressure cookers have an internal pressure setting of 15 psi, the standard determined by the USDA in 1917. At this pressure water boils at 125 °C (257 °F). The higher temperature causes the food to cook faster. Cooking times can be reduced by a factor of three or four. For example, shredded cabbage is cooked in one minute, fresh green beans take about five, small to medium-sized potatoes (up to 200 g) may be ready in five minutes or so and a whole chicken takes no more than twenty-five minutes. It is often used to simulate the effects of long braising or simmering in shorter periods of time.

A regulator releases steam when the pressure exceeds the designed pressure for the cooker; usually this takes the form of a weighted stopper commonly called the rocker. This weighted stopper is lifted by the steam pressure, allowing excess pressure to escape. There is usually a backup pressure release mechanism (a safety valve of sorts) that may employ a number of different techniques to release pressure quickly if primary pressure release mechanism fails (for example, if food jams the steam discharge path). One such method is in the form of a hole in the lid blocked by a plug of low melting-point alloy. If internal temperature (and hence pressure) gets too high, the metal plug will melt, resulting in a release of the pressure. Another takes the form of a rubber grommet with a metal insert in the center. At a sufficiently high pressure, the grommet will distort and blow out of its mounting hole, rapidly releasing the pressure.

An early pressure cooker, called a steam digester, was invented by Denis Papin, a French physicist, in 1679.

Larger volume pressure cookers are often referred as pressure canners.

A pressure cooker is often used by mountain climbers to compensate for the low atmospheric pressure at a very high altitude. Without it, water boils off before reaching 100 °C, leaving the food improperly cooked, as described in Charles Darwin's Voyage of the Beagle:

At the place where we slept water necessarily boiled, from the diminished pressure of the atmosphere, at a lower temperature than it does in a less lofty country; the case being the converse of that of a Papin's digester. Hence the potatoes, after remaining for some hours in the boiling water, were nearly as hard as ever. The pot was left on the fire all night, and next morning it was boiled again, but yet the potatoes were not cooked. I found out this, by overhearing my two companions discussing the cause, they had come to the simple conclusion, "that the cursed pot [which was a new one] did not choose to boil potatoes."

A larger scale version of a pressure cooker, used by laboratories and hospitals to sterilise biological waste materials, surgical instruments etc. is known as an autoclave.

Pressure cookers have a reputation as a dangerous method of cooking with the risk of explosion. Early pressure cookers equipped with only a primary safety valve were at risk of explosion if poorly maintained, allowing food residues to contaminate the release valve. Modern pressure cookers typically have two or three independent safety mechanisms, as well as some additional safety features required for UL approval (such as an interlock to prevent opening the lid while pressure exists).

They are referred in the food industry as retorts.