Pressure cooking

:Pressure cooker redirects here. For the 1997 movie, see Pressurecooker.

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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. 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.

Related Topics:
Boiling point - Pressure - Braising - Simmering

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A safety valve releases steam when the pressure exceeds the safety limit for the cooker; usually the steam pressure lifts a weighted stopper allowing excess pressure to escape. There is usually a backup pressure release mechanism, 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.

Related Topics:
Safety valve - Steam

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

Related Topics:
Denis Papin - 1679

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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:

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At the place where we slept water necessarily boiled, from

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the diminished pressure of the atmosphere, at a lower

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temperature than it does in a less lofty country; the case being

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the converse of that of a Papin's digester. Hence the potatoes,

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after remaining for some hours in the boiling water,

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were nearly as hard as ever. The pot was left on the fire

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all night, and next morning it was boiled again, but yet the

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potatoes were not cooked. I found out this, by overhearing

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my two companions discussing the cause, they had come

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to the simple conclusion, "that the cursed pot [which was a

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new one] did not choose to boil potatoes."

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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.

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