 Pressure cooking is a method of
cooking in which the boiling temperature of water is increased using a
special vessel, causing 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.
This is accomplished using a pressure
cooker, a sealed vessel that does not permit steam to escape until a
preset pressure is achieved. 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. 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. However, it is best
not to rely on this feature.
A pressure cooker can be used at high
altitude to compensate for lower atmospheric pressure. Without it, water
boils off before reaching 100 °C, lengthening the cooking time for
recipes.
In some countries, the microwave
has replaced the pressure cooker as a technical fix for faster cooking.
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