Science Fair Project Encyclopedia 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. 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