Pressure Cookers

Pressure cooking is a method of cooking food 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 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.
An early pressure cooker, called a 'steam digester', was invented by Denis Papin, a French physicist, in 1679.
When purchasing your pressure cooker, keep in mind the 6-quart size is the standard for most recipes. Select a cooker with a detachable pressure regulator that can adjust the pressure to low (5 pounds=220 degrees F./100 degrees C.), medium (10 pounds=235 degrees F./115 degrees C.), or high (15 pounds=250 degrees F./120 degrees C.). The higher the pressure, the higher the internal temperature and the less cooking time you will need. The safety valve will automatically vent the steam. Choose a pot with heat-resistant handles, a locking lid that is easy to maneuver, and a heavy bottom of stainless steel construction so you can use the same pot to do preparatory sautéing.