Cookbook:Pressure Cooking

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, a rubber seal and pin, or a rubber ring seal. If internal temperature (and hence pressure) gets too high, the release mechanism will trigger, 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, but cannot perform the same task that programmable electronic pressure cookers, also known as multicookers as delayed cooking and other features.

Water And Periods of Time
Usually, you need 1 part of product (beans, chickpeas...) and 3 of water for cooking ( excepting rice that is 1,8).

On the other hand, with pressure cooker you do not need pre-soaking.