Pressure cooking is the process of cooking food, using water or other cooking liquid, in a sealed vessel—known as a pressure cooker, which does not permit air or liquids to escape below a pre-set pressure. Pressure cookers are used for cooking food quicker than conventional cooking methods, which also saves energy.
Pressure cookers heat food quickly because the internal steam pressure from the boiling liquid causes saturated steam (or “wet steam”) to bombard and permeate the food. Thus, higher temperature water vapour (i.e., increased energy), which transfers heat more rapidly compared to dry air, cooks food very quickly.
Pressure cooking allows food to be cooked with greater humidity and higher temperatures than possible with conventional boiling or steaming methods. In an ordinary non-pressurised cooking vessel, the boiling point of water is 100°C (212°F) at standard pressure; the temperature of food is limited by the boiling point of water because excess heat causes boiling water to vaporize into steam. In a sealed pressure cooker, the boiling point of water increases as the pressure rises, resulting in superheated water. At a pressure of 15 psi (pounds per square inch) above the existing atmospheric pressure, water in a pressure cooker can reach a temperature of up to 121°C (250°F), depending on altitude.
Pressure is created initially by boiling a liquid such as water or broth inside the closed pressure cooker. The trapped steam increases the internal pressure and temperature. After use, the pressure is slowly released so that the vessel can be safely opened.
Pressure cooking can be used to quickly simulate the effects of long braising or simmering.
Almost any food which can be cooked in steam or water-based liquids can be cooked in a pressure cooker.