From Wikipedia, the free 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.

Pressure cookers may be referred to by several other names. An early pressure cooker, called a steam digester, was invented by Denis Papin, a French physicist, in 1679. Large volume pressure cookers are often referred as pressure canners, due to their capacity to hold jars used in canning. A version of a pressure cooker used by laboratories and hospitals to sterilize materials is known as an autoclave. In the food industry, pressure cookers are often referred to as retorts.

Contents 1 Operation 2 Advantages 3 Safety features 4 Use at high altitudes 5 Use in food detoxification 6 See also 7 References 8 External links

Since pressure cooking depends on the pressure of steam, the process cannot easily be used for methods of cooking that produce fairly little steam, such as roasting, pan-frying or deep-frying. Most pressure cookers sold in the U.S. have an internal pressure setting of 15 psi (1 bar), the standard determined by the USDA in 1917^{[citation needed]}. At this pressure boost relative to sea-level atmospheric pressure, water boils at 125 °C (257 °F). The higher temperature causes the food to cook faster; e.g., cooking times can be reduced by 70 percent. For example, shredded cabbage is cooked in one minute, fresh green beans in three minutes, small to medium-sized potatoes cook in five minutes (depending on thickness and type), and a whole "roast" chicken takes only twenty minutes. It is often used to simulate the effects of long braising or simmering in shorter periods of time. Some pressure cookers do not reach 15 psi at their highest pressure, which means cooking times for recipes using 15 psi will need to be increased by a few minutes [1].

The materials used for making cookers are generally aluminium and stainless steel. The former may be stamped and buffed or anodised, but this metal is unsuitable for the dishwasher. Expensive stainless steel pressure cookers are made with heavy, three-ply, or copper-clad bottoms for uniform heating. Most modern units are dishwasher safe, although some manufacturers may recommend washing by hand. A gasket forms an airtight seal which does not allow air or steam to escape between the pan and the lid, the only way the steam can escape is through a regulator on the lid when the pressure has built up (or if the regulator is blocked, through a safety valve). Sometimes the gasket is referred to as a sealing ring.

To meet Wikipedia's quality standards, this article or section may require cleanup because it is in a list format that may be better presented using prose. You can help by converting this section to prose, if appropriate. Editing help is available. This section has been tagged since October 2007.

• Cooks foods much faster compared to other methods.
• Uses less fuel than boiling/steaming the same quantity in an ordinary pot, due to the shorter cooking time.
• Hygienic compared to open cooking in a pot or utensil. The food is cooked above the boiling point of water, killing more germs.^{[citation needed]}
• Nutrients of food are better retained in pressure cooking.^{[citation needed]}
• Easy to cook with in comparison to other modern gadgets.
• Pressure cookers can be used to prepare a wide variety of different recipes, covering most cooking styles and foods.
• Allows higher quality cooking at high altitudes (see below section).
• The pressure cooker pan can be used as an ordinary saucepan for cooking larger quantities of food.
• Several foods can be cooked together in the pressure cooker. Besides saving fuel, this reduces the amount of washing up.
• Easy to clean pressure cooker after cooking.
• Kitchen is kept cleaner because, compared to traditional, open boiling, almost no steam and oils escape to the atmosphere to end up deposited on the walls.
• Due to the tight lid it can be used on board boats and other moving vehicles.

Pressure cookers have a reputation as a dangerous method of cooking with the risk of explosion. Early pressure cookers equipped with only a primary safety valve were at risk of explosion if poorly maintained, allowing food residues to contaminate the release valve. Modern pressure cookers typically have two or three independent safety mechanisms, as well as some additional safety features required for UL approval or the equivalent in other countries, such as an interlock to prevent opening the lid while internal pressure exceeds atmospheric pressure.

Modern pressure cookers employ several safety features, such as a lid interlock and a gauge to indicate when the cooker is pressurized. The pressure cannot build up unless the lid is properly closed and locked in place.

A regulator releases steam when the pressure exceeds the designed pressure for the cooker; this usually takes the form of a weighted stopper, commonly called "the rocker," or "vent weight". This weighted stopper is lifted by the steam pressure, allowing excess pressure to escape. There is usually a backup pressure release mechanism (a safety valve of sorts) that may employ any of a number of different techniques to release pressure quickly if the primary pressure release mechanism fails (for example, if food jams the steam discharge path). One such method is in the form of a hole in the lid blocked by a plug of low melting-point alloy. If the internal temperature (and hence pressure) gets too high, the metal plug will melt, resulting in release of pressure. Another technique takes the form of a rubber grommet with a metal insert at the center. At a sufficiently high pressure, the grommet will distort and blow out of its mounting hole, rapidly releasing the pressure. A common safety feature is the design of the gasket, which expands and releases excess pressure downwards between the lid and the pan (if the pressure cooker is heated on a gas burner, this downward release of pressure can be strong enough to extinguish the gas flames). In some pressure cookers, excess pressure forces the pressure indicator above its housing which releases the pressure vertically upwards.

A pressure cooker is often used by mountain climbers to compensate for the low atmospheric pressure at a very high altitude. Under these circumstances water boils at temperatures significantly below 100 °C and without the use of a pressure cooker, may leave boiled foods undercooked, as described in Charles Darwin's Voyage of the Beagle:

At the place where we slept water necessarily boiled, from the diminished pressure of the atmosphere, at a lower temperature than it does in a less lofty country; the case being the converse of that of a Papin's digester. Hence the potatoes, after remaining for some hours in the boiling water, were nearly as hard as ever. The pot was left on the fire all night, and next morning it was boiled again, but yet the potatoes were not cooked. I found out this, by overhearing my two companions discussing the cause, they had come to the simple conclusion, "that the cursed pot [which was a new one] did not choose to boil potatoes."

Some food toxins can be reduced by pressure cooking. A Korean study of aflatoxins in rice (associated with Aspergillus fungus) showed that pressure cooking was capable of reducing aflatoxin concentrations to 12 to 22 percent of the level in the uncooked rice.^[1]

• Pressure frying

• The Physics of Pressure Cooker, Dr. John Knox, Idaho State University
• How pressure cooking works from Presto, a manufacturer.
• Miss Vickie's Pressure Cooker Recipes

v • d • e Cooking techniques
Cooking under heat	Baking · Frying · Deep-frying · Boiling · Braising · Grilling/Broiling · Roasting · Sautéing · Stir frying · Poaching · Steaming · Pressure cooking · Pressure frying · Simmering · Clay pot cooking
Cooking without heat	Smoking · Marination
Food preservation	Canning · Drying · Pickling · Refrigeration · Salting · Smoking
Par-cook	Blanching · Parboiling
Other Techniques	Creaming · Fermenting · Outdoor cooking · Scalding · Tempering