Pressure cooking 52991 224871535 2008-07-10T19:56:27Z 141.116.57.142 /* Advantages */ Made "prion" a wikiword. {{redirect|Pressure cooker}} {{multipleissues | POV = May 2008 | refimprove = May 2008 | copyedit = June 2008 | inappropriate person = June 2008 }} [[Image:Pressure cooker.jpg|thumb|300px|A pressure cooker]] '''Pressure cooking''' is a method of cooking in a [[pressure vessel|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 higher temperature 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 [[Sterilization (microbiology)|sterilize]] materials is known as an [[autoclave]]. In the food industry, pressure cookers are often referred to as [[retort]]s. == Design == Pressure cookers are generally made from [[aluminium]] or [[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 bottom ([[heat spreader]]) for uniform heating, since stainless steel has lower [[thermal conductivity]]. 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 seal the gasket, some pressure cookers have a breach lock with flanges that interlock when you turn and tighten the lid on the pot. Others, like Hawkins<ref>''[http://www.hawkinscookers.com/downloads/pc_catalog.pdf Hawkins Pressure Cookers]''</ref> have slightly oval lids and openings. With these, you insert the lid at an angle, then turn the lid to fit the pot. A spring arrangement, in Hawkins' case the lid arm with a hook to the pot arm, holds the lid in the right place. When cooking, the pressurized steam inside keeps lids tightly on. The food to be made is placed in the pressure cooker, along with some amount of water. The vessel is then sealed and placed on a heat source (e.g. a [[Kitchen stove|stove]]). When the water reaches the [[boiling]] point at [[atmospheric pressure]] it begins to boil, but since the produced [[steam]] in the pressure cooker cannot escape the pressure rises, consequently raising the internal boiling point. Once the pressure increases to the designed amount above air pressure a [[relief valve]] opens, releasing steam and preventing the pressure from rising any further. Most pressure cookers sold in the U.S. have an internal pressure setting of about 100 kPa (15 psi) over atmospheric pressure, the standard determined by the [[United States Department of Agriculture|USDA]] in [[1917]]<ref>''[http://www.missvickie.com/workshop/pressure.html All About Pressure Settings]''</ref> . At around this pressure boost relative to sea-level atmospheric pressure, water boils at 125&nbsp;°C (257&nbsp;°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. Brown rice and lentils and beans can be cooked in 8 minutes instead of 45. Pressure cookers are often heavy because they need to be strong, and because they are often used to sterilise jams and other preserves and their many bottles at harvest time, so are big. Some pressure cookers are manufactured for camping, and can be as low as 1208g for a 4 litre pot. Pressure cooking is often used to simulate the effects of long [[braising]] or [[simmering]] in shorter periods of time. Some pressure cookers have a lower maximum pressure, or can be adjusted to different maximum pressures; cooking times will vary accordingly. This is often done by having differently-weighted regulator weights. However, there seems to be little reason to use the lesser pressures. Since pressure cooking depends on the production of steam, the process cannot easily be used for methods of cooking that produce little steam, such as [[roasting]], [[pan-frying]] or [[deep-frying]]. == Advantages == Foods are cooked much faster than other methods, (except perhaps the [[microwave]]), and with much less water than boiling, so dishes can be ready sooner. Less energy is required than when boiling, steaming or oven cooking, particularly if multiple foods are cooked at once. Since less water is necessary, the foods come to cooking temperature faster. The food is cooked above the boiling point of water, killing all germs and viruses. (But note that some toxins, eg [[prion|prions]], are more thermostable, and will not be neutralised.) The pressure cooker can also be used as an effective steriliser, for jam pots and glass baby bottles for example, or for water while camping. The medical [[autoclave]] is just a pressure cooker for sterilising medical instruments. With pressure cooking, heat is very evenly, deeply, and quickly distributed. Many pounds of vegetables or meat can be quickly cooked with just a cup of water - immersion of the food in boiling water is not necessary. Since foods need not be immersed, vitamins and minerals are not leached(dissolved) away by water. Since steam surrounds the food, foods are not oxidised by air exposure at heat, so [[asparagus]], [[broccoli]], and so on retain their bright green colours and vitamins. The pressure cooker speeds cooking considerably at high altitudes, where the low atmospheric pressure otherwise reduces the boiling point of water and hence reduces water's effectiveness for cooking or preparing hot beverages. This is especially useful for mountain climbers at very high altitudes, reducing cooking time and fuel requirements. [[Mountaineers]] and winter campers find the pressure cooker a very valuable tool for melting snow and ice. In an ordinary pot, melting snow is very slow because the water evaporates more than it melts. In a pressure cooker, not only is the steam kept in, it transfers heat to the rest of the snow and water very effectively. This is the same process that [[heat pipes]] use to transfer heat quickly and effectively. Due to its tight lid, it can be used without spillage on board boats and other moving vehicles, and to store cooked food for short times in a very sterile environment. Cooking in pressurised steam reduces washing up - foods do not burn or cake. A pressure cooker is cleaner compared to open cooking in a pot or utensil. The 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. Some claim that the pressure cooker is easy to cook with in comparison to other modern gadgets - it is certainly versatile. Pressure cookers can be used to prepare a wide variety of different recipes, covering most cooking styles and foods. The pressure cooker pan can be used as an ordinary [[saucepan]] for cooking larger quantities of food, reducing the number of utensils required. == Safety features == 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 [[Underwriters Laboratories|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 the insert blow out of its mounting hole, releasing the pressure. If the pressure gets still higher, the grommet itself will blow out. 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. == Use at high altitudes == 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&nbsp;°C and without the use of a pressure cooker, may leave boiled foods undercooked, as described in [[Charles Darwin]]'s ''Voyage of the Beagle'': {{quote|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 students designed a lightweight camping/mountaineering pressure cooker<ref>''[http://www.me.ucsb.edu/projects/poster_images07/pdf/153_team_3.pdf Magma Force Backpacking pressure cooker]''</ref> which weighs little more than a standard camping pot. == Use in food detoxification == Some food toxins can be reduced by pressure cooking. A Korean study of [[aflatoxin]]s in rice (associated with [[Aspergillus]] fungus) showed that pressure cooking was capable of reducing aflatoxin concentrations to 12% to 22% of the level in the uncooked rice.<ref>[http://www.sciencenews.org/articles/20060415/food.asp Food for Thought: Putting the Pressure on Poisons, Science News Online, April 15, 2006<!-- Bot generated title -->]</ref> == See also == *[[Pressure frying]] *[[Rice cooker]], many employ pressure cooking == References == {{reflist}} == External links == {{cookbook}} * [http://www.physics.isu.edu/~knox/papers/cooker.PDF The Physics of Pressure Cooker, Dr. John Knox, Idaho State University] * [http://www.megaforce.ca/products.php#cooker Electric Pressure Cooker] * [http://www.gopresto.com/information/school/works.php How pressure cooking works from Presto, a manufacturer.] {{Cooking Techniques}} [[Category:Cooking techniques]] [[ca:Olla de pressió]] [[cs:Papinův hrnec]] [[de:Schnellkochtopf]] [[es:Olla a presión]] [[eo:Prempoto]] [[fr:Autocuiseur]] [[ko:압력솥]] [[it:Pentola a pressione]] [[nl:Hogedrukpan]] [[ja:圧力鍋]] [[pl:Szybkowar]] [[pt:Panela de pressão]] [[simple:Pressure cooker]] [[sl:Lonec na zvišan pritisk]] [[fi:Painekattila]] [[sv:Tryckkokare]] [[tr:Düdüklü tencere]] [[zh:壓力鍋]]