Editing Pressure cooker (section)

== Design ==
[[File:Pressure cooker oval lid.jpg|thumb|The regulator in this pressure cooker is a weight on a [[nozzle]] next to the handle on the lid.]]

Pressure cookers employ one or more regulators to control the pressure/temperature. All types have a calibrated pressure relief valve, as well as one or more emergency valves.

With the simplest types, once the desired pressure is reached, the valve opens, and steam escapes cooling the vessel and limiting the temperature. More advanced stovetop models have pressure indicators that permit the user to adjust the heat to prevent the steam from escaping. Third generation types automatically measure the state of the vessel and control the power so as to not release steam in operation.

=== Capacity ===
Pressure cookers are available in different capacities for cooking larger or smaller amounts, with 6 litres' capacity being common.  The maximum capacity of food is less than the advertised capacity because pressure cookers can only be filled up to 2/3 full, depending on ingredients and liquid (see Safety features section).{{citation needed|date=September 2019}}

=== Pan ===
* Metal pan body
* Pan handles, usually one each on opposite ends, for carrying the cooker with both hands

Because of the forces that pressure cookers must withstand, they are usually heavier than conventional pots of similar size. The increased weight of conventional pressure cookers makes them unsuitable for applications in which saving weight is a priority, such as [[camping]]. Nonetheless, small, lightweight pressure cookers are available for mountain climbers ''(see [[#High altitudes|High altitudes]])''.

=== Lid ===
Lids usually have a number of features:
* Lid handle, usually with a locking device button or slider that "clicks" shut and prevents removal while cooking
* [[Gasket]] (also known as a "sealing ring") that seals the cooker airtight
* Steam vent with a pressure regulator on top (either a weight or spring device) that maintains the pressure level in the pan
* Pressure indicator pin, for showing the presence or absence of any pressure, however slight
* Safety devices on the lid (typically over-pressure and/or over-temperature pressure release valves)

=== Gasket ===
A gasket or sealing ring, made from either rubber or [[silicone]], forms a gas-tight seal that does not allow air or steam to escape between the lid and pan. Normally, the only way steam can escape is through a [[Pressure regulator|regulator]] on the lid while the cooker is pressurized. If the regulator becomes blocked, a [[safety valve]] provides a backup escape route for steam.{{citation needed|date=September 2019}}

To seal the gasket there are several main methods used. Each determines the design of the pressure cooker:
* The ''twist-on'' design has slots on the lid engaging with [[flange]]s on the body, similar to a lid on a glass jar, that works by placing the lid on the pot and twisting it about 30° to lock it in place. A common modern design, it has easily implemented locking features that prevent the removal of the lid while under pressure.
* The ''center screw'' design has a bar that is slotted in place over the lid and a screw tightened downward to hold the lid on. Though an older design, it is still produced due to its ease of construction and simplicity.
* The ''bolt-down'' design has flanges on both its lid and its body for bolts to be passed through, and usually uses [[Wingnut (hardware)|wingnuts]] that hinge on the body and so are never fully removed from the cooker; this sealing design is typically used for larger units such as canning retorts and autoclaves. It is very simple to produce, and it can seal with simple and inexpensive [[gaskets]].
* The ''internally fitted lid'' design employs an oval lid that is placed inside and presses outward; the user inserts the lid at an angle, then turns the lid to align it with the pot opening on top because the lid is larger than the opening. A spring arrangement holds the lid in place until the pressure forms and holds the lid tightly against the body, preventing removal until the pressure is released.

[[Gasket]]s (sealing rings) require special care when cleaning (e.g., not washed with kitchen knives), unlike a standard [[lid (container)|lid]] for a saucepan. Food debris, fats, and oils must be cleaned from the gasket after every use. Gasket/sealing rings need replacing with a new one about once a year (or sooner if it is damaged e.g. a small split). A very dry gasket can make it difficult or impossible to close the lid. Smearing the gasket sparingly with vegetable oil alleviates this problem (using too much vegetable oil can make the gasket swell and prevent it sealing properly). A gasket that has lost its flexibility makes bringing the cooker up to pressure difficult as steam can escape before sufficient pressure is generated to provide an adequate seal; this is usually a sign that the gasket needs replacing with a new one.  Oiling the gasket with vegetable oil may alleviate the problem temporarily, but a new gasket is often required.{{Original research inline|date=December 2022}}

Pressure cooker manufacturers sell replacement gaskets and recommend their replacement at regular intervals e.g. annually.
If the pressure cooker has not been used for a long time, the gasket and other rubber or silicone parts will dry out and will likely need replacing.

=== Safety features ===
Early pressure cookers equipped with only a primary safety valve risked explosion from food blocking the release valve. On modern pressure cookers, food residues blocking the steam vent or the liquid boiling dry will trigger additional safety devices. Modern pressure cookers sold from reputable manufacturers have sufficient safety features to prevent the pressure cooker itself from exploding. When excess pressure is released by a safety mechanism, debris of food being cooked may also be ejected with the steam, which is loud and forceful. This can be avoided if the pressure cooker is regularly cleaned and maintained in accordance with the manufacturer's instructions and never overfilled with food and/or liquid.<ref>{{Cite web |date=2024-09-13 |title=Pressure Cooker Dos and Don'ts: Avoid These Common Mistakes |url=https://www.omichef.com/blogs/news/pressure-cooker-dos-and-donts-avoid-these-common-mistakes |access-date=2025-04-19 |website=OmiChef |language=en}}</ref>

Modern pressure cookers typically have two or three redundant safety valves and additional safety features, such as an [[Interlock (engineering)|interlock]] lid that prevents the user from opening the lid when the internal pressure exceeds atmospheric pressure, preventing accidents from a sudden release of hot liquid, steam and food. If safety mechanisms are not correctly in place, the cooker will not pressurize the contents. Pressure cookers should be operated only after reading the instruction manual, to ensure correct usage. Pressure cooker failure is dangerous: a large quantity of scalding steam and water will be forcefully ejected and if the lid separates it may be propelled with considerable force. Some cookers with an internally fitted lid may be particularly dangerous upon failure as the lid fits tighter with increasing pressure, preventing the lid from deforming and venting around the edges. Due to these dangers pressure cookers are generally over-engineered in a safety regard and some countries even have regulations to prevent the sale of non-compliant cookers.{{citation needed|date=September 2019}}

For first generation pressure cookers with a weighted valve or "jiggler", the primary safety valve or regulator is usually a weighted stopper, commonly called "the rocker" or "vent weight". This weighted stopper is lifted by the steam pressure, allowing excess pressure to be released. There is a backup pressure release mechanism that releases pressure quickly if the primary pressure release mechanism fails (e.g., food jams the steam discharge path). One such method is a hole in the lid that is blocked by a low melting point [[alloy]] plug and another is a rubber [[grommet]] with a metal insert at the center. At a sufficiently high pressure, the grommet will distort and the insert will blow out of its mounting hole to release pressure. If the pressure continues to increase, the grommet itself will blow out to release pressure. These safety devices usually require replacement when activated by excess pressure. Newer pressure cookers may have a self-resettable spring device, fixed onto the lid, that releases excess pressure.{{citation needed|date=September 2019}}

On second generation pressure cookers, a common safety feature is the [[gasket]], which expands to release excess pressure downward between the lid and the pot. This release of excess pressure is forceful and sufficient to extinguish the flame of a [[gas stove]].{{citation needed|date=September 2019}}

Pressure cookers sold in the [[European Union]] (EU) must comply with the [[Pressure Equipment Directive]].<ref>{{cite web |url=http://ec.europa.eu/enterprise/sectors/pressure-and-gas/documents/index_en.htm |title=Pressure equipment and gas appliances |date=2 February 2012 |url-status=dead|archive-url=https://web.archive.org/web/20120405105453/http://ec.europa.eu/enterprise/sectors/pressure-and-gas/documents/index_en.htm |archive-date=5 April 2012}}</ref>

====Maximum fill levels====
The recommended maximum fill levels of food/liquid avoids blockage of the steam valve or developing excess pressure: two-thirds full with solid food, half full for liquids and foods that foam and froth (e.g., rice, pasta; adding a tablespoon of cooking oil minimizes foaming),<ref name="Wise">{{cite book |author=Wise, Victoria |title=The Pressure Cooker Gourmet: 225 Recipes for Great-Tasting, Long-Simmered Flavors in Just Minutes |publisher=Harvard Common Press |location=Harvard, Mass |year=2005 |isbn=1-55832-201-9|page = 262}}</ref> and no more than one-third full for [[Pulse (legume)|pulses]] (e.g., [[lentil]]s).{{citation needed|date=February 2020}}

=== Accessories ===
* Steamer basket
* Trivet for keeping the steamer basket above liquid
* Metal divider, for separating different foods in the steamer basket e.g. vegetables
* Inner pot, for pot-in-pot pressure steaming

=== Materials ===
[[File:Aluminum pressure cooker kazan from Afghanistan.jpg|thumb|Aluminum Afghani pressure cooker ([[Kazan (cookware)|kazan]]), similar to those found to contain high levels of lead.]]

Pressure cookers are typically made of [[aluminum]] (aluminium) or [[stainless steel]]. Aluminum pressure cookers may be [[Stamping (metalworking)|stamped]], [[Polishing (metalworking)|polished]], or [[Anodizing|anodized]], but all are unsuitable for the [[dishwasher]]. They are cheaper, but the aluminum is reactive to acidic foods,<ref>{{Cite web |title=Aluminum {{!}} Public Health Statement {{!}} ATSDR |url=https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=1076&toxid=34 |access-date=2024-08-19 |website=wwwn.cdc.gov |quote=Eating large amounts of processed food containing aluminum additives or frequently cooking acidic foods in aluminum pots may expose a person to higher levels of aluminum than a person who generally consumes unprocessed foods and uses pots made of other materials (e.g., stainless steel or glass). However, aluminum levels found in processed foods and foods cooked in aluminum pots are generally considered to be safe.}}</ref> whose flavors are changed in the reactions,{{citation needed|date=September 2022}} and are less durable than stainless steel pressure cookers. Some [[Kazan (cookware)|aluminum pressure cookers]] from Afghanistan are known to be contaminated with lead and imported pots were responsible for the lead poisoning of Afghani refugees in [[Washington (state)|Washington state]] in 2019.<ref name=":3">{{cite web | title=Public Health Advisory Related to Aluminum Afghan Kazan Pressure Cookers | website=Boston.gov | date=16 May 2023 | url=https://www.boston.gov/news/public-health-advisory-related-aluminum-afghan-kazan-pressure-cookers | ref={{sfnref | Boston.gov | 2023}} | access-date=18 August 2024}}</ref><ref name=":2">{{Cite journal |last1=Fellows |first1=Katie M. |last2=Samy |first2=Shar |last3=Rodriguez |first3=Yoni |last4=Whittaker |first4=Stephen G. |date=May 2022 |title=Investigating aluminum cookpots as a source of lead exposure in Afghan refugee children resettled in the United States |journal=Journal of Exposure Science & Environmental Epidemiology |language=en |volume=32 |issue=3 |pages=451–460 |doi=10.1038/s41370-022-00431-y |pmid=35501355 |issn=1559-064X|pmc=9119854 }}</ref><ref>{{Cite journal |last1=Fellows |first1=Katie M. |last2=Samy |first2=Shar |last3=Whittaker |first3=Stephen G. |date=2024-05-21 |title=Evaluating metal cookware as a source of lead exposure |url=https://www.nature.com/articles/s41370-024-00686-7?fromPaywallRec=false |journal=Journal of Exposure Science & Environmental Epidemiology |language=en |pages=1–9 |doi=10.1038/s41370-024-00686-7 |issn=1559-064X|doi-access=free |pmc=12069085 }}</ref>

Higher-quality stainless steel pressure cookers are made with heavy, three-layer, or [[Copper-clad steel|copper-clad]] bottoms ([[heat spreader]]) for uniform heating because stainless steel has lower [[thermal conductivity]]. Most modern stainless steel cookers are dishwasher safe, although some manufacturers may recommend washing by hand. Some pressure cookers have a [[Non-stick surface|non-stick]] interior.