Editing Pressure cooker (section)

== Operation ==

=== Liquid ===

Pressure cooking always requires a water-based liquid to generate the steam to raise the pressure within the cooker. Pressure cooking cannot be used for cooking methods that produce little steam such as [[roasting]], [[pan frying]], or [[deep frying]]. A minimum quantity of liquid is required to create and maintain pressure, as indicated in the manufacturer's instruction manual. For venting cookers more liquid is required for longer cooking times. This is not desirable for food requiring much less liquid, but recipes and books for pressure cookers take this into account.

=== Assembling ===
Food is placed inside the pressure cooker with a small amount of water or other liquid such as [[Stock (food)|stock]]. Food is either cooked in the liquid or above the liquid for [[steaming]]; the latter method prevents the transfer of flavors from the liquid.

[[Sauce]]s which contain starch thickeners can tend to burn onto the interior base of the pressure cooker which may prevent the cooker from reaching operating pressure. Because of this issue, sauces may require thickening or [[Reduction (cooking)|reduction]] after pressure cooking.

With ''pot in pot'' pressure cooking, some or all of the food is placed in an elevated pot on a trivet above water or another food item which generates the steam. This permits the cooking of multiple foods separately, and allows for minimal water mixed with the food, and thicker sauces, which would otherwise scorch onto the bottom of the pan.

=== Bringing to pressure ===

The lid is closed, the pressure setting is chosen and the pressure cooker is heated to boil the liquid. The cooker fills with steam and vents air. As the internal temperature rises, the pressure rises until it reaches the desired [[gauge pressure]].

It usually takes several minutes for the pressure cooker to reach the selected pressure level. It can take 10 minutes or longer depending on the quantity of food, the temperature of the food (cold or frozen food delays pressurization), the amount of liquid, the power of the heat source, and the size of the pressure cooker. There is typically a pop-up indicator that shows that the cooker has pressure inside, but it does not reliably signal that the cooker has reached the selected pressure. The pop-up indicator shows the state of the interlock which prevents the lid from being opened while there is any internal pressure. Manufacturers may use their own terminology for this, such as calling it a ''"locking indicator."''

Timing the recipe begins when the selected pressure/pressure is reached. Once the cooker reaches full pressure, the heat is lowered to maintain the pressure. With pressure cookers accurate timing is essential using an audible [[timer]].

With first generation designs, the pressure regulator weight begins levitating above its [[nozzle]], allowing excess steam to escape. In second generation pressure cookers, either a [[relief valve]] subsequently opens, releasing steam to prevent the pressure from rising any further or a rod rises with markers to indicate the pressure level, without constantly venting steam. At this stage, the heat source is reduced to the lowest possible heat that still maintains pressure, as extra heat wastes energy and increases liquid loss. In third generation pressure cookers, the device will detect the vessel has reached the required cooking temperature/pressure and will maintain it for the programmed time, generally without further loss of steam.

Recipes for foods using [[Leavening agent|raising agents]] such as steamed puddings call for gentle pre-steaming, without pressure, in order to activate the raising agents prior to cooking and achieve a light, fluffy texture.

=== Food containers ===

Small containers such as plastic pudding containers can be used in a pressure cooker, if the containers (and any covering used) can withstand temperatures of {{convert|130|C|F}} and are not placed directly on the interior base. The containers can be used for cooking foods that are prone to burning on the base of the pressure cooker. A lid for the container may be used if the lid allows some steam to come into contact with the food and the lid is securely fitted; an example is foil or greaseproof paper, [[pleat]]ed in the center and tied securely with string. Containers that are cracked or have otherwise sustained damage are not suitable. Cooking time is longer when using covered containers because the food is not in direct contact with the steam. Since non-metal containers are poorer [[Thermal conductivity|heat conductors]], the type of container material stated in the recipe cannot be substituted without affecting the outcome. For example, if the recipe time is calculated using a stainless steel container and a [[plastic container]] is used instead, the recipe will be undercooked, unless the cooking time is increased. Containers with thicker sides, e.g., oven-proof glass or ceramic containers, which are slower to conduct heat, will add about 10 minutes to the cooking time. Liquid can be added inside the container when pressure cooking foods such as rice, which need to absorb liquid in order to cook properly.

=== Pre-frying ingredients ===

The flavor of some foods, such as meat and onions, can be improved by gently cooking with a little pre-heated cooking oil, butter or other [[fat]] in the open pressure cooker over medium heat for stove-top models (unless the manufacturer advises against this) before pressure cooking, while avoiding overheating the empty pressure cooker not heating the empty cooker with the lid and gasket in place to avoid damage. Electric pressure cookers usually have a "saute" or "brown" option for frying ingredients. The pressure cooker needs to cool briefly before adding liquid; otherwise some of the liquid will evaporate instantly, possibly leaving insufficient liquid for the entire pressure cooking time; if [[deglazing (cooking)|deglazing]] the pan, more liquid may need to be added.

=== Pressure release methods ===

After cooking, there are three ways of releasing the pressure, either quickly or slowly, before the lid can be opened. Recipes for pressure cookers state which release method is required at the end of the cooking time for proper results. Failure to follow the recommendation may result in food that is under-cooked or over-cooked.

To avoid opening the pressure cooker too often while cooking different vegetables with varying cooking times, the vegetables that take longer to cook can be cut into smaller pieces and vegetables that cook faster can be cut into larger pieces.

To inspect the food, the pressure cooker needs to be opened, which halts the cooking process. With a conventional [[saucepan]], this can be done in a matter of seconds by visually inspecting the food.

==== Manual, normal, regular, or automatic release ====

This method is sometimes called a ''quick release,'' not to be confused with the cold water release (mentioned below). It involves the quick release of vapor by gradually lifting (or removing) the valve, pushing a button, or turning a dial. It is most suitable to interrupt cooking to add food that cooks faster than what is already in the cooker. For example, since meat takes longer to cook than vegetables, it is necessary to add vegetables to [[stew]] later so that it will cook only for the last few minutes. Releasing the steam with care avoids the risk of being scalded by the rapid release of hot steam. This release method is not suitable for foods that foam and froth while cooking; the hot contents might spray outwards due to the pressure released from the steam vent. Pressure cookers should be operated with caution when releasing vapour through the valve, especially while cooking foamy foods and liquids ([[lentil]]s, [[bean]]s, grains, milk, [[gravy]], etc.){{citation needed|date=September 2019}} This release method takes about two minutes to release the pressure before the lid can be opened.

==== Natural release ====

The natural release method allows the pressure to drop slowly. This is achieved by removing the pressure cooker from the heat source and allowing the pressure to lower without action. It takes approximately 10 to 15 minutes (possibly longer) for the pressure to disappear before the lid can be opened. On many pressure cookers, a coloured indicator pin will drop when the pressure has gone. This natural release method is recommended for foods that foam and froth during cooking, such as rice, legumes, or recipes with [[Leavening agent|raising agents]] such as steamed puddings. The texture and tenderness of meat cooked in a pressure cooker can be improved by using the natural release method. The natural release method finishes cooking foods or recipes that have longer cooking times because the inside of the pressure cooker stays hot. This method is not recommended for foods that require very short cooking times, otherwise the food overcooks.

==== Cold water quick release ====

This method is the fastest way of releasing pressure with portable pressure cookers, but can be dangerous if performed incorrectly.  Hence it is safer to release pressure by using the other methods. The manufacturer's instruction book may advise against the cold water release or require it to be performed differently.

The cold water release method involves using slow running cold tap water, over the edge of the pressure cooker lid, being careful to avoid the steam vent or any other valves or outlets, and never immersing the pressure cooker under water, otherwise steam can be ejected from under the lid, which could cause [[scalding]] injury to the user; also the pressure cooker lid can be permanently damaged by an internal [[vacuum]] if water gets sucked into the pressure cooker, since the incoming water blocks the inrush of air.

The cold water release is most suitable for foods with short cooking times. It takes about 20 seconds for the cooker to cool down enough to lower the pressure so that it can be safely opened. This method is not suitable for electric pressure cookers, as they are not immersible. This type of pressure cooker cannot be opened with a cold water quick-release method.

The cold water release method is not recommended when cooking pulses e.g. red kidney beans, as the sudden release of pressure can cause the bean to burst its skin.

=== Pressure settings ===

Most pressure cookers have a cooking (operating) pressure setting between 0.8–1 bar (11.6–15 psi) (gauge) so the pressure cooker operates at 1.8 to 2.0 bar (absolute).  The standard cooking pressure of 15 psi gauge was determined by the [[United States Department of Agriculture]] in 1917. At this pressure, water boils at {{convert|121|C|F}} (described in [[vapour pressure of water]] article).

The higher temperature causes food to cook faster; cooking times can typically be reduced to one-third of the time for conventional cooking methods. The actual cooking time also depends on the pressure release method used after timing ''(see [[#Pressure release methods|Pressure release methods]] for details)'' and the thickness and density of the food, since thicker (and denser) foods take longer to cook. Meat joints and some other foods like sponge puddings and [[Christmas pudding]]s are typically timed according to their weight. Frozen foods need extra cooking time to allow for thawing.

When pressure cooking at 1 bar/15 psi (gauge), approximate cooking times are one minute for shredded cabbage, seven minutes for boiled potatoes (if cut small, not diced) and three minutes for fresh green beans.  If the pressure is released naturally after timing ''(see [[#Pressure release methods|Pressure release methods]] for details),'' cooking times are even shorter. Food cooks more quickly when cut into smaller pieces.

Some recipes may require cooking at lower than 1 bar/15 psi (gauge) e.g. fresh vegetables, as these can easily overcook. Many pressure cookers have 2 or more selectable pressure settings or weights.

Some pressure cookers have a lower or higher ''maximum'' pressure than 1 bar/15 psi (gauge) or can be adjusted to different pressures for some recipes; cooking times will increase or decrease accordingly. This is typically done by having different regulator weights or different pressure or temperature settings. Some pressure cookers operate at lower pressures than others. If the recipe is devised for a higher pressure and the pressure cooker does not reach that pressure, the cooking time can be increased to compensate.

=== Efficiency ===

Pressure cookers are considerably more expensive than conventional [[saucepan]]s of the same size.

The minimum quantity of water or liquid that keeps pressure cooker filled with steam is sufficient, so pressure cookers can use much less liquid than the amount required for conventional cooking. When less water or liquid is heated, the food reaches its cooking temperature faster and less energy is required than that of boiling, [[steaming]], or oven cooking. It is also not necessary to immerse food in water. Additionally, with non venting pressure cookers, steam isn't continually escaping, thus evaporation losses are non existent once it has reached pressure. Overall, energy used by third generation pressure cookers can be as much as 70% lower than conventional pan cooking.<ref>{{cite news | url=https://www.telegraph.co.uk/recommended/home/best-electric-pressure-cookers/ | title=The best pressure cookers, tried and tested in a kitchen | newspaper=The Telegraph | date=25 July 2019 | last1=Rear | first1=Jack }}</ref>

=== Effect on food ===
Pressure cooking requires much less water than conventional [[boiling]], so food can be ready sooner.

Because of this, [[vitamin]]s and [[Mineral (nutrient)|minerals]] are not leached (dissolved) away by water, as they would be if food were boiled in large amounts of water. Due to the shorter cooking time, vitamins are preserved relatively well during pressure cooking.<ref name="pmid7792260">{{cite journal |author=Yadav SK, Sehgal S |title=Effect of home processing on ascorbic acid and beta-carotene content of spinach (Spinacia oleracia) and amaranth (Amaranthus tricolor) leaves |journal=Plant Foods Hum Nutr |volume=47 |issue=2 |pages=125–31 |date=February 1995 |pmid=7792260 |doi=10.1007/bf01089261|s2cid=19736809 }}</ref>

Several foods can be cooked together in the pressure cooker, either for the same amount of time or added later for different times. Manufacturers provide steamer baskets to allow more foods to be cooked together inside the pressure cooker.

Not only is this steam energy transmitted quickly to food, it is also transmitted rapidly to any micro-organisms that are present, easily killing even the deadliest types that are able to survive at the boiling point. Because of this enhanced germ killing ability, a pressure cooker can be used as an effective sanitizer for [[jam]] pots, glass [[baby bottle]]s, or for water while [[camping]].

=== Foods unsuitable for pressure cooking ===
Some foods are not recommended for pressure cooking.  Foods such as [[noodle]]s, [[pasta]], [[cranberry|cranberries]], [[cereal]]s and [[oatmeal]] can expand too much, froth and sputter, potentially blocking the steam vent and creating an unsafe condition.<ref name=brev>{{Cite web |url=https://cdn.shopify.com/s/files/1/2052/6319/files/BPR700BSS_ANZ_IB.pdf?2146039452558888747 |title=Breville the Fast Slow Pro™ Instruction Booklet |website=shopify.com |format=PDF |access-date=13 November 2018}}</ref>