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Pressure cooking is the process of cooking food under high pressure steam and water or a water-based cooking liquid, in a sealed vessel known as a pressure cooker. High pressure limits boiling, and creates higher cooking temperatures which cook food far more quickly.

The pressure cooker was invented in the seventeenth century by the physicist Denis Papin, and works by expelling air from the vessel, and trapping steam produced from the boiling liquid. This is used to raise the internal pressure up to one atmosphere above ambient and gives higher cooking temperatures between 100–121 °C (212–250 °F). Together with high thermal heat transfer from steam it permits cooking in between a half and a quarter the time of conventional boiling.

According to New York Times Magazine, 37% of U.S. households owned at least one pressure cooker in 1950. By 2011, that rate dropped to only 20%. Part of the decline has been attributed to fear of explosion, although this is extremely rare with modern pressure cookers, along with competition from other fast cooking devices, such as the microwave oven.

In 1679, French physicist Denis Papin, better known for his studies on steam, invented the airtight cooker used steam pressure to raise the water"s boiling point, thus cooking food more quickly. In 1681 Papin presented his invention to the Royal Society of London as a scientific study; he was later elected as a member.

In 1918, Spain granted a patent for the pressure cooker to José Alix Martínez from Zaragoza. Martínez named it the olla exprés, literally "express cooking pot", under patent number 71143 in the Boletín Oficial de la Propiedad Industrial.360 recipes for cooking with a pressure cooker.

In 1935, the Automa pressure cooker was introduced. Mountaineers attempting to climb Mount Everest took it along with them to cook in higher altitudes.

In 1938, Alfred Vischer presented his invention, the Flex-Seal Speed Cooker, in New York City. Vischer"s pressure cooker was the first designed for home use, and its success led to competition among American and European manufacturers.1939 New York World"s Fair, the National Pressure Cooker Company, later renamed National Presto Industries, introduced its own pressure cooker.

Today, most pressure cookers are variations on the first-generation cookers, with the addition of new safety features such as a mechanism that prevents the cooker from being opened until it is entirely depressurized.

These include an electric heat source that is automatically regulated to maintain the operating temperature and pressure. They also include a spring-loaded valve (as described above) and are typically non venting during cooking.

Second-generation electric, with digital controller. Delayed cooking becomes possible and the controller shows a countdown timer when working pressure is reached.

Third-generation electric, with smart programming, which includes pre-set cooking times and settings based on heating intensity, temperature, pressure and duration.

Some pressure cookers are multifunctional (multicookers): pressure cooker, saute/browning, slow cooker, rice cooker, egg cooker, yogurt maker, steamer, sous vide, canner, and stockpot warmer that can also be used to keep cooked food warm.Ninja Foodi pressure cooker, which was the first pressure cooker that could also air fry, several other pressure cooker manufacturers, including Instant Pot, have come out with their own pressure cookers that can air fry, which are now known as pressure air fryers. Pressure air fryers have two separate lids, one for pressure cooking, and one for air frying.

At standard pressure the boiling point of water is 100 °C (212 °F). With any food containing or cooked with water, once the temperature reaches the boiling point, any excess heat causes some of the water to vaporize into steam efficiently carrying away heat keeping the food temperature at 100 °C.

In a sealed pressure cooker, as the water boils, the steam is trapped in the cooker which raises the pressure. However, the boiling point of water increases with pressure resulting in superheated water.

In a sealed pressure cooker the volume and amount of steam is fixed, so the temperature can be controlled either directly or by setting the pressure (such as with a pressure release valve).

For example, if the pressure reaches 1 bar or 100 kPa (15 psi) above the existing atmospheric pressure, the water will have reached a temperature of approximately 120 °C (248 °F) which cooks the food much faster.

Pressure cookers also use steam and water to rapidly transfer the heat to the food and all parts of the vessel. While, compared to an oven, a pressure cooker"s 120 °C is not particularly high, ovens contain air which is subject to thermal boundary layer effects which greatly slows heating, whereas pressure cookers flush air from the cooking vessel during warm up and replace it with hot steam. For items not placed within the liquid, as this steam condenses on the food it transfers water"s latent heat of vaporization, which is extremely large (2.275 kJ/g), to the surface, rapidly bringing the surface of the food up to cooking temperature. Because the steam condenses and drips away, no significant boundary layer forms and heat transfer is exceptionally efficient, and food heats much faster and more evenly.

However some recipes require browning to develop flavors as during roasting or frying. Higher temperatures are attainable with conventional cooking where the surface of the food can dry out. Such browning occurs via the Maillard reaction, at temperatures higher than the roughly 120 °C (248 °F) achieved in pressure cooking. Because those temperatures are not reached in pressure cooking, foods are generally browned by searing them, either in the open pressure cooker or another pan beforehand.

A pressure cooker can be used to compensate for lower atmospheric pressure at high elevations. The boiling point of water drops by approximately 1°C per every 294 metres of altitude (see: High-altitude cooking), causing the boiling point of water to be significantly below the 100 °C (212 °F) at standard pressure. This is problematic because temperatures above roughly 90°C are necessary to cook many common vegetables in a reasonable time. For example, on the summit of Everest (8,848 m (29,029 ft)), the boiling point of water would be only 70 °C (158 °F). Without the use of a pressure cooker, many boiled foods may remain undercooked, as described in Charles Darwin"s

Having crossed the Peuquenes [Piuquenes], we descended into a mountainous country, intermediate between the two main ranges, and then took up our quarters for the night. We were now in the republic of Mendoza. The elevation was probably not under 11,000 feet (3,400 m) [...]. 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.

When pressure cooking at high altitudes, cooking times need to be increased by approximately 5% for every 300 m (980 ft) above 610 m (2,000 ft) elevation. Since the regulators work off the pressure differential between interior and ambient pressure, the absolute pressure in the interior of a pressure cooker will always be lower at higher altitudes.

Weight is a concern with backpackers, so mountaineering pressure cookers are designed to operate at a lower differential pressure than stove-top units. This enables them to use thinner, and therefore lighter materials. Generally, the goal is to raise the cooking temperature enough to make cooking possible and to conserve fuel by reducing heat lost through boiling.Sherpas often use pressure cookers in base camp.

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.

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).

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

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 regulator on the lid while the cooker is pressurized. If the regulator becomes blocked, a safety valve provides a backup escape route for steam.

The twist-on design has slots on the lid engaging with flanges 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 bolt-down design has flanges on both its lid and its body for bolts to be passed through, and usually uses 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.

Gaskets (sealing rings) require special care when cleaning (e.g., not washed with kitchen knives), unlike a standard 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.

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.

Modern pressure cookers typically have two or three redundant safety valves and additional safety features, such as an 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.

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.

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.

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),pulses (e.g., lentils).

Pressure cookers are typically made of aluminum (aluminium) or stainless steel. Aluminum pressure cookers may be stamped, polished, or anodized, but all are unsuitable for the dishwasher. They are cheaper, but the aluminum is reactive to acidic foods, whose flavors are changed in the reactions, and less durable than stainless steel pressure cookers.

Higher-quality stainless steel pressure cookers are made with heavy, three-layer, or 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 interior.

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.

Food is placed inside the pressure cooker with a small amount of water or other liquid such as 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.

Sauces 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 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 the use of minimal water mixed with the food in the pot which permits thick sauces which would otherwise scorch onto the bottom of the pan to be cooked.

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 around 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 it, 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 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.

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 130 °C (266 °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, pleated 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 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.

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 the pan, more liquid may need to be added.

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.

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. Unlike the cold water release method, this release method does not cool down the pressure cooker. 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 (lentils, beans, grains, milk, gravy, etc.)

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 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.

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.

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 121 °C (250 °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 Christmas puddings 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

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.

Less energy is required than that of boiling, steaming, or oven cooking. Since less water or liquid has to be heated, the food reaches its cooking temperature faster. Using more liquid than necessary wastes energy because it takes longer to heat up; the liquid quantity is stated in the recipe. Pressure cookers can use much less liquid than the amount required for boiling or steaming in an ordinary saucepan. It is not necessary to immerse food in water. The minimum quantity of water or liquid used in the recipe to keep the pressure cooker filled with steam is sufficient. 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 pressure cookers can be as much as 70% lower than used by cooking in a pan.

Because of this, vitamins and 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.

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 bottles, or for water while camping.

Some foods are not recommended for pressure cooking. Foods such as noodles, pasta, cranberries, cereals and oatmeal can expand too much, froth and sputter, potentially blocking the steam vent and creating an unsafe condition.

An ≥ 121 °C) is a type of pressure cooker used by laboratories and hospitals to sterilize equipment. A stovetop autoclave is essentially a higher-pressure cooker with a gauge, used as an autoclave in poorer areas.

Pressure canners are large pressure cookers which have the capacity to hold jars used in canning. Pressure canners are specifically designed for home canning, whereas ordinary pressure cookers are not recommended for canning due to the risk of botulism poisoning, because pressure canners hold heat (≥ 115 °C) and pressure for much longer than ordinary pressure cookers; these factors are a critical part of the total processing time required to destroy harmful microbes such as bacterial spores.

A pressure air fryer (not to be confused with a pressure fryer) is a recent combination of a pressure cooker and an air fryer, with two separate lids, one for pressure cooking and one for air frying. The air frying lid has a convection fan in it that allows it to air fry foods, similar to an air fryer oven. This innovation was popularized by the Ninja Foodi Pressure Cooker, marketed as the first pressure cooker that can crisp and air fry.

A pressure oven is a recent combination of an oven and pressure cooker, usually as a countertop convection oven. They operate at low pressures, 10 kilopascals (1.5 psi), compared to other pressure cookers.rotisserie. Although having insufficient pressure for most conventional pressure cooking functions, they do also have non-pressure oven modes.

Rick Rodgers; Arlene Ward & Kathryn Russell (2000). Pressure Cooking for Everyone. Chronicle Books. p. 12. ISBN 9780811825252. Retrieved 30 June 2016.

Park, Je Won; Kim, Young-Bae (March 2006). "Effect of Pressure Cooking on Aflatoxin B in Rice". Journal of Agricultural and Food Chemistry. 54 (6): 2431–2435. doi:10.1021/jf053007e. PMID 16536630.

Wise, Victoria (2005). The Pressure Cooker Gourmet: 225 Recipes for Great-Tasting, Long-Simmered Flavors in Just Minutes. Harvard, Mass: Harvard Common Press. p. 262. ISBN 1-55832-201-9.

Borenstein, Seth (17 April 2013). "How does a pressure cooker bomb work?". MediaWorks TV. Archived from the original on 24 March 2016. Retrieved 13 November 2018.

"Burning Issue: Canning in Pressure Cookers". National Center for Home Food Preservation. September 2015. Archived from the original on 13 November 2018. Retrieved 13 November 2018.

The present invention in general relates to the microwave compatible cooking system to be used as home appliance for cooking foods and it more specifically relates to pressure cooking system to be used inside a microwave oven for cooking food containing steam at a pressure above the ambient pressure. The microwave pressure cooker described in this invention can be used to cook foods safely in various situations for domestic pressure cooking. This is a complete self contained system that can be used with any microwave oven provided with a chamber large enough to accommodate it and more specifically which has a safety lock means to manage safely pre-operation, during operation and post operation condition of the cooker. BACKGROUND OF THE INVENTION

Nowadays the use of number of microwave oven in public has grown at very high rate. There has been an increase in demand for specially designed and configured cooking vessels for use in microwave ovens to provide easy and convenient way of preparing foods in microwave ovens. Many attempts have been made in the manufacture of various types of cooking vessels, casserole dishes, various types of bowls, pressure cookers for microwave and the like, to be compatible with use in microwave ovens. PRIOR ART

U.S. Pat. No. 4,796,776 discloses a pressure cooker for use in microwave ovens includes a microwave permeable bowl-shaped container, a microwave permeable dome cover, and a steel locking ring permanently attached to the cover for maintaining the container and cover in fluid-tight seal during use. A safety-valve, formed of flexible tubing, encounters a projection of the container and is deformed into a closed configuration responsive to movement of the cover, relative to the container, toward a locking position. A pressure regulator valve, consisting of a metal core surrounded by an elastically deformable casing, which is positioned over a pressure control opening in the cover to maintain a selected operating pressure level in the pressure cooker.

U.S. Pat. No. 4,853,509 discloses a rice cooker for preparation of shaped foods of rice in a microwave range is made of microwave permeable synthetic resin such as polypropylene and internally provided with mutually separate confined spaces of a fixed capacity and adapted for accommodating rice with water. As the rice cooker containing uncooked rice with water is heated in the microwave range, compression acts on the boiled rice due to pressure contact of the boiled rice swelled and water with walls defining the spaces and the boiled water is automatically shaped in the spaces. Absence of direct contact of the rice with user"s hand during the process enables preparation of shaped foods of rice such as rice balls without any keen pain and blemish on the hands.

U.S. Pat. No. 5,229,563 discloses a pressure cooker and a process for making the same, wherein the pressure cooker includes a pressure container for accommodating food to be cooked, a cover for covering the container in an air-tight manner, a pressure control device for adjusting the internal pressure in the container. The container or the cover or both are partly or wholly made of a composite resin consisting essentially of polyphenylene sulfide resin and 30 wt. % to 50 wt. % glass fiber.

U.S. Pat. No. 5,310,981 discloses a microwave cooker capable of cooking an assortment of foods by a variety of methods while maintaining constant pressure.

This pressure cooker boils and steams foods continuously without pressure build up and without the need to shut off the microwave oven. Food spattering and spillage are prevented by a unique internal baffle rib design and a mechanism that releaseably locks the top cover. The top cover and inner cover of the pressure cooker have the same outer diameter and each have a plurality of vent holes or apertures. Both the top cover and inner cover are positioned within container and each have a skirted edge. The skirted edges form an enclosure within the container member, specifically designed to obstruct and contain escaping food particles.

Application no. 46/CHE/2010 of the applicant itself provides a unique pressure microwave cooker but with a lock means which is different from the existing invention. DISADVANTAGES OF RELATED ART

In many of the prior art, the pressure cookers comprising container and cover that have been constructed to allow operation of cooker i.e. attempting to cook without built in features for confirming to the user himself that the closing the cooker cover over the body of the cooker is proper and complete. Similarly in the prior art, the pressure cookers do not provide for built in features on the cooker for confirming to the user himself the suitability of or attempting to open when there is a pressure buildup inside etc. Further many attempts have been made in prior art to achieve an efficient pressure cooking system, but still all suffer from drawbacks of not achieving a very safe operating system, as the focus is generally on the efficiency in cooking or on fuel saving or on cooking time.

Further most of the cookers do not give attention to the issue of actually controlling the opening and closing of such cookers in a very reliably and very safe manner. OBJECT OF THE INVENTION

The primary object of the present invention is to provide a most reliable and safer lock system pressure cooker, comprising of sub-assemblies, all of which are designed to be compatible with corresponding energy and provided with all required safety features for cooking taking into account many typical mistakes that may be made by an user during using the cooker.

Further, the object of the invention is to provide pressure cooker mounted with safety locking devices prescribed in appropriate standards and having a fool proof locking means, thus eliminating the mistakes that may be made by an user during using the cooker.

It is another object of the invention to provide a lock means for the cooker which shall prevent erroneous closing and/or opening of the cooker thereby ensuring safe operation condition at all times.

It is another object of the invention to provide a simple, attractive and light weight pressure cooker in which all parts and subassemblies may be made up of materials that is compatible with microwave oven including the referred lock means.

It is another object of the invention to provide a simple, attractive and light weight pressure cooker in which all parts and subassemblies may be made up of either above referred lock or metal that is compatible with the corresponding used oven including the referred lock means. Both plastic and metal can be used for metal cookers.

It is another object of the invention to provide a pressure cooker with an improved pressure responsive locking device made of elastomeric material or of any suitable metallic material. It is attempted herein to provide a pressure cooker with an improved composite visual pressure indicating cum lock device made of corresponding material including the use of elastomeric material or metal or combination thereof for indicating the pressure that is developed inside the cooker. Yet another feature in the present invention is that it is provided with a specially designed visual pressure indicator cum lock means which is essentially capable of ensuring that when the cooker is under pressure the cover removal is not operable by user and further also ensures proper closure of the cooker prior to commencing the pressure buildup inside the cooker and additionally performs as a visual pressure indicator.

It is further object of the invention to provide an effective, easy and composite means of releasing the pressure quickly, if so desired by the user by pushing down the visual pressure indicator.

According to the present invention, the pressure cooker may be a conventional pressure cooker or a microwave pressure cooker. If it is microwave pressure cooker then it needs to be made-up of microwave compatible material like polypropylene with the use of silicone for sealing and safety devices and otherwise, the same or a metallic lock means may be designed.

In this present invention, the pressure cooker works on the principle of normal pressure cooking like in a conventional cooker used on a gas stove, induction, microwave oven etc. so that the cooking time is less compared to time taken by any non pressure cooking.

According to the present invention, the pressure cooker has specially designed lock device. This may be made with metal or microwave compatible materials as detailed above. BRIEF DESCRIPTION OF DRAWINGS

The Multifunction Safety Lock (MFSL) in FIG. 2 shows the position of locking lever when the cooker is under pressure. Under pressure the visual pressure indicator (rod) is extended above the top surface of the safety lock cover. The lock position of the lock means in the extended state will not allow the cooker to be opened until the visual pressure indicator drops.

The Multifunction Safety Lock in FIG. 1 shows the position of lock means, when the cooker is not under pressure. The visual pressure indicator (rod) is down and the lock position of the lock means in the retract state allows the cooker to be opened.

Safety lock cover means cover in the multifunction safety lock, which can be removed to clean. The cover needs to be replaced after cleaning. The cover needs to be in place when cooker is used for cooking. Cooking without the cover can scald the finger when the user attempts to press the visual pressure indicator (the rod) to release the pressure.

The invention in one aspect discloses a Multifunction Safety lock means which is a pressure indicator cum lock for a pressure cooker. The Multifunction Safety lock means is a pressure response type body. It has a pressure monitoring means comprising of a moving rod between a first state and second state. A silicone sealing washer is mounted on the rod. The rod along with this washer combinedly is mounted freely across a hole formed on the cover of the cooker with the washer positioned underneath the cover. This rod and washer move upward under increasing pressure to lift the rod from the first state and the washer towards the underside of the cover thereby pushing sealingly the circular washer until positioned against the underside of the cover to seal the said hole and simultaneously the rod also extending upwardly above the top surface of the cover to reach the second state of the rod.

Further the rod moves downward under decreasing pressure to drop from the second state and the washer moves downward away from the underside of the cover thereby unsealingly away from the underside of the cover to unseal the said hole on the cover and the rod dropping downwardly until rod head seated against the top surface of the cover to reset into the first state of the rod. The first state of the rod is indicative of zero internal pressure. The second state of the rod is indicative of operating internal pressure of the cooker. It also has a locking means of push rod type operably associated with the pressure monitoring means comprising of first end connected to the top end of the rod and the second end terminating near the peripheral edge of the cover and passing through a hole formed on the peripheral edge of the cover. It is arranged such that the second end of lock means is responsive and representative of the state of the rod with two positions which are extended state and retract state of the lock means corresponding to second state and first state of the rod of pressure monitoring means. Like in any conventional cooker a plurality of locking lugs on the base container associated with matching locking lugs on the cover but has one set of matching locking lugs of the container adapted to engage with the said locking means on the cover.

The said arrangement is characterized in ordinarily securely locking the cover with the container when the said specific set of matching locking lug of the container is engaged with the said locking means and the internal pressure builds up a predetermined value and the locking rod is in extended state thereby becoming visible above the cover. Further it can ordinarily securely unlock the cover from the container when the internal pressure is released entirely and the locking rod is in retract state. It also ordinarily prevents pressure buildup if the said specific set of matching locking lug of the container is not engaged with the said locking means on the cover under partially closed condition the push rod of locking means is positioned against the lug of the container and is therefore prevented from engaging properly and hence prevents further pressure buildup. Further intentional manual downward push motion of the rod of the lock means will allow rapid release of the buildup pressure, which feature is desired very often by user.

In another aspect the invention relates to a pressure cooker with a Multifunction Safety lock means for securely locking the container with the cover prior to cooking and the said lock means which acts as a pressure indicator cum lock means with pressure response type body as described above.