Because there is less atmospheric pressure at high altitudes and the air is thinner, water boils at a lower temperature. This means that it can be impossible to cook food at the correct temperature and that the water tends to evaporate very quickly.
Whether you live at a high altitude or sea level, the boiling point of a pressure cooker remains fairly constant. It means that you can prepare beans without presoaking, roast cuts of meat, create casseroles and make anything you want in a fraction of the time of conventional cooking.
Although steam engines and machinery are now largely redundant, it is a marvel that the pressure cooker which was developed using the same technology in the 17th century is still in daily use today. High pressure limits boiling, and permits cooking temperatures well above 100 °C (212 °F) to be reached.
The pressure cooker was invented in the seventeenth century by the physicist Denis Pain, and works by expelling air from the vessel, and trapping the steam produced from the boiling liquid inside. This raises the internal pressures and permits high cooking temperatures.
According to New York Times Magazine, 37% of U.S. households owned at least one pressure cooker in 1950. 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.
A six-quart pressure cooker manufactured by Archibald Kendrick & Sons in England, circa 1890In 1679, French physicist Denis Pain, better known for his studies on steam, invented the steam digester in an attempt to reduce the cooking time of food. His airtight cooker used steam pressure to raise the water's boiling point, thus cooking food more quickly.
In 1681 Pain presented his invention to the Royal Society of London as a scientific study; he was later elected as a member. It could cook rice, pulses and vegetables in steam, very fast and was used by bachelors.
In 1918, Spain granted a patent for the pressure cooker to José Alex Martínez from Zaragoza. Martínez named it the Ella express, literally “express cooking pot”, under patent number 71143 in the Bolton Official de la Provided Industrial.
In 1924, the first pressure-cooking pot recipe book was published, written by José Alex and titled “360 formulas DE Corina Para guitar con la 'Ella express'”, or 360 recipes for cooking with a pressure cooker. Mountaineers attempting to climb Mount Everest took it along with them to cook in higher altitudes.
In 1938, Alfred Fischer presented his invention, the Flex-Seal Speed Cooker, in New York City. Fischer's pressure cooker was the first designed for home use, and its success led to competition among American and European manufacturers.
Some people consider them loud because the valve rattles as excess steam is released. Others use a dial that the operator can advance by a few clicks (which alters the spring tension) to change the pressure setting or release pressure ; these release steam during operation (venting).
Depending on cooking control capability, there are three generations of electric pressure cookers: Delayed cooking becomes possible and the controller shows a countdown timer when working pressure is reached.
The second configuration consists of a completely removable air fryer lid, with a protective pad for storage. This is the configuration used by most other pressure cooker manufacturers, including Instant Pot.
Once the desired pressure and temperature are reached, the heat can be lowered somewhat to minimize excess release of steam, saving energy. Some recipes require browning to develop flavors during roasting or frying.
Browning occurs via the Millard reaction, under temperatures higher than the roughly 120 °C (248 °F) achieved in pressure-cooking. A pressure cooker can be used to compensate for lower atmospheric pressure at high elevations.
Without the use of a pressure cooker, boiled foods may be undercooked, as described in Charles Darwin's The Voyage of the Beagle (chapter XV, March 20, 1835): Having crossed the Sequences , we descended into a mountainous country, intermediate between the two main ranges, and then took up our quarters for the night.
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 Pain's digester. The pot was left on the fire all night, and next morning it was boiled again, but yet the potatoes were not cooked.
At higher altitudes, the boiling point of liquid is somewhat lower than it would be at sea level. Lightweight pressure cookers as small as 1.5 liters (0.40 US gal) weighing 1.28 kilograms (2.8 lb) are available for mountain climbers.
A Korean study of antitoxins in rice (associated with Aspergillus fungus) showed that pressure-cooking was capable of reducing antitoxin concentrations to 32% of the amount in the uncooked rice, compared to 77% from ordinary 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.
Pressure cookers are typically made of aluminum (aluminum) 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. 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. A common modern design, it has easily implemented locking features that prevent the removal of the lid while under pressure.
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 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.
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. Because of the forces that pressure cookers must withstand, they are usually heavier than conventional pots of similar size.
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. 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.
These safety devices usually require replacement when activated by excess pressure. This release of excess pressure is forceful and sufficient to extinguish the flame of a gas stove.
Maximum fill levels The recommended maximum fill levels of food/liquid avoids blockage of the steam valve or developing excess pressure : two-thirds full of solid food, half full for liquids and foods that foam and froth (e.g., rice, pasta); adding a tablespoon of cooking oil minimizes foaming., and no more than one-third full for pulses (e.g., lentils). Thick sauces do not contain enough liquid to vaporize and create pressure, so they usually burn onto the interior base of the pressure cooker after prolonged heating.
Food is placed inside the pressure cooker with a small amount of water or other liquid such as stock. The lid is closed, the pressure setting is chosen and the pressure cooker is placed on a stove on the highest heat (less than high for induction cooking to allow air to be vented).
Recipes for foods using raising agents such as steamed puddings call for gentle pre-reading, without pressure, in order to activate the raising agents prior to cooking and achieve a light, fluffy texture. It takes several minutes for the pressure cooker to reach the selected pressure level.
A common mistake is for the user to start timing when a colored pop-up indicator rises, which happens when there is the slightest increase in pressure, instead of waiting for the cooker to reach its selected pressure level. This pop-up indicator often acts as an interlock, preventing the lid from being opened while there is internal pressure.
With first generation designs, the pressure regulator weight begins levitating above its nozzle, allowing excess steam to escape. Steam has a much higher specific heat than air, and the presence of steam rather than air inside the pressure cooker is how it is able to transfer sufficient heat into the parts of the food that are not submerged in liquid, such as a pot roast.
This is why a pressure cooker takes about 10 minutes to reach pressure. The newer generation pressure cookers, which have no weights, automatically expel air from inside for several minutes before a colored pop-up indicator pin rises to seal the lid airtight; pressure then builds in the now airtight cooker.
If the pressure cooker is already hot or a stove top pressure cooker is placed on a very strong heat source, such as induction on too high a setting, the lid can seal airtight too quickly before the air inside has been removed. In these situations, a slightly lower heat setting can be used to allow the water to boil slower in order to vent the air.
The containers can be used for cooking foods that are prone to burning on the base of the pressure cooker. Cooking time is longer when using covered containers because the food is not in direct contact with the steam.
The flavor of some foods, such as meat and onions, can be improved by gently cooking with a little preheated 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 “sauté” or “brown” option for frying ingredients.
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.
It involves the quick release of vapor by gradually lifting (or removing) the valve, pushing a button, or turning a dial. 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.
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.
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.
Cold water quick release This method is the fastest way of releasing pressure with portable pressure cookers, but can be dangerous if performed incorrectly. 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 underwater, 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. 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.
The standard cooking pressure of 15 psi gauge was determined by the United States Department of Agriculture in 1917. The actual cooking time also depends on the pressure release method used after timing (see Pressure release methods for details) and the thickness and density of the food, since thicker (and denser) foods take longer to cook.
Frozen foods need extra cooking time to allow for thawing. Some recipes may require cooking at lower than 1 bar/15 psi (gauge) e.g. fresh vegetables, as these can easily overcook.
Food is cooked more quickly in a pressure cooker because at the higher pressure (1 bar/15 psi), the boiling point of water rises from 100 °C (212 °F) to 121 °C (250 °F). The hotter steam is able to transmit its thermal energy to the food at around 4 times the rate of conventional boiling.
Pressure-cooking requires much less water than conventional boiling, so food can be ready sooner. Since less water or liquid has to be heated, the food reaches its cooking temperature faster.
Pressure cookers can use much less liquid than the amount required for boiling or steaming in an ordinary saucepan. The minimum quantity of water or liquid used in the recipe to keep the pressure cooker filled with steam is sufficient.
Manufacturers provide steamer baskets to allow more foods to be cooked together inside the pressure cooker. Because of this enhanced germ killing ability, a pressure cooker can be used as an effective sterilizer for jam pots, glass baby bottles, or for water while camping.
In fact, the autoclave, used in hospitals to sterilize surgical instruments, is really just a more precise and technical version of the ordinary pressure cooker. Pressure cookers are considerably more expensive than conventional saucepans of the same size.
Gasket The additional gasket (sealing ring) requires special care when cleaning (e.g., not washed with kitchen knives), unlike a standard lid for a saucepan. The gasket/sealing ring needs 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. 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.
With a conventional saucepan, this can be done in a matter of seconds by visually inspecting the food. As a result, accurate timing is essential for the recipe e.g. with an audible timer.
A minimum quantity of liquid is required to create and maintain pressure, as indicated in the manufacturer's instruction manual. This is not desirable for food requiring much less liquid, but recipes and books for pressure cookers take this into account.
Nonetheless, small, lightweight pressure cookers are available for mountain climbers (see High altitudes) . The appliance has been adapted as a crude type of bomb, which has been used in terrorist attacks.
An autoclave is a type of pressure cooker used by laboratories and hospitals to sterilize equipment. Their main function is as an enhanced oven or broiler for meat and poultry, avoiding drying.
“A Pot With Benefits--How the pressure cooker fell out of favor, and why it's time to bring it back”. “360 formulas DE Corina Para guitar con la “Ella express”.
“Effect of home processing on ascorbic acid and beta-carotene content of spinach (Spinacia operatic) and amaranth (Amaranths tricolor) leaves”. ^ “EXCLUSIVE OFFER: Ninja Food TenderCrisp Pressure Cooker and Air Fryer”.