A pressure cooker is a sealed vessel used for cooking food with the use of high pressure steam and water or a water-based liquid, in a process called pressure cooking. The high pressure limits boiling and permits cooking at higher temperatures, allowing food to be cooked faster than at normal pressure. The prototype of the modern pressure cooker was the steam digester invented in the seventeenth century by the physicist Denis Papin. It works by expelling air from the vessel and trapping steam produced from the boiling liquid. This is used to raise the internal pressure 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 as well as saving considerable energy. Almost any food that can be cooked in steam or water-based liquids can be cooked in a pressure cooker. Modern pressure cookers have many safety features to prevent the pressure cooker from reaching a pressure that could cause an explosion or other dangerous situations. After cooking, the steam pressure is lowered back to ambient atmospheric pressure so that the vessel can be opened. On all modern devices, a safety lock prevents opening while under pressure. According to The 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. However, third-generation pressure cookers have many more safety features and digital temperature control, do not vent steam during cooking, and are quieter and more efficient, and these conveniences have helped make pressure cooking more popular.
History
In 1679, French physicist Denis Papin, 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 Papin presented his invention to the Royal Society of London as a scientific study; he was later elected as a member. In 1864, Georg Gutbrod of Stuttgart began manufacturing pressure cookers made of tinned cast iron. Although the concept of cooking with pressurized steam had been known for two centuries, the term "pressure cooker" was not commonly used until the early 20th century. The earliest citation of the phrase given in the Oxford English Dictionary is from a Lincoln, Nebraska, newspaper in 1914. However, the Dictionary editors apparently overlooked or did not have access to certain Colorado newspapers from a few years earlier than that. As early as 1910, the inventor Zeno E. Crook founded a business called "The Pressure Cooker Company" in Denver, Colorado. Crook had developed an aluminum cooker of a size practical for home use, and soon began marketing it to communities in the high country of Colorado, where the device proved to be well suited for use in high-altitude cooking. In many of these communities, Crook's pressure cooker was hailed as a marvelous new invention, until 1918, when Popular Science Monthly broke the news that this "invention" was actually more than 200 years old. 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. In 1924, the first pressure cooking pot recipe book was published, written by José Alix and titled "360 fórmulas de cocina Para guisar con la 'olla expres'", or 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 at higher altitudes. In 1938, Alfred Vischer presented his invention, the Flex-Seal Speed Cooker, in New York City. Vischer's pressure cooker quickly gained popularity, and its success led to competition among American and European manufacturers. At the 1939 New York World's Fair, the National Pressure Cooker Company, later renamed National Presto Industries, introduced its own pressure cooker.
First generation Also known as "old type" pressure cookers, these operate with a weight-modified or "jiggler" valve, which releases pressure during operation. Some people consider them loud because the valve rattles as excess steam is released. Older pressure cookers typically offered only one pressure level, but from the 1960s onwards some allow the operator to change the weight of the valve, thus changing the pressure. 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.
Second generation These operate with a spring-loaded valve that is often hidden from view in a proprietary mechanism. This generation is characterized by two or more pressure settings. Some of these pressure cookers do not release any steam during operation (non-venting) and instead use a rising indicator with markings to show the pressure level. These only release steam when the pan is opened, or as a safety precaution if the heat source is not reduced enough when the pan reaches the required cooking pressure. 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).
Third generation "electric pressure cookers"
After the stove-top pressure cookers came the electric pressure cookers in 1991, called the "third generation" pressure cookers. 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. An electric pressure cooker integrates a timer. Depending on cooking control capability, there are three generations of electric pressure cookers:
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