The Physics
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Pressure in a Pressure Cooker

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Nave, R. Pressure Cooker. HyperPhysics Concepts. "It is typical for the pressure of venting to be about 15 pounds per square inch above atmospheric pressure" 1.02 atm
Berendsohn, Roy. T-Fal Revisits Pressure Cooker. Popular Mechanics. (August 2002). "One is a low pressure setting of 10 pounds per square inch (psi) for vegetables and delicate foods and the other is a 13-psi setting for meat and defrosting." 0.68–0.88 atm
Phelan A.M., Louis. Pressure Cooker With Vertically Shiftable Cover and Exhaust. U.S. Patent 2,942,753. 28 June 1960. "Cooking devices of this type are large, often being on the order of 16 inches in diameter, and as a superatmospheric pressure in the vessel of 35 p.s.i. is commonplace, a considerable force acts on the cover tending to open during the cooking operation." 2.38 atm
Recipes are Designed for 15psi. Miss Vickie's Guide to Modern Pressure Cookery. "Most pressure cooker recipes are made to cook at the standard of 15psi, in fact this setting is so common that most recipes don't even need to mention it. This setting is the standard as determined by the USDA way back in 1917 when all pressure cookers had just that one 15psi setting. That pressure setting still remains as the standard today. 1.02 atm
"Others, mostly of European manufacture that state they cook at high pressure in fact only reach 10psi (WMF brand from Germany), the Chef's Design pressure cooker is limited to 11.6psi, or the 13psi T-Fal which will only attain 11psi. Also Fagor's Magic Pressure Fryers only go to 10psi, but that is a safety factor when cooking with so much oil." 0.68–0.88 atm

If you were born anytime in the 90's chances are you probably have never seen popcorn made in the house without the use of a microwave oven. Well, back in the day before microwaves became a fixture in American homes, pressure cookers were put into good use. Pressure cookers can be used to make anything from baked beans to steamed vegetables and are still in use today.

Although pressure cookers look like your normal cooking pot, they are very different as their lids are intricate in design. The lid works to seal the pot to build up the pressure inside. This is usually done by boiling liquid and keeping the steam trapped. As the pressure inside the pot rises so does the boiling point, which results in higher cooking temperatures. The main advantage of this process is reduced cooking times.

In the US, the pressure of the trapped steam is measured in pound of force per square inch or psi. One psi is approximately equal to 6895 pascals or 0.06804 atmospheres (atm).

Based on the standards put in place by the USDA in the early 20th century when pressure cookers were first invented, most pressure cookers made in the U.S. were set to run at 15 psi which is equal to 103,000 pascals or 1.02 atm. European pressure cooker makers like T-Fal generally manufacture their cookers to be set between 0.68-0.88 atm (11-13 psi). Despite the differences, most pressure cooking recipes are designed for 15 psi models.

Islam Soliman -- 2008