How do pressure cookers work

The first patent for a pressure cooker was granted to Georg Gutbrod in Spain in , but it wasn't until Alfred Vischler presented his pressure cooker at the World's Fair that commercial production began for home use. Since this time pressure cookers have been prized for their time and energy-saving qualities.

Boiling and steaming are already great cooking methods because water is a much better conductor of heat than air. To demonstrate this, think about how you can easily place your hand in a F oven without it burning, but if you were to place your hand in a pot of boiling water F , you would burn immediately.

This is because water or steam conducts energy heat very well, whereas air does not. The limiting factor of cooking with water or steam is the maximum temperature. Water boils at F, at which point it turns into steam. Once the water reaches F and begins to boil, the temperature does not increase any further until all of the water has been converted to steam.

The boiling water and steam remain at F, regardless of how long it boils, limiting the rate at which it can cook food. The only way to increase the temperature of boiling water as it converts to steam is to increase the surrounding pressure. This can be achieved by trapping the steam in an enclosed space. As water transforms into steam, it expands in volume.

If the volume is not allowed to increase, the pressure and therefore temperature , will increase. Pressure cookers trap steam in an enclosed space through an air-tight, locking lid. If a well sealed cover is put on the pot to trap the steam that would otherwise evaporate, the pressure inside the pot goes up. Look for 15 pounds psi. Cooking temperatures at different pressures: the higher the pressure, the shorter the cooking time.

The easy-to-use spring-type pressure regulator on a modern pressure cooker. The pressure regulator controls the pressure inside the pot. The higher the pressure of the pressure cooker, the shorter the cooking time. For example, when the pressure selector dial on a modern pressure cooker, such as a Fagor Duo new generation pressure cooker , is turned to its High setting, it is safely under a pressure of 15 pounds per square inch psi.

To put 15 pounds of pressure in perspective, it is less than half the pressure of the air found in car tires, so is not very much; but still, the pressure inside the pressure cooker is still able to significantly shorten the cooking time of food. The steam pressure inside the pressure cooker cooks food much, much more rapidly than just boiling or baking food.

Unlike microwave cooking, pressure-cooked foods become moist and succulent with an intense intermingling of flavours. Pressure-cooked foods retain much more of their vitamins and nutrients than boiled or commercially processed foods do.

For safety, the lid is locked on while at full pressure, and you have to release the pressure before you can lift the lid. This can lengthen the total cooking time if you then have to put the lid back on and return the cooker to full pressure. Finally, food can easily overcook if left in the pressure cooker for just a few minutes too long. What are the best foods to cook in a pressure cooker and why? Pressure cooking is a moist-heat cooking method, so foods that taste good boiled, braised, or simmered work best.

Good options include soups, stews, and stocks; dried beans, whole grains, risotto, polenta, and grits; dense vegetables like beets and carrots; and meats you might otherwise consider for braising, like beef chuck, pork shoulder, or chicken parts.

Pressure cooking these foods causes their proteins to denature, their starches to gelatinize, and their fibers to soften in about one-third the time they would under normal atmospheric pressure. For example, hard dried beans, like chickpeas, which normally take more than an hour to cook, can be pressure cooked in about 20 minutes.

A full-flavored beef stock that would normally simmer for the better part of a day can be pressure cooked in an hour, and risotto is ready in about 10 minutes. How you release the pressure plays an important role in the cooking process. There are three basic pressure-release methods: natural release, achieved by turning off the heat and letting the pressure drop naturally; running the pot under cold water; and quick release, which means manually opening the release valve on your cooker.

Natural release takes 5 to 20 minutes, depending on the quantity and density of the ingredients; it works best for foods like braised meats and dried beans, which benefit from a resting period after cooking and tend to break apart during rapid depressurization. Both the cold water and quick release methods rapidly depressurize the cooker and are ideal for most vegetables and grains, which can easily overcook.

Reliable recipes are key to good pressure cooking, since accurate timing is critical to preventing overcooking or undercooking. To be on the safe side, slightly underestimate the total cooking time. If you release the pressure to check on the food and find that it needs more time, simply put on the lid and simmer for a few minutes or lock the lid back in place and return the cooker to full pressure.

Pressure Cookers Are Now Fail-Safe In the s, pressure cookers were commonplace in American kitchens, but stories of cookers exploding because of improper sealing scared people off. By the s, pressure cooking in the United States largely became a thing of the past, thanks to frozen dinners and other convenient meal solutions. In Europe, where such items were not as popular, the pressure cooker remained a preferred way to speed up mealtime. All pressure cookers are now fail-safe. They come equipped with a backup vent or an overpressure plug that releases excess pressure in case you forget to turn down the heat after the pot reaches full pressure, or if the main vent becomes clogged with food during cooking.

An expanding rubber gasket sitting inside the lid also makes it impossible to unlock and remove the lid until the pressure inside the cooker has been released. Periodically, make sure the main vent is clear by running warm water through it, and check to see that the overpressure plug or back-up vent is clear.

In first generations we had a boiling point of water below 80 deg C for cooking and below 50 deg C for canning. Below are general instruction how to use a first generation pressure canner. Open petcock by turning petcock knob counter-clockwise. Turn heat on high.

When cooking, close the petcock when a continuous flow of steam issues from it. This will be about two to three minutes after the first wisps of steam begin to issue from the petcock.

When canning, the steam is allowed to flow for seven to ten minutes before the petcock is closed. In step 4 we are producing the nessecary vacuum in order to lower the boiling point of water. For canning the time is bigger multiply by 2 or 3 so we have boiling points below 50 deg C. The pressure cooks foods rapidly with live steam at temperatures from 15 to 40 degrees above the boiling point of water. Furthermore, foods are not immersed in water and cooking is done in the absence of air, since the air is Automatically in Second generation pots expelled from the pan when cooking begins.