PRESSURE COOKING

a pressure cooker

'Pressure cooking' is a method of cooking in a sealed vessel that does not permit air or liquids to escape below a preset pressure. Because water's boiling point increases as the pressure increases, the pressure built up inside the cooker allows the liquid in the pot to rise to a temperature higher than 100 °C (212 °F) before boiling.
Pressure cookers may be referred to by several other names. An early pressure cooker, called a ''steam digester,'' was invented by Denis Papin, a French physicist, in 1679. Large volume pressure cookers are often referred as pressure canners, due to their capacity to hold jars used in canning. A version of a pressure cooker used by laboratories and hospitals to sterilize materials is known as an autoclave. In the food industry, pressure cookers are often referred to as retorts.

Operation

Advantages

Safety features

Use at high altitudes

Use in food detoxification

Operation

Since pressure cooking depends on the pressure of steam, the process cannot easily be used for methods of cooking that produce fairly little steam, such as roasting, pan-frying or deep-frying. Most pressure cookers sold in the U.S. have an internal pressure setting of 15 psi, the standard determined by the USDA in 1917. At this pressure boost relative to sea-level atmospheric pressure, water boils at 125 °C (257 °F). The higher temperature causes the food to cook faster. Cooking times can be reduced by a factor of 70 percent. For example, shredded cabbage is cooked in one minute, fresh green beans in three minutes, small to medium-sized potatoes cook in five minutes (depending on thickness and type), and a whole "roast" chicken takes only twenty minutes. It is often used to simulate the effects of long braising or simmering in shorter periods of time. Some pressure cookers do not reach the standard 15 psi pressure and cooking times may need to be increased slightly to compensate.^[1]
The materials used for making cookers are generally aluminium and stainless steel. The former may be stamped and buffed or anodised, but this metal is unsuitable for the dishwasher. Expensive stainless steel pressure cookers are made with heavy, three-ply, or copper-clad bottoms for uniform heating. Most modern units are dishwasher safe, although some manufacturers may recommend washing by hand. A gasket forms an airtight seal which does not allow air or steam to escape between the pan and the lid, the only way the steam can escape is through a regulator on the lid when the pressure has built up (or if the regulator is blocked, through a safety valve). Sometimes the gasket is referred to as a sealing ring.

Advantages

★ Cooks foods much faster as compared to other methods.

★ Uses less fuel than boiling/steaming the same quantity in an ordinary pan, due to the shorter duration of fuel consumption.

★ Hygienic compared to open cooking in a pot or utensil. The food is cooked above the boiling point of water, killing more germs.

★ Nutrients of food are better retained in pressure cooking.

★ Easy to cook with in comparison to other modern gadgets.

★ Pressure cookers can be used in most of food styles, cooking styles, different recipes.

★ Easy to clean pressure cooker after cooking.

★ Allows higher quality cooking at high altitudes (see below section).

★ The pressure cooker pan can be used as an ordinary saucepan for cooking larger quantities of food.

★ Several foods can be cooked together in the pressure cooker. Besides saving fuel, this reduces the amount of washing up.

Safety features

Pressure cookers have a reputation as a dangerous method of cooking with the risk of explosion. Early pressure cookers equipped with only a primary safety valve were at risk of explosion if poorly maintained, allowing food residues to contaminate the release valve. Modern pressure cookers typically have two or three independent safety mechanisms, as well as some additional safety features required for UL approval or the equivalent in other countries, such as an interlock to prevent opening the lid while internal pressure exceeds atmospheric pressure.
Modern pressure cookers employ several safety features, such as a lid interlock and a gauge to indicate when the cooker is pressurized. The pressure cannot build up unless the lid is properly closed and locked in place.
A regulator releases steam when the pressure exceeds the designed pressure for the cooker; this usually takes the form of a weighted stopper, commonly called "the rocker," or "vent weight". This weighted stopper is lifted by the steam pressure, allowing excess pressure to escape. There is usually a backup pressure release mechanism (a safety valve of sorts) that may employ any of a number of different techniques to release pressure quickly if the primary pressure release mechanism fails (for example, if food jams the steam discharge path). One such method is in the form of a hole in the lid blocked by a plug of low melting-point alloy. If the internal temperature (and hence pressure) gets too high, the metal plug will melt, resulting in release of pressure. Another technique takes the form of a rubber grommet with a metal insert at the center. At a sufficiently high pressure, the grommet will distort and blow out of its mounting hole, rapidly releasing the pressure. A common safety feature is the design of the gasket, which expands and releases excess pressure downwards between the lid and the pan (if the pressure cooker is heated on a gas burner, this downward release of pressure can be strong enough to extinguish the gas flames). In some pressure cookers, excess pressure forces the pressure indicator above its housing which releases the pressure vertically upwards, to open the lid after this happens, one must allow the pressure cooker to cool down and then push the pressure indicator down before opening the lid in the usual manner.

Use at high altitudes

A pressure cooker is often used by mountain climbers to compensate for the low atmospheric pressure at a very high altitude. Under these circumstances water boils at temperatures significantly below 100 °C and without the use of a pressure cooker, may leave boiled foods undercooked, as described in Charles Darwin's ''Voyage of the Beagle'':

Use in food detoxification

Some food toxins can be reduced by pressure cooking. A Korean study of aflatoxins in rice (associated with Aspergillus fungus) showed that pressure cooking was capable of reducing aflatoxin concentrations to 12 to 22 percent of the level in the uncooked rice.^[2]