The Pressure Cooker

Pressure Cooker, Photo by Bel

Published: 30th November 2006 

There's hardly another kitchen item which splits the 'chefs' into two factions in the way that the pressure cooker does. There are those who love it because of all its advantages. And those who loathe it because they've heard from a friend that the pressure cooker of her friend's aunt's cousin's daughter... exploded. There seems to be nothing in between. So here is a brief introduction to the tool in question.

History
The pressure cooker¹ was invented by the French physicist, mathematician and inventor Denis Papin in 1679. Rumour has it that his first pressure cooker exploded while being presented at the Royal Society in London in 1679, which inspired Papin to invent the safety valve. The diarist and horticulturist John Evelyn gives a very positive record from another presentation at the Royal Society three years later. However, it is said that when pressure cookers were first used, some people thought they were the result of witchcraft because of the incessant hissing from the valve. In Germany, the first pressure cookers were sold in 1927.
What is it and How Does it Work?
The pressure cooker is a hermetically-sealed pot that heats the water or other liquid to a temperature of about 120°C. This is a far higher temperature than you can reach by cooking in an ordinary pot, thus reducing the cooking time by a factor of three to four. The liquid starts boiling and some of it changes to steam, which causes a mixture of air and steam to be released via the safety valve. Once all the air is released, pressure² is built up in the pot. Once the correct amount of pressure is reached and the heat is turned down to a level where it maintains the wanted pressure level, no more steam will be released. If the pressure gets too high, the valve will release steam to prevent the pot from exploding. Modern pressure cookers have a back-up pressure release, which comes into action if the safety valve gets obstructed by the contents of the pot, such as soup or stew.
What Does it Look Like?
The pot looks very much like any other pot. It comes in different sizes and materials, from aluminium over stainless steel to enamel. The bottom is thicker than that of other pots. The secret is in the lid, which is usually fitted to the pot by a bayonet lock. It contains a rubber ring and at least one safety valve. The safety valve not only releases air and steam, but has an indicator³ which shows the built-up pressure. Usually, there are two pressure levels you can choose from — the first mark for foods that don't need much pressure, such as vegetables and fish; the second, more commonly used, for practically anything else, such as potatoes, curry or meat. Additional items that come with the cooker are: an adjustable steaming sieve for potatoes, vegetables and other food you don't want to boil in water, but steam gently; a similar device without the holes to cook food such as rice separated from the food below; and an instruction manual with recipes.
Benefits

• It saves time (see above).
• It saves energy.
• You don't have to stir the meal and can use the time to prepare the salad, do the laundry or check what's going on on h2g2.
• If you do everything according to the instructions, the meal doesn't burn.
• No food smells spread through kitchen and flat, and the kitchen doesn't get steamy.

How to Use

• Read and follow the instructions in the manual carefully!
• Ensure that the correct amount of some sort of liquid (as indicated in the recipe) is in the pot.
• Make sure that the brim of the pot and the lid are clean and that the rubber ring is correctly fitted to the lid.
• Close and fasten the lid and heat it on the highest setting.
• Turn the heat down shortly after the first ring on the safety device shows.
• Activate some sort of timer to let yourself know when the food is cooked.
• Switch the hot plate off and either put the pot on a cold surface to release the pressure, let cold water run over the lid (not recommended for liquid foods and/or enamelled pots) or take a wooden spoon at the 'wrong' end and press on the ring-marked spring with the end of the handle.
• Never try to open the lid while the pot is still under pressure!
• Make sure your hands, body or face are nowhere near the steam release, or you risk scalding yourself badly.
• Once all pressure is released, open the lid.
• Enjoy.

What Else do I Have to Consider?
Don't be afraid that the pressure cooker might explode; it is highly unlikely, especially if you take care to turn the heat down at the indicated pressure. Make sure that you clean the valve and the rubber ring thoroughly after every use. The rubber ring will be the first thing you'll have to change — a clear indication is if the pot releases steam and doesn't reach the expected pressure. Either write down the model and diameter of the rubber ring or take the old ring to the shop to ensure that you don't buy the wrong model and/or size. The same goes for the valve in the rare event it has to be changed. Don't let the noise of the released steam startle you; after all, it's still less noisy than the whistle of your kettle.

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¹ It was first known as 'Papin's digester', after its inventor, and later as a 'steam digester'.
² About 2.0 bar. This is very useful when trying to cook food at high altitudes, because the low air pressure causes water to boil at less than 100°C.
³ Often a spring marked with two rings.
 Written and researched by Bel, edited by echomikeromeo