How it works
Technically, a pressure cooker is a stainless steel, or aluminum, pan that can be used on a flame or electric cooktop. It has a top that locks closed with a couple of valves on the top. While liquid boils and turns to vapor inside, the pressure rises and a valve on top (either spring-loaded or jiggly) opens automatically to let out excess vapor and maintain the pressure at about 13-15 psi – some pans give you the option to regulate the pressure.
Also, on the top of the pan there is a rubber or silicone safety valve that will pop out and release pressure in case the vapor valve were to clog (to avoid "explosions") and a safety latch to keep you from opening the pan while the pressure is still high inside (to avoid boiling liquid from spraying you). The bottom part of the pressure cooker can be used as a normal pan when you are not pressure cooking.
How it saves energy
It takes almost 90% more energy to cook at a rolling boil (HIGH heat) in a regular pan for an hour versus twenty minutes (LOW heat) in a pressure cooker- and the results are the same! A Vegetarian Chili which simmers for 11/2 to 2 hours in a regular pan cooks in just 30 minutes in a pressure cooker on low.
How?!?
First, the temperature inside pressure cooker can rise to 250°F/121°C. This is a big deal because boiling water and its vapor can never go over 212°F/100°C. The higher temperature means that the cooking time is reduced to one third. Second, the sealed top of the pressure cooker allows for very little heat to escape, so once the pressure is reached (and the contents are boiling inside) the heat can be reduced to minimum.
The energy efficiency of this pan is the reason why pressure cookers are so popular in Italy and other countries, like India and Cuba, where energy for cooking is expensive! Almost every household in Italy has a pressure cooker and new brides usually receive their first as a wedding gifts — old broads can pick one up at the supermarket—as I did.
What it can cook
You can use a pressure cooker to cook vegetables, meat, fruits, fish, grains and it is famous for how quickly it can cook beans! A pressure cooker will let you cook any of the above in the following ways:
• Brown – this is the first step in many recipes, like risotto, and can be done before or the lid is placed, or after it is removed.
• Boil – just add enough water to cover the food by half.
• Steam - insert the accessory, or a metal-foldable steaming basket with ½” of water.
• Braise – brown the food in the pan, and then add cooking liquid (wine, milk, broth, water).
• Stew - throw everything in and close the top.
• Roast – place the meat and vegetables inside with just 1-2 cups of cooking liquid.
• Reduce – after the lid is removed, cook on high flame to reduce liquids if desired.
• Bain Marie (Water Bath) – place a heat-resistant bowl (ceramic, pyrex, stainless steel, silicone ), covered in aluminum foil on steamer basket inside pressure cooker with 1 cup of water on the bottom.
• Cooking Rice - add the right proportion of rice & liquid and, for most rices, bring to pressure and then turn off the heat. Let pressure come down naturally for about 10 minutes before opening.
• Canning - You can do a hot-water bath "processing" of jams and jellies without pressure.
• Pressure Canning -steam the canning jars on the steamer basket and open with the natural method.
• Extracting Juice - place the fruit in a steamer basket with a container underneath.
How it's healthier
Keep your vitamins… don’t boil or evaporate them away!
Vegetables cooked under pressure lose very few vitamins, minerals, taste and color compared to boiling. These guys stay in the food because the sealed top minimizes evaporation, the pan requires less cooking liquid to cook and expels all oxygen during pressure (no oxidation)!
In fact, when adapting your recipes to the pressure cooker you only need to add a fraction of the liquid and salt.