How to choose stove-top pressure cooker?
How does a pressure cooker work? Physics
When a pot of water is heated, the boiling temperature of water remains at 212°F in equilibrium with atmospheric pressure irrespective of how much heat is applied. If pot is sealed with a lid, to prevent the steam from escaping, the steam creates pressure raising the boiling point. Higher the temperature, quicker the food cooks. The cooking time depends chemical and physical makeup of the food. Steam is a better conductor of heat than air, that's why the food cooks faster in pressure cooker than in an oven at the same temperature. The cooking time depends on pressure differential to permit penetration, temperature, and the steam.
In general, cooking rate doubles for every 7.5 psi increase in pressure. At 15 psi, cooking rate quadruples decreasing cooking time to one fourth. At sea level, the pressure is 0 psi. For each pound of increase in pressure, the boiling point is raised by 3°F. The PC incorporate a steam release/heat reduction method to maintain maximum of 15 psi. At 15 psi, the boiling point is raised by 3x15 or 45°F, or the food will cook at 4 times faster, or decrease cooking time to about one fourth.
How many types of Pressure Cookers are available?
Three generations of pressure cookers have evolved over time and in use today. Click here to see Pressure Cooker Time-line
1st Generation: The lid of cooker employs a rubber seal gasket to make an air-tight fit, a rubber plug that bows off under extreme pressure, and a steam vent that is covered with a weight. When the pressure exceeds 15 psi, the weight is lifted to release some pressure. The heat is turned down to let the steam vent about once a minute maintaining 15 psi. The weight appears to jiggle and normally called a a 'jiggle-top'.
In United States, leading Manufacture is Presto.
2nd Generation: In 1949, Kuhn-Rikon (Switzerland) replaced the 'steam vent and jiggle-top' with a precision spring inside the valve and a pin. The pin is pressed to set a given pressure, it pops up when the preset pressure has reached. The pop-up pin is also used to release pressure quickly. In some of the models you can set it two selectable pressures 15 psi and 8 psi. The spring-valve system is basically a closed loop system wasting very little water as steam, it is quieter and holds heat longer. The jiggle-top PC can lose almost ¾ cup of water in five minutes to maintain 15 psi. Saving loss of water through steam results in more concentrated flavors.
The Kuhn-Rikon pressure cooker was introduced in USA during early 1990s.
High end second generation pressure cookers are: Kuhn-Rikon (Switzerland), Fissler (Germany), B/R/K (Germany), Fagor (Spain, China), Magefesa (Spain)
3rd Generation: These cookers are based on Electric Rice Cookers, the heating element in the Rice cooker was controlled by a microprocessor based fuzzy logic. After the rice has soaked up the water, the temperature suddenly jumps above 212° F. When the logic detects this rise in temperature, the cooker is shut off. For pressure cookers, the fuzzy logic will let the pressure rise up to 257° F, and then maintain it for a set time period. The lid used a modified version of spring-valve and pin system. This allowed more flexibility for un-attended operation.
No Electric Pressure Cookers are manufactured in Europe or USA. Midea (China) is the world's largest manufacturer of Electric Pressure Cookers, IP-LUX60 is their best current model.
Pressure cookers are real time savers for Indian cooking, specially the whole beans such as: Cholay (Garbanzo) , Rajma (Red kidney beans), Mah (Black beans); Chicken, Lamb, and Goat curry.
The Material (Cooking Pot)
The pressure cookers cooking pot is made of either Aluminum or Stainless steel. The Aluminum is reactive to acids in the food, which may discolor or even pit the pressure cooker. Also, it has been found that cooking in bare Aluminum may contribute to Alzheimer's disease. I don't recommend using Aluminum pressure cookers.
The stainless steel is not reactive to foods. I recommend using 18/10 stainless steel pot with a heavy bottom (A layer of aluminum sandwiched two outer layers of stainless steel). Heavy bottom provides uniform heating to sauté the Masala and brown Chicken or Lamb before cooking under pressure. How to choose Stainless steel Flatware and cookware
The Size (Capacity)
Most common sizes are 4, 6, and 8 quarts. This is misleading, one third of the cooking pot must be empty for steam to exert pressure. Legumes/beans and Rice expand to double in volume after cooked, it reduces the usable portion to 50% for raw materials including water. I recommend a minimum of 6 quarts, preferably an eight quarts size. Large size makes sauté and browning easier. You can even cook whole chicken
There are many types of pressure regulators. Some jiggle, constantly, others do not. I like the ones that jiggle. The constant noise keeps me aware that something is cooking. Both types work well.
Some of the regulators have built in quick pressure release option.
Some of the pressure cookers are fixed to maintain 15 pounds of pressure. Others, vary from 8 to 15 pounds. 15 pounds is well accepted standard .
Make sure the regulator is detachable/removable. This allows you ensure that the vent pipe is not clogged.
The pressure cooker should have two handles, the main handle and on the opposite side a helper handle. After the cooking time is up, you may want to pick up the pressure cooker and kill the pressure quickly by putting it under running water.
Make sure the pressure cooker is UL listed. It ensures that the cover, the construction and design are safe.
6 to 8 quart stainless steel (18/10) pressure cooker with the heavy bottom construction (a layer of aluminum sandwiched in between layers of stainless steel) with a UL listing sticker.
At sea level, water boils at 212º F. At air pressure of 15 pounds per square inch, the boiling point for water becomes 257º F, that is why the food cooks faster.
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