Basics on How a Pressure Cooker works

Commercial Pressure Cooker

What is a pressure cooker?
A pressure cooker is a normal pot, but it is airtight and reaches pressures higher than atmospheric pressure. Due to this particular characteristic the boiling point of water increases if the pressure is increased.

How a pressure cooker works
What is a pressure cooker used for?
With the pressure that is achieved, the boiling point of water also increases. In this way the hermetic seal of the pot achieves that the boiling temperature can rise above 100 °C, specifically 130 °C. The pressure cooker is therefore suitable for cooking at higher temperatures and in less time. It also has the advantage of cooking with the same effect as a stew or simmering.

How does a pressure cooker work?
A pressure cooker is a hermetically sealed pot, which raises the cooking temperature. At sea level the standard atmospheric pressure is known to be 1 atm and water boils at approximately 100 °C. In the case of a pressure cooker, cooking takes place at a pressure of approximately 3 atm absolute and water boils at about 130 °C. Therefore, a high temperature allows the food to cook in less time. It is worth noting that inside the pot the water will never boil, but it does increase in temperature.

The phenomenon described above is described by Gay Lussac’s Law, which was enunciated in the early 1800s. This law explains that the pressure of a fixed volume of gas is directly proportional to its temperature. In that sense, if the pressure increases, so does the temperature.

When the lid of the pressure cooker is closed most of the gas contained inside will be air and not water vapor, which is why the pressure inside is the sum of the pressure due to water vapor, where its amount is increasing due to evaporation as the temperature increases, and also to air, in that the partial pressure is responsible as the pot heats up inside and moves further away from saturation. In this way the boiling of the water inside is prevented.

As soon as the maximum pressure is reached by the pot, which is determined by the valve, it cannot be modified. If it is kept at high heat, cooking will be accelerated, but only the evaporation of water will increase, as well as the loss of steam through the valve.

Types of pressure cookers according to the material
Pressure cooker models vary due to the type of material from which they can be constructed. The following are the types of pressure cookers.

Steel cooker – These are made of stainless steel which allows these cookers to be durable, heat resistant and easy to clean. The only flaw is the weight of the pot because steel is a metal of high density.

Copper pots – Being thicker than steel pots, they are also more resistant. Being also easy to clean, the main characteristic of this type of pot is the capacity to distribute the heat uniformly to all the volume contained in the pot because copper is a great thermal conductor.

Aluminum cookware – Among the 4 types of cookware, this is the easiest to clean, the lightest, besides being able to heat up very fast and to cool down as well. Now, if you are looking for a cooker that has a long life span, this type of cooker would not be the right one.

Generations of pressure cookers
First generation pressure cooker
– It is also known as old type and they work with a moving valve or one that changes according to the pressure that is produced. That movement is a result of placing a weight over an orifice in a given section, which releases excess pressure if the inside of the vessel achieves a pressure determined by the valve. They are usually very noisy.

Second generation pressure cookers – Operate with a spring-loaded valve, which is almost always hidden from the user’s view. They are characterized by some pressure adjustments. In some cases they do not release steam and the indicator they have are certain marks that show the pressure level.

Third generation or electric pressure cooker – Developed in 1991. They incorporate an electric heat source that is automatically regulated so that the pressure is maintained. They include a spring-loaded valve. It is not a pot that can be opened by a quick release method with water. It must be used with caution if steam is released from the valve.

  • How do I use a pressure cooker?
  • Knowing the cooker – Make sure you already know the characteristics of the cooker so that you use it correctly and safely. Check that everything is in order with no cracks or dents.
  • Fill the pressure cooker – It should not exceed two thirds of its capacity because there must be room for the steam that will accumulate.
  • Prepare your food – According to the type of food to be cooked will be the amount of time, the fire level, among other details. Verify these characteristics for good cooking.
  • Remove the valve – Remove the safety valve or pressure regulator and close the lid properly.
  • Pressure – Wait for the pot to gain the proper pressure.
  • Reduce the heat – It has to be a lower level so that the pot continues to boil and does not emit the hissing sound.
  • Depressurize – When cooking is considered finished, turn off the heat and wait until the internal pressure of the pot is no longer there. Depressurization is important, so do not lift the lid of the pot, but wait until all pressure is released.
  • Remove the cooker – Once all the above steps have been taken you can remove the cooker and check the cooking of your food.
  • How to use a pressure cooker safely?
  • Check quantities – The pressure cooker cannot be filled with more than two-thirds of its capacity. There must also be enough liquid inside for the food to be prepared properly.
  • Open the cooker carefully – If it is in use there is heat and steam inside. Therefore, release the pressure first and then open the cooker.
  • Safety valves – Check and verify that they are clean and in good condition so that the steam is expelled correctly.
  • Temperature – Do not expose the cooker to sudden changes in temperature.
  • Detergent – For washing use common dishwashing detergent and avoid other kinds of cleaning products.

Advantages and disadvantages of the pressure cooker
The main advantages of the pressure cooker are:

It saves time because of its ability to reach pressures higher than atmospheric pressure, therefore, the boiling point of water is increased.
It is very safe if all the instructions for its use are followed.
The maintenance of a pressure cooker is simple. It consists of washing and checking its parts from time to time.
It allows the preparation of all types of ingredients, especially when they are cooked in water.
The disadvantages of the pressure cooker are:

It is essential that the person knows the correct way in which it should be used, because it could explode if it is not depressurized before opening, for example.
Sometimes it cannot work properly because it has not been sealed tightly.