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How does a Pressure Cooker work?

Physics | 9-12 yrs | Animation, Video

The sound of a pressure cooker may be startling, but it is a call to you that it is doing its job. Yes! Food will be served soon.

This nifty appliance cuts the amount of time it takes for food to cook. There are 2 very important things happening inside the chamber of a pressure cooker. Let’s break down that process to understand it all—


A combination of steam and pressure make the pressure cooker this efficient kitchen delight. The two work together to cook things in no time.

One of the reasons we use water to cook food is because it is a better conductor of heat than air is. You can raise the temperature of water to transfer its energy to the water in food. Basically— cooking it.

The boiling point of water is 100°C, but did you know that this is true only under normal atmospheric conditions? This means that if you were trying light a fire under a pot of water on Mt. Everest, the water would begin to boil once it reaches 71°C, because there is less pressure 8,848m above sea level.

A pressure cooker does the opposite of what Mt. Everest does- it increases the pressure so that the water will come to a boil at a point higher than its regular boiling point. Changing the pressure conditions inside a sealed cooker means that the water is able to get much hotter without evaporating and when it finally turns into steam, the moisture-laden air is hotter than the steam that would come out of your tea kettle.

The trapped steam begins to work its magic immediately, since water is a good conductor of heat and all food stuff contains water. However, this is only half of the reason why it takes so little time to cook food inside a pressure cooker.

The increased pressure inside the cooker literally forces heat into the food. Think of the pressure as an invisible hand pushing the extra-hot steam into the very core of the food inside. However, if the pressure is like a crushing hand then why doesn’t the food come out all smashed? Well, this is because the steam applies uniform pressure to all surfaces of the food and that leaves the food un-smashed.


A pressure cooker is made up of a pot, a lid which fits precisely on the pot with a locking mechanism; a rubber ring that goes between the lid and the pot so that no air can escape; a valve on top of the lid with a release whistle.

There are 2 extremely important parts in all pressure cookers. The rubber ring that goes between the pot and the lid, ensures that no air escapes from inside the container; if it did, then the pressure would not be able to build up.

The valve on the top is a safety measure that makes sure the pressure does not build up to dangerous levels inside the pot. This could lead to a potentially dangerous explosion. It is designed to allow some of the steam to escape after the pressure inside reaches a certain point. And with that startling whistle, we know how much the food has been cooked.

Ask your mum how long different foods would take to cook inside a pressure cooker. Ask her to tell you in how many whistles, not actual time. When she is cooking these different foods see how long it actually takes.

Here are the names of different foods you can try:

  • 1 cup of rice
  • 4 potatoes
  • 1 cup of dal

For more such interesting Physics videos and articles visit our Physics for Kids category.