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  • Category: Science

    How a pressure cooker cooks so fast?


    Want to know how pressure cookers can cook fast? Find out why less time is required to cook and boil and pressure cooks than in normal utensils.

    Dear experts,
    When we boil potatoes in a saucepan, they take 20-30 minutes to cook. But boil them in a pressure cooker, and the will be ready in 4-5 minutes. why?
    Even though the saucepan and pressure cooker made with same material and the heat used same for both methods. How the cooker helps to boil early than saucepan.
  • Answers

    9 Answers found.
  • We know that water boils at 100 degree Celsius. In an open container, even on adding more heat to the water, it's temperature remains constant. This is because of evaporation. Wen heat is added, the excess heat is used for the evaporation of water and the overall temperature remains the same.


    The pressure cooker cooks faster because it is a closed container, plain and simple.

    When we heat water in a closed container as we add more heat, by increasing the temperature, the steam will be trapped because it is a sealed environment, resulting in the build up of pressure.

    The temperature and pressure are directly proportional to each other.
    Water vapor trapped inside the closed container under pressure allows the temperature to rise beyond what it could reach normally in a traditional uncovered vessel.
    The build up of pressure and heat are the factors which enable pressure cookers to cook foods faster and more efficiently.

    This is why the cooker cooks faster than the saucepan.

  • Sir,

    The basic principle of pressure cooker is very simple. The principle is

    "Boiling point of a liquid is inversely proportional to the pressure around it"

    In pressure cooker, when water inside it was heated, steam is generated and there is no outlet to go. So, steam will accumulate inside and pressure builds up. Due to that pressure, the boiling point of water decreases, so cooking is done at low temperatures. Thus Potatoes are cooked quickly and in a effective manner. But in sauce pan, there is no such mechanism. Thus, Pressure cooker saves the time and fuel. These are very useful in cold areas where more heat is required to boil the water.

    Regards,
    Mandeep.
    Editor.
    "Hard work never goes unvalued"

  • In pressure cooker the water gets boiled and steam created remains inside the cooker creating a high pressure helps the content to get boiled quickly as steam do not escape due to the presence of rubber tube around the cooker's lid.

  • The answer to the question why food cook faster in a pressure cooker is directly related with it's basic principle of the working, which can be stated as follows:
    When ever there is an increase in pressure in a closed system, it leads to an increase in temperature. This increased temperature leads to the quick cooking of the food inside a pressure cooker.

    In a pressure cooker, we cook in a sealed vessel which does not permit steam or liquids to escape unlike in an open vessel.
    Boiling takes place when the atmospheric pressure just above the surface of the food is equal to the pressure on the surface of the food, so that easy exchange of energy at constant temperature takes place. In an open vessel, to equate these two pressures, a lot of heat energy is required; whereas in a pressure cooker, it is very easy to reach a state of equilibrium with the two above mentioned pressures becoming equal soon due to close nature of the system and thus boiling starts very early.

    Increased pressure inside the pressure cooker, increases the boiling point of water in it and thus quick cooking takes place. At higher altitudes, where atmospheric pressure is low, the boiling temperature of liquids also gets lowers as pressure is directly proportional to temperature.

    ________
    Regards,
    JS.

  • Boiling point of water rises with increasing of atmospheric pressure. At 1 atm pressure the boiling point of pure water is 100 degree centegrade. But pressure cooker is a close system and water boils in it at almost 120 degree centegrade due to high pressure. But a saupan is an open system and water boils at 100 degree C in it. So potatoes get boiled in pressure cooker very easily.

  • Understanding the working of pressure cookers is very interest of subject. The physical principle is used here. Generally water boils at 100°C and it will not rise above that temperature under normal
    conditions. when water boils, steam is generated and stays at 100°C in an open environment. But if water is boiled in a closed environment, there is a buildup of pressure, which tends to force an increase in the temperature resulting in saving time for cooking. Even though that same materials are used in both saucepan and pressure cooler, conductvity of saucepan b may be
    That is all.

    Jeba.

  • Thank you dear members,
    The members responded all with nearly the same answers. But JyotiS has given detailed answer.
    Here the principle is a direct proportion between temperature and pressure created in the cooker. The temperature increasing simultaneously the pressure increases. The heat from temperature and the heat from pressure combined the double heat helps to cook so fast.

    "Education is the movement from darkness to light"

    Regards,
    3Nadh.

  • Hello Mandeep, you tried to given answer to this question but you wrongly mentioned, "Boiling point of a liquid is inversely proportional to the pressure around it" But as per Physics law, boiling point is directly proportional to the pressure. Hence I would like to request you to edit you response otherwise visitor will be misguided.

    Dr. Paresh B. Gujarati.
    Mechanical Engineer.
    'I'mprovement always begins with 'I'.

  • When water in the cooker reaches boiling point then water become steam. Specific volume of steam is more and it will expand. If these is no way for steam to go out then the pressure inside the cooker increase. When pressure increase then latent heat require for phase change (from water to steam) is less. So easily water became steam with less latent heat energy. It helps cooking food with less time and energy. All the thermal power plants also working in the same principle. Boilers are working as pressure cooker to generate the steam at high pressure. So the latent heat for vaporization is less. With less latent heat energy steam is generated for generating the electricity.

    Regards
    N. Srinivasan


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