Why use a pressure cooker to cook food easily?
Pressure cookers, when boilers are heated, the pressure in the pot is very high. Why in high pressure conditions is the food in the pot easy to cook?
Under standard atmospheric pressure, the boiling point of water is 100 ° C. Using a conventional pot to cook food, the temperature in the pot cannot be higher than 100 ° C. When the fire is raised or the cooking time is prolonged, the result can only cause the water from the liquid to turn into gas, which means evaporation. The temperature of water cannot exceed 100 ° C. That’s because water molecules at 100 ° C already have enough energy to dislodge the barrier of air molecules that become water vapor. But if the pressure of the surrounding air is high, then the water molecule must have a higher energy to overcome the airborne “barrier” to enter the air, turning into water vapor. . The energy of a water molecule completely depends on the temperature of the water itself. The higher the temperature, the greater the energy of the water molecule. Therefore, if you want to boil water in a higher boiling point temperature, cook food faster then you must increase the pressure in the pot.
On the ground, the object is subjected to an atmospheric pressure of about 101.3 kPa. From the ground going deep into the ground, the depth kept increasing by 1,000 m, following the increasing pressure pressure, the boiling point of the water rose 3 ° C. In a mine at a depth of 300 m, water must reach 101 ° C to boil. If you want to bring water to 200 ° C to boil, the pressure in the pot must reach 1418.2 kPa (14.18 at).
Taking advantage of the above principle, people made a pressure cooker. Its biggest feature is its good sealing performance. When the water reaches 100 ° C and begins to boil, the water molecule does not escape from the pot, causing the pressure in the pot to increase gradually. The rise of barometric pressure leads to an increase in the boiling point. So the cookware in the pot can continue to absorb the heat. So the food is easy to cook. The temperature in a pressure cooker can generally reach 120 ° C or higher. At such a temperature, the starch easily becomes a paste, so that the rice is easily cooked into cooked rice. To prevent the pressure in the pressure cooker from being too big, leading to the explosion, the safety valve is fitted on the lid. When the pressure in the pot exceeds the specified value, a part of the high pressure steam penetrates the safety valve to escape, thereby making the pot maintain a certain pressure.
Under low pressure situation, the boiling point of water will also drop. For example, when boiling water on Mount Everest, the water reaches 73.5 ° C, it begins to boil. At such temperatures, the food is difficult to cook. So in the low pressure region on the plateau, taking advantage of a pressure cooker to cook food is the most effective way of cooking.
Photo by Dimitris Graffin