Do you know why it is easier to cook rice in a pressure cooker rather than in a open container?
Here is a simple answer-
Now,we all know that to make rice we need to boil it with water. When this happens,some of the water is soaked by the rice, and the rest becomes water vapour.But where does this vapour go?
It is trapped inside the pressure cooker along with the heat from the fire(because of the pressure). So,even after we put off the fire,the rice is still being cooked inside!
When you use a pressure cooker, a lot of gas is saved.
Thanks, Kamalini. Imagine the humble pressure cooker being a tool of science, But there's more to it. Why is the pressure important?
ReplyDeleteWell, interestingly enough, water doesn't always boil at 100ºC. A liquid boils when its 'vapour pressure' equals the atmospheric pressure. Now go up on Mount Everest. Because you are so high up, there's less atmosphere pressing down on you, so the air pressure is much lower. Now, since the vapour pressure has to reach a lower atmospheric pressure, the water will actually boil at a much lower temperature -- around 70ºC! Not good enough to cook your pulao.
What the pressure cooker does is to trap the steam. Now when you heat gas, the pressure increases. Pretty much like a class at school, the particles get excited but have nowhere to go, so they just push against the walls (and each other) harder. So the atmospheric pressure inside the cooker is increase. The water has to be heated more for its vapour pressure to get high enough. So the rice is cooked. At sea level or near-sea level (which is where we are) the boiling point increases to about 125ºC. That's why pressure cooking is faster.