The moment a pressure cooker is placed over a flame, the water inside begins to heat up. As the temperature reaches its boiling point, liquid water transforms into steam. In an ordinary saucepan, that steam simply drifts into the air. A pressure cooker, however, locks it inside.
With nowhere to escape, steam begins filling every corner of the sealed vessel. Molecules move faster, collide more frequently and gradually increase the pressure inside the cooker. That trapped steam is what makes a pressure cooker far more efficient than conventional cooking. According to researchers at North Carolina State University, once steam is confined inside the sealed pot, both pressure and temperature rise together, allowing food to cook much faster than it would in an open pan.
