Why can a pressure cooker cook above water’s usual boiling temperature?

Water does not have one boiling temperature under every condition. It boils when vapor bubbles can persist within the liquid against the surrounding pressure. At ordinary sea-level atmospheric pressure, pure water boils near 100°C. Greater pressure makes bubble formation possible only at a higher temperature.

A pressure cooker uses this relationship. Heat enters through the pot, and some water becomes vapor. Once the cooker is sealed for its pressure-cooking stage, vapor can build pressure above the liquid. The pressure-resistant body and secured lid contain that pressure. Water can then remain liquid, and cook food, at temperatures above 100°C.

The diagram compares two supplied absolute pressures. Near 101 kilopascals, water’s boiling temperature is about 100°C; near 200 kilopascals it is about 120°C. Absolute pressure counts pressure from zero, unlike a gauge reading that counts only the excess above the surrounding air. These are rounded physical examples, not settings for a particular appliance.

Higher temperature can speed many changes involved in cooking. Pressure alone does not replace the need to supply heat. A regulator limits normal operating pressure by controlling heating or steam release, depending on the design. Separate safety mechanisms address abnormal pressure, and a lid interlock prevents ordinary opening while pressurized. The drawing explains these functions rather than giving operating directions.