Pressure Cooker Physics

A pressure cooker traps steam, raising the internal pressure above normal atmospheric levels. Higher pressure raises the boiling point of water — from 100 degrees Celsius at sea level to about 121 degrees inside a typical pressure cooker.

That extra 21 degrees dramatically speeds up cooking. Tough collagen in meat breaks down in 45 minutes instead of three hours. Dried beans soften in a fraction of the usual time. The sealed environment also prevents flavor compounds from escaping as steam.