Pressure cooking is sometimes applied to vegetables, especially in the canning of low-acid foods. It is essentially cooking by a combination of boiling water and steam, except that both are at about 250°F/120°C rather than 212°F/100°C. (Enclosing the water in an airtight container traps the water vapor, which in turn raises the boiling point of the water.) Pressure cooking heats foods very rapidly, which means that it’s also very easy to overcook fresh vegetables. It’s best to follow specialized recipes closely.