Although the pressure cooker has come into use only in modern times it was invented before the steam-engine. Its inventor, the French physicist Denis Papin, regarded it as no more than a stepping stone to the steam-engine that he was hoping to build. He called it a 'bone digester' and demonstrated its efficiency by cooking a meal for a distinguished group of scientists at the Royal Society in London in 1679. His cooker even had a safety valve, which in itself was an important invention, being the first of its kind.
In the modern pressure cooker food is put in together with a very small amount of water. The tightly fitting lid is clamped on and the cooker is heated on a stove to a temperature exceeding 99 °C. As the steam cannot escape pressure builds up and this causes the food to cook much faster and more thoroughly than in an ordinary saucepan. Pressure cookers retain the maximum nutritive value of the food and are very economical in terms of time, heat energy and also food costs, because cheaper, tougher cuts of meat can be utilized. Vegetables, too, maintain their texture and flavor when cooked in this manner. Pressure cookers can be obtained in sizes ranging from 2 to 20 liters. The larger ones have racks and internal pans so that a variety of food may be cooked at one time.