An underground pressure cooker
The traditional curanto of Chiloé is a display of thermal engineering that predates modern cookware by millennia. The process begins by digging a pit, typically about a half-meter deep, and lining it with smooth, non-porous river stones. A fire is built on top of these stones and burns for several hours until they are glowing red-hot. Once the stones reach the required temperature, the embers are swept away, and the cooking process begins with remarkable speed to conserve the stored thermal energy.
The first layer placed directly on the hot stones often consists of shellfish, such as mussels (choros) and clams (almejas). The heat from the stones instantly vaporizes the liquid from the shellfish, creating a massive amount of steam. Subsequent layers of pork, chicken, sausages, potatoes, and potato-based breads called milcao and chapalele are added on top. Each layer of food is separated by massive leaves from the nalca plant (Gunnera tinctoria), a species called Chilean rhubarb. These waterproof leaves can grow up to 2.5 meters in diameter and act as a gasket, trapping the steam inside the pit. Finally, the entire pit is covered with wet sacks and a thick layer of turf and soil, creating a sealed, subterranean pressure cooker.