How can a steaming basket cook food above the water?

Dumplings or vegetables in a steaming basket can cook while sitting above the boiling water. Heat reaches them in moving water vapor, rather than by keeping the food under liquid water. Holes in the basket give the vapor a route around the food.

The heater supplies energy to the water below. Some water changes into vapor and rises into the covered space. When that vapor meets cooler food, some condenses into tiny drops. Condensing vapor releases energy to the food’s surface, helping warm it.

Heat then travels inward from the surface. A thick piece takes longer to warm through than a thin piece of the same material under similar conditions. Spaces between pieces let vapor reach more surfaces; a tightly packed pile can heat unevenly.

The lid helps keep the cooking space full of hot, moist air and vapor. An ordinary steamer is not sealed to build high pressure: vapor can escape. It therefore works differently from a pressure cooker, even though both use water and a lid.

The basket does two jobs at once. It supports the food above the liquid and leaves passages for heat-carrying vapor. A simple gap between water and food changes the cooking method. The visible white cloud outside the pot is mostly tiny liquid droplets; water vapor itself is invisible.