Why do noodles shrink?

When noodles, pasta or dried beans are added to water and cooked, they absorb the water and the volume increases. As they cook, the internal pressure from the trapped water builds, creating a gelatinized texture.

When you drain the noodles or beans and then turn off the heat, the pressure inside them forces them to release some of the trapped water. As they release the water, the noodles or beans shrink back to a smaller size, sometimes up to half their original size.

The shrinking process continues as the noodles or beans cool down, as the steam and water vapor inside condense.