Kusun (headspace depth in a tank)

Kusun (空寸) refers to the depth from the top of a container, such as a tank holding moromi (fermentation mash) or sake, down to the actual surface of the liquid inside, measured from the full level. Specifically, it is the distance from the rim of the vessel to the liquid surface. Measuring it makes it possible to gauge and manage the volume of liquid during fermentation and storage, so it serves as an important indicator. In the sake brewing process, this measurement is used to check that fermentation is progressing properly and to confirm how much liquid remains in the container.