The freshly lifted potatoes are washed clean without damaging the skins and laid out on soft turf or straw padding to be exposed to severe night frost. As soon as they have thawed in the morning they are trodden with bare feet so that the skin remains intact but the fluid resulting from cell rupture is extruded. On the first pressing over 30 per cent of the fluid may be lost. They are left in position and dried by the sun and wind. The process is repeated for five successive days. From the sixth day onwards no further pressing takes place and they are straw-covered to a sufficient depth to prevent further freezing at night. Once dried they are as hard as stone and can be stored indefinitely, and even a minor degree of damp does not seem to damage them unduly. This product is called chuño.