Freeze-Drying

Freeze-drying is a controlled version of freezer burn: it removes moisture not by evaporation but by sublimation, the transformation of ice directly into water vapor. Although we think of freeze-drying as a recent industrial innovation, the natives of Peru have been freeze-drying potatoes in the Andes for millennia. To make chuño, which can be stored indefinitely, they trample potatoes to break down their structure and expose them constantly to the dry, cold mountain air, so that they freeze at night and lose some moisture by sublimation, then thaw during the day and lose more water by evaporation. Chuño develops a strong flavor from the disruption of the potato tissues and long exposure to the air and sun, and is reconstituted in water to make stews.