Drying

Drying preserves foods by reducing the tissue’s water content from around 90% to between 5 and 35%, a range in which very little can grow on it. This is one of the oldest preservative techniques; the sun, fire, and mounds of hot sand have been used to dry foods since prehistory. Fruits and vegetables usually benefit from treatments to inactivate the enzymes that cause vitamin and color damage. Commercially dried vegetables are usually blanched; and fruits are dipped or sprayed with a number of sulfur compounds that prevent oxidation and thereby enzymatic browning and the loss of antioxidant phenolic compounds, vitamins, and flavor. While sun-drying used to be the most common treatment for prunes, raisins, apricots, and figs, forced hot air-drying is now widely used because it is more predictable. Home and restaurant cooks can use the oven or small electric driers whose temperature is easier to control. Fruits and vegetables are dried at relatively low temperatures, 130–160°F/55–70°C, to minimize the loss of flavor and color and prevent the surface from drying too fast and impeding moisture loss from within. Pureed fruits are spread out into thin sheets to make “fruit leather.” Relatively moist dried fruits and vegetables are nicely soft, but they’re also vulnerable to some hardy yeasts and molds, and therefore are best stored in the refrigerator.