The high sugar and acid content of fruits make them safe to dry out-of-doors when conditions are favorable for drying. Vegetables (with the exception of vine dried beans) and meats are not recommended for out-of-doors drying. Vegetables are low in sugar and acid. This increases the risks for food spoilage. Meats are high in protein, making them ideal for microbial growth when heat and humidity cannot be controlled. It is best to dry meats and vegetables indoors using controlled conditions of an oven or food dehydrator.
Sun-dried raisins are the best known of all dried foods. California produces much of the world's supply of raisins. In the San Joaquin Valley, warm temperatures, low humidity and a constant breeze are ideal conditions for drying grapes.
To dry fruits out-of-doors hot, dry, breezy days are best. A minimum temperature of 85ºF is needed with higher temperatures being better. It takes several days to dry foods out-of-doors. Because the weather is uncontrollable, drying fruits out-of-doors can be risky. If it rains in California while the grapes are drying, the entire supply of raisins can be destroyed.
High humidity in the South is a problem for drying fruits out-of-doors. A humidity below 60 percent is best. Often these ideal conditions are not available when the fruit ripens and other alternatives to dry the food are needed.
Fruits dried out-of-doors must be covered or brought under shelter at night. The cool night air condenses and could add moisture back to the food, thus slowing down the drying process.
Racks or screens placed on blocks allow for better air movement around the food. Because the ground may be moist, it is best to place the racks or screens on a concrete driveway or if possible over a sheet of aluminum or tin. The reflection of the sun on the metal increases the drying temperature.
Screens need to be safe for contact with food. The best screens are stainless steel, Teflon-coated fiberglass and plastic. Avoid screens made from "hardware cloth." This is galvanized metal cloth that is coated with cadmium or zinc. These metals can oxidize, leaving harmful residues on the food. Also avoid copper and aluminum screening. Copper destroys vitamin C and increases oxidation. Aluminum tends to discolor and corrode.
Because birds and insects are attracted to dried fruits, two screens are best for drying food. One screen acts as a shelf and the other as a protective cover. Cheesecloth could also be used to cover the food.
Info found at : http://www.uga.edu/nchfp/how/dry/sun.html