Pretreatment is not necessary for successful drying, but it can enhance the color, flavor, and texture of certain foods.
Pretreatment options include dipping, blanching, marinating, and sulfuring.
Pretreatment affects the enzymes, a group of special proteins that cause chemical reactions-ripening and eventual spoilage-and determine the color, texture, flavor, and aroma of certain foods. The microorganisms that cause spoilage need moisture to live and reproduce. Drying foods above 140°F halts enzyme activity.
Foods also contain simple yeasts, molds, and bacteria, all of which can cause deterioration. Again, reducing the moisture content of food inhibits their growth. When dried, vegetables contain only about 3 percent moisture, and fruits, depending upon sugar content, up to 15 percent water.
For an in-depth discussion of pretreatment methods for fruits and vegetables, see pages 33-37.