What is freeze drying (FD) in freeze dried fruit processing?

Freeze drying (FD) is a low temperature dehydration process that involves freezing the product and lowering pressure, removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using hot air drying. Freeze drying preserves the shape, color, flavor, and nutritional value of the product, making it a suitable method for freeze dried fruit, foods, pharmaceuticals, and biological materials.