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.
Freeze drying consists of three stages: freezing, sublimation drying, and desorption drying. Freezing is the most critical stage as it determines the size and shape of the ice crystals and affects the final product quality. Sublimation drying removes about 95% of the water present in the product by applying heat and vacuum. Desorption drying removes the remaining unfrozen water molecules by raising the temperature higher than in sublimation drying.In freeze dried fruit processing, fruits with high water content such as strawberries, mango, pineapple, banana, dragon fruit (pitaya), jackfruit, and durian are among the most popular choices for freeze-drying. Freeze-drying preserves their shape, color, flavor, and nutritional value making it a suitable method for fruits.