Freezing Technology

3.6.1. Introduction

Heat is used to dry foods or concentrates liquids by boiling to remove water and therefore preserves the food by reduction in water activity. However, heat causes a loss of sensory and nutritional qualities. In freeze drying a similar preservative effect is achieved by reduction in water activity without heating the food and sensory and nutritional qualities are consequently better retained. However both, operations (freezing & drying) are slower than conventional dehydration. Freeze drying has become an important commercial operation to dry expensive foods which have delicate aroma or texture (for example instant coffee, mushrooms, fruit juices and sea foods).