Introduction to Low Pressure Processes

Abstract

This chapter deals with general aspects of food vacuum drying. Food drying under vacuum presents several advantages over conventional atmospheric drying. Vacuum drying takes place in the absence of oxygen and at mild temperature, thus preserving most of the food nutritive and sensory characteristics. Nevertheless, it is usually a more costly process when compared to atmospheric drying. Conventional vacuum drying, freeze-drying, microwave-vacuum drying and related processes are the most known vacuum drying processes. While conventional vacuum drying is the cheapest process, microwave-vacuum drying is the fastest and freeze-drying provides the product with the best quality. On the other hand, conventional vacuum drying yields products of inferior quality and freeze-drying is very expensive, while microwave-vacuum drying presents intermediate costs and provides the product with acceptable quality. Summarizing, each one of these processes presents strengths and weaknesses in terms of engineering and quality aspects. The choice for one or other vacuum drying technique will depend on the needs to be fulfilled.