ABSTRACT
Water is an important component of all biological systems: in fresh foods, the percentage of water can vary from 60% to more than 90%. During processing, storage, and distribution of foodstuffs, water can be responsible for changes in the physical, chemical, and/or biological characteristics: moisture content has thus to be reduced in order to avoid deterioration of aroma compounds or degradation of nutritional substances. Air drying is one of the oldest methods used to preserve foods: the product is exposed to a continuously ›owing stream of hot air causing the evaporation of the moisture. The dehydrated products can have an extended life of a year, but the quality can be drastically lowered. Other processes can be used in order to improve the quality of the dried product, for example, vacuum freeze drying (FD). In FD, water is removed from a frozen product by sublimation: the driving force is given by the vapor pressure difference between the ice front and the surrounding environment.
