ABSTRACT
From a thermodynamic point of view, evaporation is simple, but the fact that most food is not stable thermodynamically but only metastable, with different time constants, makes it unrealistic to stick to the first-order equilibrium description. In this chapter, the authors consider some examples of evaporation, ranked by order of complexity. The dispersed system formalism can usefully indicate an order for discussing such a broad question as evaporation from food. Many phenomena occur simultaneously during such processes, including evaporation and steam extraction, such as in wine boiled for sauces, stocks for fond, glaces or demi glaces, for example. Concerning steam extraction, one is invited to look at the chapter on essential oils in this book, in which production processes of odorant compounds are discussed. Food science, and even more food technology, recognize so well the importance of water evaporation from such systems that a measurement of it was devised as "water activity".
