Solutes and low water activity

It has been known from ancient times that the drying of fresh foods prolongs their edible life. Different foods respond more or less well to drying, retaining not only quantitatively different amounts of residual water but undergoing qualitatively different ultrastructural changes; this influences their organoleptic qualities, as does the need or not to rehydrate the food prior to consumption. The amount of water in the food does not give a good correlation with the stability of the food in relation to microbial spoilage when various products are compared. It was not until it was realized that what is important is the state of water in food, or more precisely the “availability” of water in foods, that sensible correlations could be made.