Water, essential element to all forms of life, is found in varying amounts in the foods we consume ; and while it does not provide energy value, it influences the foods’ properties particularly their proneness to degradation. Water also has an impact on the appearance, texture and flavor of the food.

Water activity is one of the main parameters as regards a product’s shelf life, be it food, pharmaceuticals, cosmetics, or agricultural seeds. Measuring such activity makes it possible to control and optimize the manufacturing and preservation process to ensure mechanical, physical, chemical and microbiological stability. The measurement of water activity is decisive for the quality and health safety of a product, especially if it is not sterilized or stored in a non-sterile environment. Aw measures form part of the calculation of the CSD and MDD of many products.

Although the concept of water activity emerged and started developing in the 70’s and 80’s, the primary means for correcting water activity have been known since Antiquity, and probably before then: drying, or adding an Aw reducing agent such as sodium chloride (salt) for sausages, or sucrose (sugar or formerly honey) for jams.