Water activity is a measure that reflects the "free water concentration" in a final product. This is not equal to the amount of water incorporated, but a value that describes the availability of this water. It can be crucial for the biological stability of technical products as well as food. Thus, e.g. Sugar and related substances Water, which leads to a decrease in water activity - and consequently leads to an increase in microbiological stability. The preparation of preservative-free products can therefore be e.g. by formulation of larger amounts of sugars, such as sorbitol or xylitol done.
By measuring the water vapor partial pressure, it is possible for us with a special apparatus to measure the water activity of a product and to obtain an indication of possible biological stability.