The water activity (aw-value), plays a crucial role in the food industry throughout processing and in determining durability. Water activity is defined as the humidity value by which a balance between the unbound water (not chemically or physically bounded water) and the humidity in the ambient surrounding is achieved. This process is caused by partial water vapour pressure. In the laboratory the water activity can be determined, for example, using a capacitive polymer sensor set in an enclosed container containing the material to be measured. The measurement is taken in or immediately above the material sample and as little air as possible should be present to ensure a speedy and reliable measurement. During the production process a cover of suitable dimensions must be put in place at appropriate stages of production in order to determine the water activity in the described manner.

The equilibrium moisture od water activity gives a very good indication concerning the durability of foodstuff Determination of Water Activity
The book deals with all aspects of humidity and moisture measurement Moisture Measurement
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