Water activity (aw value) is the most important factor in assessing the likely growth of micro-organisms in foodstuffs and the rate at which this growth will occur. Consequently the aw-value gives important information as to the durability of food and food products. Other factors are temperature and the pH factor of the product. For example, a madeira cake with a water activity value (aw-value) of 0.81 (or ERH of 81%) has an expected minimum shelf-life free of mould of 14 days at a temperature of 27°C or 24 days at 21°C. On the other hand, with an increased water activity value of 0.85 and a temperature of 27°C the shelf-life would be 8 days or 12 days at 21°C. Should the aw value need to be determined inline, our DWF-RF-25 device is suitable for this task.