Water activity provides the basis of shelf stability and is considered a critical control point for preventing microbial contamination in edible products or chemical reactions in biomass. The resulting measurement ranges from 0.00 Aw/g (completely dry sample) to 1.00 Aw/g (pure water).
Water activity (Aw) is a measure of energy, it’s a ratio between the vapor pressure of the sample and the surrounding enclosed air. Water activity is measured with an water activity meter that has a chilled-mirror dew point sensor. Unlike other water activity sensors, the dew point sensor measures water activity directly. Samples are enclosed in a sealed container, then the relative humidity in the headspace will equalize with the water activity of the sample, the relative humidity of the air in the headspace in measured to determine the water activity.