Technical data sheet
This method is a measurement relating to the free, unbound water present in food and food products.
The atmosphere of a special sampling cell is evacuated, repressurized, and measured manometrically. The results are correlated to water activity in the sample.
Nearly all foods and food products
Samples containing high levels of propylene glycol
Water Activity Meter
Water activity (aw) is the ratio of the vapor pressure of the water in the sample to the vapor pressure of pure water at the same temperature.
Sample size requirements
Water activity has little, if any, relationship to the total moisture content of the food. Water activity does provide a means of assessing the storability and bacterial susceptibility of shelf-stable foods. It is known that microorganisms cannot survive below certain aw levels, depending on the type of microorganism with botuli at <0.93; bacteria at <0.86; yeast cells at <0.78, and mold spores at <0.65.