The evaluation of water activity in aqueous solutions from freezing point depression

The water activity of various non-electrolyte and electrolyte solutions of interest for aW inhibition of microorganisms, has been calculated from freezing point data and compared with aW values measured at 25°C. It is shown that in the important range of aW, 0.96–0.85, the error introduced by assuming that the aW at the freezing point is the same as that at ‘room’ temperature, is relatively small. In the majority of cases the difference is not likely to be larger than about 0.01 aW units.