Effects of order of mixing and solute interactions on the "water activity" of concentrated solutions

Experimental results indicate that order-of-mixing effects in concentrated sugar-salt solutions are functions of salt:sugar concentrations, types of sugars and salts, time after mixing of clear solutions, and solute interactions. Visual clarity of the solutions after preparation and at least 16 hours of storage may not be a sufficient indicator of complete solvation. The order of mixing solutes may cause differences in their rates of hydration, resulting in differences in "Aw" at non-equilibrium conditions, whereas Aw is only meaningful at thermodynamic equilibrium. Determining a thermodynamic equilibrium Aw in diffusion-resistant foods may take much more time and be more difficult to measure than in the solutions reported in this paper.