• drying;
  • diffusion;
  • modeling;
  • hygroscopic;
  • porous

ABSTRACT: The experimental method of measuring the effective moisture diffusivity of bread, the representative hygroscopic porous material, was investigated. Drying curves and temperature profiles were obtained from cylindrical bread samples (0.3 and 0.6 porosity, and 0.011 and 0.018 m dia) under convective hot air conditions (50 to 90 °C oven temperatures and 1 to 3 m/s air velocity). The normalized drying curves were linear, suggesting that Fick's diffusion equation was applicable in determining the diffusion coefficient, and the effective moisture diffusivities were in the range of reported values. Experimental determination of the temperature dependent diffusion coefficient requires isothermal conditions to exist in the material, but temperature gradients existed throughout drying of the bread samples. Thus, the linearity of normalized drying curves is not a guarantee that the moisture diffusivity is properly determined. The need to develop an apparatus to achieve isothermal conditions during experimental measurement of the effective moisture diffusivity is shown.