An experimental set-up and a measurement technique were developed so that diffusion in model foods (gels of agar) could be visualised and quantified. The diffusion of aqueous solutions of varying concentrations of two dyes (rhodamine 6G and methylene blue) in gels of agar was followed in situ at three temperatures (30, 50, 70 degrees C) until equilibrium was reached. The nature of the diffusion process (in terms of the amount of dye diffused into the gel) was studied using image analysis techniques. The diffusion coefficient. D, was estimated using Fick's second law of diffusion and found to be similar to 10(-10) m(2) s(-1). The effect of the size of the diffusing molecule, as well as that of the processing temperature on diffusion was investigated and found to be significant. (C) 2012 Elsevier Ltd. All rights reserved.