Brownian motion and Einstein relation for migration of coffee particles in coffee suspensions

BACKGROUND: The migration of particles in a liquid plays an important role in determining the stability of the corresponding suspension. The preparation of a cup of coffee involves the migration/dispersion of coffee particles in aqueous solutions. We investigate the Brownian motion of coffee particles in coffee suspensions at different temperatures for three different coffee beans via the migration of the coffee particles of the coffee suspensions in water. RESULTS: The activation energies for the Brownian motion of the coffee particles are in the range 23.5–32.0 kJ mol⁻¹, relatively independent of the size of the coffee particles used in the present study. The viscosities of the coffee suspensions are measured as a function of temperature and then used to correlate with the gradient–diffusion coefficient for the Brownian motion of the coffee particles. The activation energies of the rate process controlling the viscous flow of the coffee suspensions are in the range 12.7–14.1 kJ mol⁻¹. CONCLUSION: The correlation between the viscosity and gradient–diffusion coefficient of the coffee suspensions generally follows the Einstein relation. A temperature dependence exists for the viscosity and gradient–diffusion coefficient of the coffee suspensions, which can be used to understand the brewing of coffee at high temperatures with respect to product refinement.