Viscosity and electrical conductivity of concentrated solutions of soluble coffee Original Research Article

Viscosity of concentrated aqueous solutions (ω=0.5–0.8) of soluble coffee was measured in the temperature range 25–95°C. After some time of the shear application in the viscometer and passing a temperature of 95°C, the rheological behaviour was found to be Newtonian. The viscosity was correlated by a five parameter function of coffee mass fraction and temperature. Specific electrical conductivity of coffee solutions in tap water (ω=0–0.8) was measured in the temperature range 25–72°C. A seven parameter model based on the assumption that the solution is composed of a partially dissociated species and water describes very well the measured data. A modified Casteel–Amis model equation has been identified for comparison. The conductivity dependence on mass fraction exhibits maxima, which are shifted towards higher concentrations the higher is the temperature. Viscosity, refractivity index, density and thermal conductivity of aqueous coffee solutions (ω=0–0.5) are reviewed.