Density, viscosity and coefficient of thermal expansion of clear grape juice at different soluble solid concentrations and temperatures

The effect of temperature and soluble solids concentration on density, coefficient of thermal expansion and viscosity of clear grape juices from Mendoza, Argentina, collected during 1999 and 2001, was studied. The juice was obtained from different sections of a commercial evaporator at concentrations ranging from 22.9-70.6 °Brix. The properties were measured between 20 °C and 80 °C, in 10 °C increments. It was also characterized in terms of extract, reducing sugars and refractive index at 20 °C. The density was correlated as a function of absolute temperature and degrees Brix. The coefficient of thermal expansion was computed from its thermodynamic definition at constant pressure. The juices showed a Newtonian flow behavior within the range of variables studied. The effect of temperature was very well correlated with the Arrhenius equation (r2 > 0.992). The values of activation energy (Ea) increased with solid concentration from 16.3 to 52.0 kJ/mol. An equation to predict the viscosity in terms of temperature and soluble solids concentration was derived. Published predictive equations are statistically different from the equations derived here.