Density, viscosity and coefficient of thermal expansion of clear grape juice at different soluble solid concentrations and temperatures C.A. Zuritz a, * , E. Mun ˜oz Puntes b , H.H. Mathey a,z , E.H. Pe ´rez a , A. Gasco ´n a , L.A. Rubio b , C.A. Carullo b , R.E. Chernikoff b , M.S. Cabeza b a Facultad de Ciencias Agrarias, UNCuyo, Alte. Brown 500, (5505) Chacras de Coria, Mendoza, Argentina b Facultad de Ciencias Aplicadas a la Industria, UNCuyo, Av. San Martı ´n 358, San Rafael, Mendoza 5600, Argentina Received 12 July 2004; accepted 24 October 2004 Available online 10 December 2004 Abstract 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 (r 2 > 0.992). The values of activation energy (E a ) 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. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Density; Coefficient of thermal expansion; Viscosity; Rheology; Grape juice 1. Introduction Concentrated clear grape juices are extensively used in the enological industry. Their use as constituents of juices, jellies, marmalades, jams, colas, beverages, etc., generates a consumer market with an increasing demand because they are natural products with an industrial ver- satility that allows them to compete with other fruit juices. Argentina is one of the principal producers and exporters of concentrated clear grape juices in the world. They are produced mainly in the provinces of Mendoza and San Juan (Argentine Republic) from the virgin grape juice and in the most part from sulfited grape juices. The province of MendozaÕs legislation establishes that a portion of the grapes must be used for making concentrated clear grape juices. This product has reached a high level of penetration in the export market and constitutes an important and growing productive alternative. An adequate manufacturing process, a correct design of the concentrate plants and an appropriate evaluation of their performance will facilitate optimization of the concentrated juices quality parameters. The plant effi- ciency is obtained from knowledge of the physics properties of the raw material and products. These 0260-8774/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.10.026 * Corresponding author. Tel.: +54 2627 430673; fax: +54 2627 421947. E-mail address: emunoz@fcai.uncu.edu.ar (E.M. Puntes). z Deceased. www.elsevier.com/locate/jfoodeng Journal of Food Engineering 71 (2005) 143–149