Drying 2004 – Proceedings of the 14th International Drying Symposium (IDS 2004) São Paulo, Brazil, 22-25 August 2004, vol. C, pp. 1604-1611 1604 SHRINKAGE, DENSITY AND POROSITY VARIATIONS DURING THE CONVECTIVE DRYING OF POTATO STARCH GEL A.H. Al-Muhtaseb, W.A.M McMinn. and T.R.A. Magee Food Process Engineering Research Group, School of Chemical Engineering, Queen’s University Belfast, BT9 5AG, UK, e-mail: w.mcminn@qub.ac.uk Keywords: convective drying, density, porosity, potato starch gel, shrinkage ABSTRACT Quality factors are those that determine the worth, or value, of a food product to the consumer. A thorough understanding of the factors affecting the quality of the product is thus of major relevance. With this in mind, the macro-structural properties (porosity, bulk and particle density) and physical changes (shrinkage) of cylindrical potato starch gel samples during convective drying were examined. Moisture removal was accompanied by the formation of a dense structure, with air temperature imparting a negligible influence. The system also exhibited a non-linear increase in particle density with decreasing moisture content. Drying, however, induced limited internal porosity development, i.e. ε < 10%. Volumetric shrinkage of the potato starch gel samples decreased almost linearly with moisture content. INTRODUCTION Drying of food is a heat and mass transfer operation in a multiphase system and takes place simultaneously with physical and microstructural modifications (Nieto et al., 2003), which affect the quality of the dehydrated product. Quality factors are those that determine the worth, or value, of a food product to the consumer (Aguilera & Stanley, 1999). This broad definition encompasses many different factors, including colour, texture, shape, size, porosity, density and shrinkage (Krokida & Maroulis, 2001). Therefore, examination of the physical properties of foods, and their responses to process conditions, is crucial for analysis of the drying process (Tsen & King, 2002). Bulk and particle densities are vital parameters in the design, modelling and optimisation of food processing operations because they have a direct affect on the thermo-physical properties of food materials (Rahman, 1995). Density characteristics are influenced by the method and rate of drying, where slow drying yields a fully consolidated product and accelerated drying results in a solid comprised of cracks and holes with a lower density (Brennan, 1990).