MATHEMATICAL MODELING OF TRANSIENT HEAT zy AND MASS TRANSPORT IN A BAKING BISCUIT MUSTAFA OZILGEN zyxw Food Engineering Department Middle East Technical University zyx 06531 Ankara, Turkey zyx and J.R. HEIL Department of Food Science and Technology University of California Davis, CA 95616 Accepted for Publication November zyxw 15, 1993 ABSTRACT Drying behavior of a single baking biscuit was modeled using unsteady state, anisotropic, two dimensional, simultaneous heat and mass balances. Solutions of these equations agreed well with the experimentally determined temperature and the moisture data. Modeling revealed that in the outer sections of the baking biscuit conduction and diffusion were the dominant heat and mass transfer mechanisms, respectively. In the central section of the biscuit the gas cells cracked with the increased vapor pressure and the upward volume expansion, then airhapor enclaves were formed among the horizontal dough layers in the radial direction. The dominant heat and mass transfer mechanisms in the central section of the biscuit were convection. Presence of two different regime zones in a baking biscuit may have important consequences concerning the strength of the commercial products against crumbling during marketing and consumption. INTRODUCTION Heat effects create a number of physical and chemical changes in a biscuit during baking including gas formation, denaturation and coagulation of proteins, gelatinization of starch, crust formation, browning reactions, evaporation zy of water, expansion of volume, and development of porous structure (Smith 1966). Although the dough may be homogeneous at the beginning of a baking process, Journal of Food Processing and Preservation 18 (1994) 133-148. All Rights Reserved. Copyright 1994 by Food zyxwvuts & Nutrition Press, Inc., Trumbull, Connecticut 133