A mathematical model able to predict the starch retrogradation kinetic of durum wheat bread and its influence on the crumb firming process is presented. The proposed model consists of two equations: the first is used to predict the evolution during storage of starch crystallinity level, and the second is used to relate the starch crystallinity level to the crumb elastic modulus. To validate the proposed model accelerated tests were conducted conditioning the samples at 5 degreesC and at two different water activities: 1.0 and 0.877. To monitor both the starch retrogradation kinetic and the crumb firming process during storage, wide-angle X-ray diffraction and compression tests were used respectively. The experimental results were successfully fitted by means of the proposed model. The analysis of the data evidenced that by reducing the water activity from 1.0 to 0.877 the overall starch crystal growth rate increase due to the increase of starch nucleation rate. (C) 2003 Elsevier Science Ltd. All rights reserved.