Thermal treatment of many foodstuffs is a common operation in the food industry in order to increase the storage life of the marketed product. The control and the knowledge of heterogeneity of treatment which may occur during cooking of texturant products in process equipment are essential to ensure food quality. In this paper, a non-intrusive ring sensor device has been set-up at the inner wall of a vessel as made in tomographic processes. Based on electrical properties measurement and a novel approach in the way the sensor is applied, the presence of structural heterogeneities was detected. This device has been also used to estimate in real time thermal heterogeneities during cooking of a starch-based product in an agitated vessel. The paper describes in details the measuring system, the reconstruction algorithm for the temperature fields and the structure change detection algorithm. Pictures visualizing the temperature fields during cooking of a model fluid are reported in the last section. (c) 2006 Elsevier B.V. All rights reserved.