Real-time monitoring of chocolate extrusion by signal processing of pressure transducer data

The local fluctuations in pressure observed at the die during the extrusion of paste-like material have been shown previously to contain useful information about the processing behaviour and microstructure of the material. Previous investigations in this area have featured data processing post-operatively, and this paper reports the development of techniques to track material inhomogeneity, bursting of bubbles and breakdown of agglomerates on-line. The methods are applied to the continuous extrusion of solid chocolate ('cold extrusion') on an industrial pilot plant screw extruder and feature certain shortcuts in order to achieve signal de-noising. The results obtained are consistent with previous post-operative studies and indicate that the approach can be applied to monitor the performance of these processes on-line. (c) 2005 Elsevier Ltd. All rights reserved.