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Title: Agglomerate breakdown in relation to the mixing of chocolate
Author: Kontogiannis, Dimitrios
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2008
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The main objective of this study was to develop the understanding of the optimum mixing conditions in chocolate. An important aspect of chocolate production is the assessment of the agglomerates in the mixture, formed by the ingredients of chocolate during the grinding stage and broken down to an extent, during conching. In order to assess agglomerate breakdown during mixing, a simplified chocolate was subjected to a variety of procedures. Mixing experiments took place in an apparatus known as the Reciprocating Multihole Extruder (RME). The RME consists of a cylindrical chamber, within which a die plate can oscillate and rotate through the material. Industrial chocolate was subjected to extrusion at different temperatures, in order to establish the effect of the mixing process and the range of temperatures within which the extruder could operate. The behaviour of the material at the lower temperature spectrum was found to relate to the process known as cold extrusion. Laboratory made model chocolate was subjected to reciprocating and capillary extrusion at different temperatures and analysed Theologically. The purpose was to assess the effect of extrusion on the rheological profile of the chocolate. It was established that the average viscosity was lower in chocolate that had been extruded at 25 °C, indicating that agglomerate breakdown took place more effectively where the material was extruded at a solid state. The results were compared to those of model chocolate subjected to mixing in an apparatus known as the Speed Mixer. The Speed Mixer was found to be a more effective method for agglomerate breakdown than extrusion. The size of the particles and agglomerates in chocolate during the various phases of conching was assessed with the help of particle size analysis. It was established that the early stages of the process are the most effective, as far as the breakdown of the agglomerates to their component particles is concerned. The experiments highlighted the difficulty in obtaining valid conclusions about agglomerate breakdown in a complex material such as chocolate. Agglomerate behaviour was usually extrapolated from related results, such as viscosity. In an attempt to draw more definite conclusions, a study of agglomerate behaviour under well defined stress conditions was evaluated, using characterised agglomerates in simple fluids. The system used sugar- based agglomerates in a sugar matrix, suspended in cocoa butter. The project had two main objectives. One was to assess the shape, size and strength of the agglomerates. The other was to study their level of breakdown when subjected to a mixing process similar to chocolate. The strength of the agglomerates was measured in two ways: Diametrical compaction and die pressing. The results of the two methods were not analogous, a possibility that has been established by past studies. The agglomerate and cocoa butter suspension was mixed in the RME, as well as with conventional extrusion of individual agglomerates and speed mixing and the extent of breakdown was investigated. The agglomerates were subjected to image analysis and four parameters of size (area, aspect ratio, roundness and equivalent diameter) were measured and analysed statistically before and after mixing. Area was found to be positively correlated to equivalent diameter, while roundness was positively correlated to aspect ratio. Despite its important role in chocolate mixing, temperature did not have a significant effect on agglomerate breakdown.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available