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    Rheology of chocolate. Rheological studies of chocolate in relation to their flow and mixing properties during manufacture.

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    Publication date
    2010-01-21T15:21:27Z
    Author
    Rutson, Sandra M.
    Supervisor
    Benkreira, Hadj
    Beckett, S.
    Keyword
    Chocolate
    Manufacture
    Rheology
    Flow
    Mixing
    Work input
    Hysteresis
    Shear thinning
    Viscosity
    Rights
    Creative Commons License
    The University of Bradford theses are licenced under a Creative Commons Licence.
    Institution
    University of Bradford
    Department
    Postgraduate School of Studies in Chemical Engineering.
    Awarded
    1989
    
    Metadata
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    Abstract
    An investigation has been carried out into the rheology of chocolate in relation to its flow and mixing features in a real industrial environment. The chocolate manufacturing plant of Rowntree at York provided a base for this study. The project aims were: a) to measure the viscous and time dependent properties of chocolate. b) to explain the observed flow properties in relation to the constituents of chocolate. c) to determine the shear rate which, for a given recipe, yields a minimum stable viscosity (of particular commercial value). d) to assess the type of mixer able to provide this duty. The experimental work involved rheological studies with concentric cylinder and tubular viscometers, operated to measure viscosity as a function of shear rate and shearing time. The chocolate samples studied were taken from various points in the manufacture process at Rowntree, York. Model chocolate systems were made from cocoa liquor, and sugar with cocoa butter, which were studied to underpin the basic mechanisms of the flow properties of the total chocolate. Shear thinning in milk chocolate has been shown to be accounted for by surface coating and fat release from the cocoa cellular material. Analysis of the sugar and cocoa butter system gave large hysteresis loops which may be explained as due to agglomeration of the sugar particles. The level of hysteresis was found to be related to the polarity of the liquid phase, such that a more polar fluid results in less hysteresis. Laboratory experiments have revealed that the level of work input to give permanent viscosity reduction for milk chocolate is dependent on the measuring shear rate. The level of optimum shear input for the measuring range 10 to 130 sec 1 is 645 sec for 30 minutes. The apparent viscosity measured at lower shear rates requires much longer ([approx]100 minutes).
    URI
    http://hdl.handle.net/10454/4200
    Type
    Thesis
    Qualification name
    PhD
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    Theses

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