Shear Rheology of Molten Crumb Chocolate

Authors

  • J.E. Taylor,

    1. Authors Taylor, Johns, Routh, and Wilson are with Dept. of Chemical Engineering and Biotechnology, New Museums Site, Pembroke St., Cambridge, CB2 3RA, U.K. Author Van Damme is with Mars Chocolate, Dundee Rd., Slough, SL1 4JX, U.K. Direct inquiries to author Wilson (E-mail: diw11@cam.ac.uk).
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  • I. Van Damme,

    1. Authors Taylor, Johns, Routh, and Wilson are with Dept. of Chemical Engineering and Biotechnology, New Museums Site, Pembroke St., Cambridge, CB2 3RA, U.K. Author Van Damme is with Mars Chocolate, Dundee Rd., Slough, SL1 4JX, U.K. Direct inquiries to author Wilson (E-mail: diw11@cam.ac.uk).
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  • M.L. Johns,

    1. Authors Taylor, Johns, Routh, and Wilson are with Dept. of Chemical Engineering and Biotechnology, New Museums Site, Pembroke St., Cambridge, CB2 3RA, U.K. Author Van Damme is with Mars Chocolate, Dundee Rd., Slough, SL1 4JX, U.K. Direct inquiries to author Wilson (E-mail: diw11@cam.ac.uk).
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  • A.F. Routh,

    1. Authors Taylor, Johns, Routh, and Wilson are with Dept. of Chemical Engineering and Biotechnology, New Museums Site, Pembroke St., Cambridge, CB2 3RA, U.K. Author Van Damme is with Mars Chocolate, Dundee Rd., Slough, SL1 4JX, U.K. Direct inquiries to author Wilson (E-mail: diw11@cam.ac.uk).
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  • D.I. Wilson

    1. Authors Taylor, Johns, Routh, and Wilson are with Dept. of Chemical Engineering and Biotechnology, New Museums Site, Pembroke St., Cambridge, CB2 3RA, U.K. Author Van Damme is with Mars Chocolate, Dundee Rd., Slough, SL1 4JX, U.K. Direct inquiries to author Wilson (E-mail: diw11@cam.ac.uk).
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Errata

This article is corrected by:

  1. Errata: Erratum Volume 74, Issue 4, vii, Article first published online: 4 May 2009

Abstract

ABSTRACT:  The shear rheology of fresh molten chocolate produced from crumb was studied over 5 decades of shear rate using controlled stress devices. The Carreau model was found to be a more accurate description than the traditional Casson model, especially at shear rates between 0.1 and 1 s−1. At shear rates around 0.1 s−1 (shear stress approximately 7 Pa) the material exhibited a transition to a solid regime, similar to the behavior reported by Coussot (2005) for other granular suspensions. The nature of the suspension was explored by investigating the effect of solids concentration (0.20 < φ < 0.75) and the nature of the particles. The rheology of the chocolate was then compared with the rheology of (1) a synthetic chocolate, which contained sunflower oil in place of cocoa butter, and (2) a suspension of sugar of a similar size distribution (volume mean 15 μm) in cocoa butter and emulsifier. The chocolate and synthetic chocolate showed very similar rheological profiles under both steady shear and oscillatory shear. The chocolate and the sugar suspension showed similar Krieger–Dougherty dependency on volume fraction, and a noticeable transition to a stiff state at solids volume fractions above approximately 0.5. Similar behavior has been reported by Citerne and others (2001) for a smooth peanut butter, which had a similar particle size distribution and solids loading to chocolate. The results indicate that the melt rheology of the chocolate is dominated by hydrodynamic interactions, although at high solids volume fractions the emulsifier may contribute to the departure of the apparent viscosity from the predicted trend.

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