The Axisymmetric Extrusion of Solid Chocolate and the Effect of Die Geometry

Abstract

This paper investigates some of the effects of axisymmetric die geometry and flowrate during the isothermal extrusion of solid chocolate. Experimental observations, such as the material exhibiting a yield stress, flowrate independence and irreversible deformation, indicate that solid chocolate can be modelled using a rigid perfect plastic constitutive model (usually applied to the characterisation of metal forming processes). Numerically obtained extrusion pressures for a range of area reductions, using a commercial finite element package (ABAQUS) in combination with a remeshing code, are compared to experimental data to determine the uniaxial yield stress of the material. Analytical approximations are used to verify the numerical results. A study of the material behaviour in the die land, however, shows that the perfect plastic description can be inadequate in predicting extrusion pressures under certain conditions.

Effect of thermal and mechanical rejuvenation on the rheological behavior of chocolate

“…The solid particles suspended in the continuous phase may form space spanning percolated network or simply get jammed owing to high solid content 12 . Application of deformation/ flow field either breaks the structure or induces unjamming, causing yielding of the same 1,4,13,[15][16][17][18][19] . Application of deformation field, therefore, causes alteration of structure, a property that has been termed as rejuvenation, a behavior commonly reported for polymeric glasses [20][21][22] , colloidal glasses and gels [23][24][25][26][27] .…”

“…Crystalline moieties of the cocoa butter, if present, may also become part of the network along with particulate matter 28 . Application of deformation field breaks the physical cages as well as the network (if any), inducing fluidity in the chocolate 1,[17][18][19] , a behavior typically observed in thixotropic materials 38,43,44 . Such reduction in viscosity of the chocolate with time under application of deformation field (under isothermal conditions) is seemingly comparable to the reduction in viscosity with time caused by an increase in temperature.…”