skip to content

Department of Chemical Engineering and Biotechnology

Yu Wen Chen

Cold Extrusion of Flexible Chocolate



Cold extrusion of flexible chocolate is concerned with pressure driven extrusion processing of chocolate in the semi-solid state. Contrary to the traditional liquid melt processing of chocolate, Beckett et al. [1] showed that the semi solid ram extrusion processing of chocolate below the melting point of the material was feasible. The fresh extrudate was found to have a temporary flexibility before becoming brittle with storage time. This short term flexibility of the extrudate enables for instance complex shape formation immediately after extrusion.

The picture shows a cold extruded chocolate filament being tied into a knot. Different complex shapes and sizes can be made under various extrusion processing conditions.

Extruded chocolate filament tied into a knot

Wide Sheet Extrusion

The wide sheet extrusion of flexible chocolate was performed using a converging diverging die and a Betol ram extruder.

Chocolate buttons or granules are fed into the barrel and the chocolate is then extruded through the die to form flexible sheets. The shape and size of the sheets was altered using different die designs and geometries.

Extrusion of chocolate sheet


After extrusion, the flexible chocolate sheet was further shape formed by stamping using a male and female mould. The desired quality of the final product (e.g. shape definition, surface gloss) could be controlled by careful adjustments of both extrusion processing and stamping parameters.

Stamping chocolate sheet


The stamping process was modelled using Forge 2D, which is commonly used to study plastic flow in metal processes such as extrusion and forging. This allowed useful predictions of the stress (shown in the diagram to the left) and strain distributions during material deformation as well as the amount of mould fill and stamping load involved.

Modelling of chocolate sheet stamping




































1. Beckett, S.T., Craig, M.A., Gurney, R.J., Ingleby, B.S., Mackley, M.R. and Parsons, T.C.L., The cold extrusion of chocolate, Trans IChemE, Vol. 72, Part C, p. 47-54 (1994).

Return to the main Alumni page