Liquid phase migration in the extrusion of icing sugar pastes

Liquid phase migration was found to affect the extrusion behaviour of 'soft solid' icing sugar pastes. Significant liquid drainage and apparent work hardening was observed with a simple aqueous liquid phase; the onset of phase migration with solutions of egg white in water was found to depend on the liquid phase volume fraction and the extrusion velocity. Flow visualization studies showed that work hardening was Linked to the growth of an internal static zone of drier material at the die entry. Consolidation experiments confirmed that liquid migration is likely to occur in these pastes. An initial hypothesis for the observed behaviour is proposed. The modified plasticity approach described by Benbow and Bridgwater(1) for modelling these pastes' extrusion behaviour was not successful as the characterizable pastes exhibited weak yield stress behaviour and strong velocity dependence.