Rheology of cocoa butter

The rheology of beta(V/VI) cocoa butter crystal melt suspensions (CB CMS) was investigated directly after crystallization using in-line capillary rheometry (UVP-PD) as well as after tempering at zero deformation using off-line capillary rheometry (CR) and rotational rheometry (RR). CB CMS thixotropy was quantified by RR revealing that structure build up processes at zero deformation were not at equilibrium after 18 h, whereas structure decay occurred mainly in the first 10 s of measurement at (gamma) over dot = 60 s(-1). CR and UVP-PD were identified as preferable methods to probe thixotropic materials due to the short measurement time t(M) and uniform sample deformation history for every (gamma) over dot-step. The scaling of the relative viscosity eta(rel) and the (apparent) yield stress tau(0)/tau(app)(0) as function of deformation history revealed two different regimes. Directly after the crystallization, the CB CMS behaved like a suspension of anisotropic crystals with a fractal dimension D approximate to 1.57, an intrinsic viscosity [eta] of 20 and a maximal packing fraction Phi(max) of 0.17 leading to a scaling of eta(rel) = (1 - (Phi(SFC)/Phi(max)))(-3.4). After tempering at zero deformation, crystal aggregation increased the fractal dimension to D = 2.6 and the scaling of the relative viscosity eta(rel) reduced to similar to Phi(2)(SFC), analogously to a jammed system of elastic particles.