Rheology of cocoa butter

The rheology of βV/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 γ˙ = 60 s−1. CR and UVP-PD were identified as preferable methods to probe thixotropic materials due to the short measurement time tM and uniform sample deformation history for every γ˙-step. The scaling of the relative viscosity ηrel and the (apparent) yield stress τ0/τ0app 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≈1.57, an intrinsic viscosity [η] of 20 and a maximal packing fraction Φmax of 0.17 leading to a scaling of ηrel=(1−(ΦSFC/Φmax))−3.4. After tempering at zero deformation, crystal aggregation increased the fractal dimension to D=2.6 and the scaling of the relative viscosity ηrel reduced to ~ΦSFC2, analogously to a jammed system of elastic particles. [Display omitted] •In-line and off-line rheology of CB CMS.•Quantification of thixotropic time scales relevant in CB CMS.•Mastercurves for the relative viscosity ηrel and the Herschel-Bulkley parameters τ0/τ0app,n,andK..•Fractal dimension and intrinsic viscosity of CB CMS.•Single crystal AFM image of CB CMS.