Starting situation: Current investigations on own pralines at the IVV and the experience with the IVLV project "Pralines" provide interesting information on the correlation of contact intensity between filling and shell and the later tendency to fat bloom formation. If there is a mechanically firm contact between filling and chocolate shell in the fresh product, increased fat migration and fat bloom can be expected; with weak contact, the shelf life seems longer. Both the production of the chocolate shell (process and speed) and the nature of the filling (tempering, temperature) influence the contact intensity. This observation is in line with the Fickian diffusion law:
m_t/m_S ≈(K √(D∙t))/d
The equation contains a constant K, which describes the contact intensity between both layers with values between 0 (= no contact) and 1 (= 100% contact). In addition, D = diffusion constant, t = time, d = thickness of the chocolate layer determine the migration in the form of m_t = migrated quantity at time t related to m_S = maximum migrated quantity at saturation.
A force-displacement measurement (tensile test) is used to measure the contact intensity. Experience gained on how to measure adhesive forces on packaging at the IVV is used for this purpose. First, a sample holder must be developed with which different scenarios in production (liquid filling meets solid chocolate and vice versa) can be simulated. Once this measuring method has been established, the influencing factors on the contact intensity can be examined more closely. Model chocolates are then produced and stored with the knowledge of the influencing factors. Production includes cold-formed chocolate shells, which are filled with a fat-based filling at various times after production, as well as completely crystallized chocolate bars, which are heated and brought into contact with a fat-based filling layer. The filling can also be varied by tempering (by seeding) and temperature during processing. The production is controlled by the solid fat content (SFC) measured with a NMR and melting curves obtained by DSC. The model chocolates are then stored and examined during storage for migration (NMR and GC) and fat bloom formation (DigiEye – WI).