Study of the rheological behaviour of chocolate
Mélanie Bécu, Joan Rius Fonoll, 1Sophie Liégeois, Benoît Haut, Frédéric Debaste Transfers, Interfaces and Processes (TIPs) –Chemical Engineering Unit, Université Libre de Bruxelles, Av. Franklin Roosevelt, 50 CP 165/67 B-1050 Brussels, email: mbecu@ulb.ac.be; 1 Chemical Engineering Department, Institut Meurice, Institut Meurice, Av. Emile Gryson, 1 B-1070 Brussels, Belgium. Introduction In the food industry, the production process is often established in an empirical way, according to rules of good practice. These methods present gaps, in particular at the level of the production regularity. To model and optimize the process, it is highly useful to determine the physico-chemical properties of the product. In this work, chocolate is studied, aiming direct industrial application and a general enhancement of rheological mechanism understanding. Indeed, the chocolate is a suspension of aggregative solid particles in cocoa butter. Rheological behaviour of this fluid is therefore relying on different key phenomena. In this work the flow behaviour of chocolate is characterized and an attempt of a mathematical model is developed. The applied, industrial, goal is to model the tempering process. Tempering is an important step in the process to obtain a quality product. A temperature programme is applied to chocolate to lead to a good crystallization, which is the usual tempering process. A well tempered chocolate have a good snap, is shiny and can be well preserved. The tempering process is affected by many parameters such as viscosity, shear rate, particle concentration, and thermal history. For example it is possible to induce a good crystallisation by a high shear rate [1]. To improve this process, a better understanding of the rheological behaviour and the physical properties of liquid chocolate is required. Chocolate is a suspension of solids particles (cocoa, sugar and milk powder) in a continuous fat phase. It is a