International inter-laboratory trials to determine the factors affecting the measurement of chocolate viscosity

The working group of the International Office of Cocoa, Chocolate and Sugar Confectionery (IOCCC) performed a sequence of five ring tests to improve the agreement of the standard method for measuring viscosity of chocolate between laboratories. Reporting shear stress measurernents instead of using the Casson equation improved the agreement, as did standardising the method of cleaning the concentric cylinder and calibrating the viscometers. In the revised method, the standard deviation for shear stress measurement at shear rates greater than 5 s(-1) from 23 laboratories was less than 8%. However, the Casson yield values had a seven-fold range and the Casson plastic viscosity a two-fold range, which was unacceptably high. A new method (IOCCC 2000) has been published as a result of this work and is available from CAOBISCO in Bruxelles, Belgium.