Chocolates have a wide range of flow properties which relate to enrobing and making blocks. In the viscosity measurement of chocolate products, it is common to describe the flow properties using the Casson flow curve, which incorporates the following two parameters:
To measure the Casson values, it is necessary to take laboratory viscometer readings at different speeds in order to evaluate shear stresses against different shear rates. Calculations are then carried out to determine the Plastic Viscosity and Yield Stress values which can be used to define process viscometer set points for on-line process control.
Chocolate measurement typically utilizes the HADV-II+ PRO Viscometer and Small Sample Adapter (SSA) accessory in addition to the Brookfield TC-501 Circulating Bath. This instrument can accommodate a range of chambers and spindles; for chocolate, the recommended combination is an SC4-13R chamber with an SC4-27 spindle. When used with Brookfield's WingatherTM software for data gathering, the results can be plotted and the data further analyzed using a built-in mathematical model to calculate Casson parameters.
Before running this test, the chocolate must be properly prepared:
A sample of milk chocolate was analyzed in our laboratory to calculate a viscosity profile, as well as determining the Casson parameters of Yield Stress and Plastic Viscosity values. An up/down speed ramp was done from 2 to 10 rpm, giving a viscosity range from 127,750 to 45,750 cP, over shear rates from 0.68 to 3.40 sec-1. When the Casson model was applied to the data, the Plastic Viscosity was found to be 10,105 cP and the Yield Stress was 442.6 dynes/cm².
A more detailed package of information on measuring chocolate viscosity is available from Brookfield upon request.