Investigating the shear rheology of molten instant coffee at elevated pressures using the Cambridge multipass rheometer
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The processing of instant coffee may involve pumping the material in a melt phase through operations at elevated pressures. The shear rheology of this material was investigated using the Cambridge multipass rheometer, which allows for shear rheometric testing under conditions of independently controlled temperature and pressure. In this work the back pressure was set to dissolve any air that was present in the melt, so that the rheology of the single phase material could be tested. Data were collected over the accessible range of conditions; shear rates from 0.01 to 1000 s −1 , temperatures from 80 to 110 °C, and pressures from 0.01 to 300 bar. The melt exhibited thixotropic behaviour at low shear rates, and the data could be fitted to a non-dimensionalised Carreau fluid model with a temperature dependence which followed an Andrade relationship. Sample to sample variation was observed, which is attributed to differing water content. The results demonstrate how the rheology of complex food materials can be accessed under process conditions.
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1744-3571