Characterisation of Pastes in Chocolate Processing

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Iosson, Charlotte (2019). Characterisation of Pastes in Chocolate Processing. University of Birmingham. Eng.D.

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Abstract

The initial process step to combine the ingredients that form chocolate, prior to refining of the particle size, produces a thick paste resembling wet sand. Currently, experienced operators are relied upon to assess differences between batches. Pastes containing high volumes of large particles are challenging to measure using existing rheological techniques. A back extrusion technique is developed which produces comparable measurements of pastes containing small particles to existing rheological techniques. Repeatable measurements have also been achieved of chocolate pastes, containing 74 vol% solids up to 1000 µm. These chocolate pastes display shear thinning behaviour and many exhibit a yield stress. Increasing the fat content reduces the yield stress and shear thinning behaviour, generating a paste with properties closer to a Newtonian fluid. Increasing the temperature of the paste also reduces the overall paste viscosity and refining warmer pastes produces smaller particles, similarly to increasing the fat content. Measuring the power draw of the mixer, although specific to the mixing geometry, provides an indication of differences between pastes which correlate with viscosity measurements. Additionally, the particle size of the refined material correlates strongly with the power measured on the refiner rolls, offering a supplementary method of assessing the particle sizes online.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

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