(547g) Pipe Rheometry of Ice Cream

Recent research has quantified significant effects of viscous heating in ice cream flow along industrial pipelines. The microstructure of ice crystals, air bubbles, fat droplets and matrix is central to the physical and sensory properties of ice cream. Pipeline flows in factories tend to destroy the structure that has been carefully created in previous unit operations. However, viscous heating does offer a number of interesting and potentially valuable possibilities if it can be carefully controlled.

A new novel pipe rheometry rig for ice cream was designed and constructed. It is comprises of interchangeable pipes with different diameters that will be useful for monitoring viscous heating effects in each size of pipes. Special attention has been paid to accurate measurement of temperature since it was discovered that viscous heating is significant at a very low temperature during ice cream processing. Trials were also conducted to find a suitable model ice cream material. The purpose of these trials was to obtain a formulation that will yield a model ice cream which has similar properties with the real ice cream when deformed and to obtain a product that will last longer in comparison to real ice cream which can perish easily due to the inclusion of dairy material. Model ice cream made with vegetable oil, sugar and water of certain percentages was found to be the best substitute for real ice cream.

Pressure drop measurements were used to study the rheology of model ice cream as it flowed at -5^oC from an industrial freezer to the pipe rheometry rig. Electrical resistance tomography was implemented to non-invasively measure velocity profiles within the flow. The flow data from each size of pipe via pressure gradient were used to construct Bagley plots which enabled the wall shear stress to be compared to apparent shear rates. The data analysed with the classical Mooney method and Tikhonov regularisation which was used to back out flow curves indicated significant effects of viscous dissipation which is more pronounced at larger diameters. Similarly, flow curves were backed out of the directly measured velocity profile from ERT, enabling clear interpretation of apparent wall slip effects and robust material characterisation.

It is believed that the novel technology and the methods developed in the research could be used for the on-line control of ice cream flow and would benefit the ice cream processing industry by providing valuable information on the improvement of the process.