Food Rheology

Food fluids have have a wide range of flow properties. These properties vary by food type and by manufacturer and by batch to batch. Process controls are employed to ensure that a given level of consistency is achieved. In terms of material characterisation, this leads to two major questions :- 1. What is the rheology of this particular food fluid ? and 2. What has changed between batches ?
Low viscosity fluids can generally be adequately characterised by a viscosity measurement. As the fluid becomes more viscous and less Newtonian, then it is more desirable to have shear viscosity curves rather than a viscosity. For spraying the most desirable measurement is the extensional viscosity at the same conditions as the process. We can also model a process and show the relevant changes that can be expected from a change in viscosity.

Going about the job of testing.

Testing always can be classified as either 1. We don't know what it is, and we're finding out about it. or 2. We know what it should be, and we're just checking. The first kind of testing requires some time to check on the fundamentals - is the flow stable? is the temperature optimum ? does it degrade? is it repeatable ? is there significant inhomogeneity ? The second kind of test is generally referred to as QC testing, where we simply repeat what we did before.

Testing for processability should generally be done at rates, pressures and temperatures that resemble those found in the process. For this kind of work, we will generally recommend a capillary rheometer or an extruder. For fundamental chemistry, will generally recommend a rotational rheometer. We can supply results as raw data, or as a model. We can also supply calculated and CFD models of the flow in a process.