Extrusion testing has many applications for texture assessment within the cosmetics, pharmaceutical and food industries.
This method involves testing the compressive strength properties of semi-solids or viscous liquids, such as creams or gels, where the rheological properties of the product affect the flow.
Extrusion can be divided into two categories; forward extrusion and back extrusion.
Forward extrusion is when the semi-solid sample is placed into a confined container and then forced through an orifice or grid.
The compressive resistance to this extrusion of the semi-solid is then measured as it passes through the grid. The size of the orifice or grid selected is dependent upon the product being measured and the textural property of interest.
Back extrusion is typically performed using an open top cylinder containing the product to be measured. A piston with a diameter slightly smaller than the cylinder is forced down into the sample. This causes the product to flow back between the space created by the piston and the cylinder.
By using a force testing system to record the force vs displacement data on a graph, it is possible to analyse the curve to identify whether the semi-solid passes smoothly through the orifice or if it has jagged areas, indicating poorly processed materials.