Extrusion testing has many applications within the food, and other industries, for texture assessment. This method is relevant to semi-solids or viscous liquids, 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 test sample is placed into a confined container and then forced through an orifice or grid.
The foods resistance to this extrusion is then measured. 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 with the product being measured is placed in an open top cylinder, and a piston with a diameter smaller than the cylinder, is forced down into the sample.
The result is that the product flows back between the space created by the piston and the cylinder.