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Extrusion test methods

Animation of back extrusion method

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.

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Test procedures

For example, sour cream, when not processed properly, can be grainy. By forcing sour cream through a small orifice – using forward extrusion- one will either see a smooth force level or a jagged one. The jagged one happens when the grains alternately become plugged and unplugged in the orifice building then releasing back pressure.

Back extrusion is a more common method of extrusion testing. The key factor to consider in back extrusion is the gap between the piston and the cylinder. This is called the “annulus” and the smaller the annulus, the greater the resistance to the flow.

For consistency in testing of viscous liquids, once decanted, samples should be left to recover structure in a controlled environment.

Extrusion testing fixtures

Extrusion test methodsExtrusion test results comparing firmness of yogurtsExtrusion applications in food industries

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The University of Arizona’s Nutritional Sciences Food Lab acquired a Texture Analyzer from Food Technologies about 5 years ago. The company has a great product, which is tailored to food needs. 

We have used the Texture Analyzer for both research projects and as a tool to demonstrate to students how food manufacturers can employ objective testing in product evaluation to show how differing ingredients in the same product can affect quality attributes. Its use adds another dimension to the foods labs.

Drew Lambert has been instrumental in helping with set up for testing and providing support whenever there’s a question. He has been a pleasure to work with and is always accommodating with our needs and schedules.  He has even sent us special attachments for special projects.  We couldn’t ask for a better technical support.  Thanks for a great product and great service.

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Steve Antonius, Del Monte Foods
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As a Meat Scientist and program leader for the University of Nevada, Reno, I need to ensure that equipment I use in my lab is reliable, durable, versatile, and accurate. For texture analysis of meats, there are many systems available in the market. Over the last 15 years of my career, I¹ve worked with many of them and had great and bad experiences with different brands.

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Amilton de Mello
Assistant Professor of Agriculture, Meat Science and Food Safety
https://www.unr.edu/anvs