Tester uses extrusion method to measure viscosity

By Ahmed ElAmin

- Last updated on GMT

Related tags: Viscosity

An extrusion-style tester provides an economical alternative when
measuring the dynamic viscosity of foods, its manufacturer claims.

Viscometers are used by the food industry to ensure the consistency and quality of liquid foods.

Zwick Roell claims its new tester provides what the company claims is an economical alternative to using rotation viscometers, when testing such foods as chunky fruit preparations or yogurts with fruit pieces. The process can be used for tests of foods already in a container.

The backward extrusion fixture apparatus tests for viscosity based on the principle of using the displacement of the test foods material through the ring-like gap between a piston and a test cell.

The cell is filled with the test substance and the piston is lowered into the container, pressing the material up through the annular gap. When the piston is raised, the material flows back through the annular gap into the cell.

By contrast, rotation viscometers measure using a rotational body that is submersed into the testing material. A rotor rotating at a constant speed is immersed in the fluid to be tested. The fluid's resistance to the rotation is a measure for the viscosity of the fluid.

The Zwick Roell system allows food testers to repeat the cycle as often as needed using adjustable shear rates, the company claimed. The test can be adapted to the test material, and the viscosity can be measured across the entire shear range with a single test.

The user can select different dimensions of piston depending on the test substance. The method allows testing directly in the container during production, for example, in a bucket or cup.

The material does not need to be pre-stressed by decanting prior to the test. If the food makers wants to allow for the continuous pre-stressing of the material, the included software can be programmed to automatically apply pre-stress under constant conditions.

The flow effects that take place in production systems can be reproduced by varying the tester's annular gap and piston speed.

The software, called testXpert II, allows users to collect data and perform the evaluation using graphical displays and documentation. Each cycle of testing can be run with a different shear rate. Testing parameters can be modified and the equipment's settings can be stored for each type of configuration.

The parameter storage allows a simple exchange of the test setup in the texture testing machine without having to re-measure the test cell.

Zwick is a division of the Zwick Roell Group based in Ulm, Germany.

Related topics: Food Safety & Quality

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