Types of Tests

Texture (Chewiness, Spreadability, Stickiness)

Testing machines have found extensive use in the science of food technology in an attempt to quantify the physical characteristics of food materials. The usual methods, as for other materials are carried out.

Compression i.e. deformation testing, friability or fairy cakes, etc.

Shear i.e. the Warner - Bratzler shear fixture, extrusion etc.
Bending i.e. snap testing, brittelness etc.
Puncture i.e. Magness Taylor probes, skin toughness etc.

Often the methods are a combination of shear and compression as in the Kremer Shear Cell.

In every day use for the food technologist the normal terms such a E-Modulus, tensile strength shear modulus have little meaning and do not appear to be of much use. What is attempted are mechanical tests to try quantify the subjective oral and no-oral sensory judgements made about food stuffs, ripeness, tenderness, firmness, crispness, crunchiness, chewiness, freshness/staleness, scoopability, cookablity etc.

Measurements are also made to determine to the visco-elastic properties by cone penetration, extrusion and back extrusion. Many of these tests have been developed in conjunction with taste panels to correlate the numerical results to human acceptability and the sense of texture that people judge food stuffs. In an attempt to mimic the action of the human jaw the ‘Texture Profile Analysis’ has been developed which consists of a cycling test of two consecutive compression and tensile cycles often with a wait time between the two cycles. It is accepted this is far removed from the actual shear and compression forces experienced within the mouth, which moves in three dimensions at varying rates, but is extremely useful in determining constancy of product and in the development of new products. Sudo technical names are given to the results like cohesiveness, gumminness, etc. which would normally be unacceptable to the materials scientist. However by comparing the numbers produced with the taste panels these results bear some correlation to the subjective nature of food texture. Some more scientific names are also used which may have the same meaning to other material testing i.e. Modulus of Elasticity while others may have another meaning then that normally used i.e. Resilience.

Often the test methods are developed in Universities and the fixtures devised bear the name of the researcher or location giving an air of the exotic for which in practice may be quite a simple test.

II.e. The Ottowa Cell, Warner Bratzler, Volodkevitch Bite, Magness Taylor Probes, Kremer Shear Cell, FMBRA Standard Dough Pot Set, Chen-Hosey Dough Stickiness, Kieffer Dough forms and extensibility Rig, Dobraszscyk Roberts, Miller-Hoseney Toughness Rig etc.

Sometimes acoustic devices are attached to the specimens in an attempts to determine crunchiness and crispness and a formula for crispness has been suggested as

= -15.6 + 5.35NP + 133 MHP - 6.21P

where NP = number of sound peaks during one bite.

MHP = mean height of the peaks of the sounds.

P = maximum force as measured in a Kramer Cell.

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