What is a cutting/shearing test?
In general, any texture analysis test that involves the use of a type of blade to perform the test, is performing a cutting or shearing action on the sample. A number of empirical fixtures feature a single blade or a number of blades which cut/shear through the sample, under specified conditions. The maximum force required and/or the work necessary to achieve this (i.e. the area under the curve) is taken as an index of firmness, toughness or fibrousness of the sample. Whilst empirical or imitative, shearing tests are very popular, particularly for the assessment of food texture.
Although the term shear is used to describe the action of such fixtures, an examination reveals that a complex pattern of forces is involved. Compression and tension forces are developed as well as shear. Thus results cannot be expressed in terms of shear moduli and can only be regarded as providing empirical comparisons of the resistance offered by samples to deformation under specified conditions.
Why perform a cutting/shearing test?
If you imagine that the teeth were pulled into a straight line, they would effectively be presenting a ‘blade’ edge. It makes sense, therefore, that any test where a measure of bite force is required, would involve the choice of a blade to perform the test. This test also measures a sample’s shear resistance force when being cut by a knife (such as during preparation and serving), which provides a good indication of tenderness and toughness.
Since most foods are viscoelastic rather than elastic and are usually subjected to large compressions in testing, the strict definition of Youngs modulus seldom applies to food materials and the term modulus of deformability is perhaps a better term. However, the concept of Youngs modulus of elasticity is frequently used to express the stress-strain ratio of the food, at least under moderately light compressions and in the area of the force-compression curve that is reasonably linear.
Compression tests can be carried out on a wide variety of viscoelastic products that experience such a force in natural conditions. These may include fruit and vegetables, puffed cereals, cakes and biscuits, confectionery and pharmaceuticals.
Properties that can be measured with a cutting/shearing test
Cutting/shearing tests are typically chosen to measure:
Bite force, firmness, toughness, shear force etc.
To understand how these properties are measured visit the Textural Properties page.
Typical probes and fixtures used for cutting/shearing tests
We are often asked why there are so many different blade fixture options available from Stable Micro Systems. Our range of blades vary considerably in size, material, thickness and sharpness. In general they are used to measure the Bite/Cutting Force of products which in some instances can relate to their ‘Toughness’. The following guidelines may help in clarifying the potential use of each.
Standard Blade Set (HDP/BS) – This is the most common choice for a cutting test and consists of reversible knife edge or guillotine edge and a Warner-Bratzler blade. It can be used with a slotted guide (for cutting all of the way through a sample). Whilst universal in its application the blade is not sharp and may therefore ‘compress’ fragile samples before the cutting action takes place.
Warner Bratzler Blade Set with ‘V’ slot blade (HDP/WBV) – As dimensionally specified for use in the USDA Standard for meat testing.
Warner Bratzler Blade Set with ‘Rectangular slot blade (HDP/WBR) – As dimensionally specified for use in the Danish Honikel method for meat testing.
Light Knife Blade (A/LKB) – A small Perspex blade which may be a cheaper alternative to the standard Blade Set but is universal and robust. Due to its material it may not withstand testing of hard products and can be more easily damaged if not cared for correctly.
Light Knife Blade (A/LKBF and F2) – Specifically dimensioned for use when performing the AACC Method 16-50: Cooked Pasta Quality/Firmness or AACCI 66-52-01. These blades do not tend to be used for any other method or sample type.
Asian Noodle Rig (HDP/ANR) – This internationally popular blade was developed after extensive work carried out at the Wheat Marketing Centre in Oregon, USA by Gary Hou and his team.
Meullenet-Owens Razor Shear Blade (A/MORS) – Developed initially for the assessment of chicken breasts. Tests using the MORS blade are conducted on whole intact fillets which minimises the experimental errors attributable to sample preparations, shortens sample preparation time and leads to a simpler testing solution. This method thereby provides advantages over existing poultry breast meat tenderness methods as it could significantly save labour, time and expertise to implement for routine quality control.
Craft Knife A/CKB) – Due to the sharpness of the blade, hard products can be cut whilst providing a ‘disposable’ blade option if blade blunting is of concern. The blade thickness enables precision cutting of very small samples, for example seeds or nuts, or shearing without compression of very soft or brittle samples such as laminated pastry. However due to its limited size only samples of up to 50mm wide can be tested and the depth of cutting is also limited.
Sharp blades are recommended for the testing of small, brittle or multi-layered products or hard products where a disposable blade is then suited.
Extended Craft Knife (A/ECB) – This blade was introduced due to the popularity of the standard craft knife and the necessity to use a thin disposable craft blade for the cutting of deeper and wider samples than could previously be accommodated. Samples of up to 100mm wide can be tested.
Volodkevich Bite Jaws (HDP/VB) – This fixture was developed to imitate the action of an incisor tooth biting through food. However, its popularity has declined due to its size which limits the sample cross-section of 1cm² unless the upper ‘tooth’ fixture is used on its own.
Wire Cutter (A/BC) – Wire-cutting devices have been used to measure fibrousness in asparagus and rhubarb, firmness and spreadability of butter, consistency of cheese and firmness of cottage cheese. One advantage of the use of wire-cutting devices is that the area of sample in contact with the wire is constant during a test and this reduces errors due to friction. Tests using a wire probe usually reach a plateau, which is chosen to characterise the cheese texture.
Fracture Wedges (A/WEG) – Fracture Wedges provides a means to assess cutting from both the top and bottom of the sample via an upper and lower wedge each with a cutting angle of 30° and 30mm width. The maximum sample width is however limited to 30mm.
For products with variable texture across their length, e.g. meat or cereal bars, results from single blade tests may be highly variable. This is because for one blade test of a cereal bar the blade may come into contact with e.g. a peanut and a chocolate chip, and the next blade test of the same bar may slice through a raisin and an apricot piece, thus the blade is almost testing different samples. In this case a Kramer shear cell is often used which performing a cutting/shearing test using 5 or 10 blades on the sample for each test. This provides an averaging effect and has shown to be more reproducible for highly variable samples.
Using multiple blades within a test is recommended for products with variable structure either due to nature (fruits, vegetables, meat) or design (breakfast cereals, cereal bars, pasta shapes).
Kramer Shear Cell (HDP/KS5/10) or Mini Ottawa-Kramer Shear Cell (HDP/MK05) – Different shapes and sizes of product present a sample which may be variable in configuration. Repeatable orientation for testing can be difficult when tested individually with a Blade Set. A Kramer Shear Cell or Mini Ottawa/Kramer Shear Cell provides the most suitable device for the testing of a non-uniform sample or one with variable geometry. A number of pieces or weight of sample is sheared ‘in bulk’ and the result is an average of the forces required to cut through the sample. The area under the curve is usually calculated and termed the ‘work of shear’ – a larger value indicating a firmer or tougher sample. The Mini Kramer Shear Cell is ideal for the testing of small sample pieces and reduces the volume of sample required for testing. Smaller forces are produced during the test whereas the Kramer Shear Cell may necessitate the use of a TA.HDplus Texture Analyser if the testing force exceeds 50kg.
Triple Ring Cutting System (A/TRCS) – This Cutting System allows the determination of the textural properties of small non-uniform samples in smaller bulk quantities and thereby requiring lower forces. It consists of an array of concentric cutting rings which provides a large cutting surface area in a relatively small device.
While the description of "shear testing" is commonly given to any test that uses a cutting action to apply stress to a food sample, the true definition of shear engineering does not use a blade, but refersto a material that is stressed from two opposite directions and then shears within its own structure.
Both the Bilayer Tablet Shear Rig and the Vertical Powder Shear Rig perform true shear tests where the powder or tablet are forced to shear within their structure.
To understand how these fixtures are designed and manufactured visit the Texture Analysis Attachments page.
Items with codes prefixed 'HDP/' must be used with the HDP/90 Heavy Duty Platform.
Items tagged * are Community Registered Designs.