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Compression is one of the most common texture tests, especially for food products. Typically a sample is placed on a flat surface and an upper compression platen is lowered into the sample. For a true compression test, the compressed sample is never smaller in diameter than the two compression surfaces. Test are performed by compression to a given force, a given position or a percentage of the original height of the sample. Compression with smaller diameter probes, compress locally and may also induce penetration or puncture.
See FTC's compression test method capabilities.
TPA or Texture Profile Analysis, is a specialized derivative of compression testing. TPA consists of a 4 step test of compression, relaxation, recompression and then a final relaxation. A set of mathematical equations are then used on the resulting data to arrive at numerical values of such texture attributes as hardness, cohesiveness, springiness and chewiness. Compression testing can also be useful in measuring the adhesive or stickiness of the product. It is common in stickiness measurements to compress to a preset degree, hold the position for a given amount of time, and then pull back up quickly to accentuate the adhesive result.
Click here for a video demonstrating compression testing of cheese
The measurement of succulence (juiciness) is also performed by compression, the sample usually measure in bulk. Typically a constant force is applied for a given time and the expressible moisture is measured in a graduated cylinder.
Compression platens come in many different sizes and are made from various materials such as stainless steel, aluminium and plastics. Selection of the proper variant depends upon the product and the test sample's geometry.