E42 Plasticity - Meat

Topic

Meat is a complex biomechanical material whose texture, hardness, juiciness, and chewiness depend on the structure of its muscle fibers, collagen, and fat. Unlike the recoverable elastic behavior seen in bread dough—another model within this category—the plasticity of meat refers to permanent deformations that do not revert after cutting, biting, or crushing. When meat deforms beyond its yield point, the resulting deformation becomes permanent rather than recoverable.

The Von Mises criterion defines this yield point—the stress level at which the meat begins to undergo permanent deformation. While the Von Mises criterion is the standard model for isotropic materials (which lack a preferred internal direction), the anisotropy of muscle fibers means that the yield point in meat depends on the orientation of the cut applied to it. Consequently, the yield point differs depending on whether the cut is made parallel to the muscle fibers or perpendicular to them.

The yield point of meat drops drastically as the cooking temperature increases. Within a specific cooking temperature range, the meat's collagen denatures and begins to convert into gelatin via hydrolysis, significantly softening the meat. An Arrhenius relationship captures this dependency of the yield point on cooking temperature: higher cooking temperatures result in a lower yield point—according to the Arrhenius relationship—thereby making the meat more tender. The Warner-Bratzler test is the industry standard for measuring meat tenderness: a triangular-bladed shear cuts through a cylindrical sample, and the peak force required to complete the cut is measured; a peak force below a low threshold indicates tender meat, whereas a peak force above a higher threshold indicates tough meat. Because the meat's yield threshold—already reduced by the cooking temperature—is lower, the peak force measured by the Warner-Bratzler test is consequently lower as well.

Thus, this model—incorporating the yield threshold and the Warner-Bratzler test—ensures that the meat's fracture energy (the area under the stress-strain curve up to the point of rupture) reflects perceived chewiness: high fracture energy implies that more masticatory work is required to break the meat down completely. Meat cooked thoroughly at a low temperature for an extended period consequently exhibits lower fracture energy than the same meat cooked differently; this is because the collagen hydrolyzes at the sustained low temperature without causing the protein fibers to toughen, as would happen with more aggressive cooking methods. Prolonging the cooking time at this low temperature leads to greater collagen hydrolysis, thereby resulting in lower fracture energy.

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