Explorations in Chocolate Texture

Enric Rovira (chocolatier) and Ingrid Farré (Alicia Foundation)
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Public Lecture 04 (2012)
Key Lesson: Texture. The way that food feels in your mouth, independent of its taste, can be explained in terms of the bonds holding the molecules together.
The previous week showed some of the types of phase changes that occur when cooking food. This week master chocolatier Enric Rovira demonstrates the transformations that can occur in chocolate: from a cocoa bean to artistic sculptures. Ingrid Farré, from the Alicía Foundation, demonstrates some innovative ways to create textures in a cake. describes some ways to measure certain aspects of the texture or consistency of a food.




Overview of the Science

A spring is a useful analogy for describing the texture of food.
  • Calculate the elasticity of a material, based on physical measurements of its deformation.
    • The stress of a material is equal to the force applied to a material, divided by the area.
    • The strain of a material is a dimensionless way to describe the amount of deformation.
    • The elasticity of a material is equal to the stress divided by the strain. Stiffer materials, which are more elastic, require more force for the same deformation.
  • Calculate how the elasticity of a material scales with changes in the bonds at the microscopic level.
    • The elasticity of a material is due to energy stored in the bonds between its molecules. More energy can be stored by increasing the density of bonds, or the energy stored in each bond. For a gel, the energy is roughly equal to thermal energy (kBT). The density of the bonds is equal to the reciprocal of the cross-link spacing, l, cubed:

      $$ E = \frac{k_B T}{l^3} $$

      When l = nm and T = °C, then the elasticity is kPa.

  • Draw an approximation of how the microscopic structure of food changes when its elasticity changes.
    • Extra firm tofu has a smaller cross-link spacing than silken tofu.
    • Well-done steak has a smaller cross-link spacing that rare steak.
    • The elasticity of a gel is inversely proportional to the density of cross-links.