1. Physical phenomena

The physical mechanisms of internal transfers are described in two stages: firstly, the two fundamental mechanisms in the fluid phase, i.e. ordinary diffusion and convection, and then the mechanisms specific to solid foods, with emphasis on the role of water.

Generally speaking, the transfer of matter and heat tends to re-establish the thermodynamic and mechanical equilibrium of a system. The driving forces behind these transfers are the gradients of the intensive physical quantities characteristic of equilibrium, generally referred to as potentials. A gradient is a measure of the variation of a quantity in a given direction in space. It is commonly represented by the partial derivative of this quantity with respect to the coordinate in the direction considered. Strictly speaking, the gradient is a vector obtained from a scalar by applying the differential operator...