Foods are physicochemical systems in which a number of phases and chemical compounds can coexist in a metastable condition (that is, far from true thermodynamic equilibrium), and in the presence of microbes, whose metabolism may cause significant modifications of the chemical composition and physical properties of the hosting product. For this reason, food science not only deals with protection from external chemical, physical, and microbial injuries (for example, through the use of suitable additives or packaging), but also investigates the intrinsic causes of food instability, such as phase separations of dispersed systems, phase transitions (which mainly concern food polymers, such as starch, gluten and other proteins, and fats), enzymatic reactions (often related to the “endogenous” microbial agents), and preparation procedures (such as cooking, extruding, and freezing), all of which can profoundly modify the nutritional and sensory properties of the product.