Physical Chemistry of the Egg-and-Lemon Sauce

This is a structural examination of egg-and-lemon sauce (avgolemono), a complex colloidal food which, depending on the stage of preparation and use, is a viscous liquid, an aggregated dispersion, a foam, an emulsion, and a gel. Following the food’s preparation, the pH-dependent zeta potential and phase equilibria/separations are discussed as principal contributors to the extensional rheology and to the relaxation times of its macromolecular components. Foaming under whipping is discussed along with the topology of the foam’s interface. These are used to understand the foam stability of the sauce, as it undergoes structural (foaming), compositional (addition of yolk), and chemical changes (acidification by lemon juice). The effect of the above on the shear rheology of the bulk phase and of the foamed product are used as to explain its foaming ability and stability. The foams are examined as to highlight the fine interplay of the dual character created by the bubble collapse and the liquidification during the recipe’s preparation. The temperature changes during the making and the application of the sauce, as well as cases of the recipe’s mismanagement (e.g. overheating), are discussed in terms of thermodynamics and structure.