Egg-speriments: Stretch, crack, and spin

TL;DR

This paper explores the physical and rheological properties of egg whites through experiments involving stretching, cracking, and spinning, revealing insights into their visco-elastic behavior, anisotropic crack patterns, and internal flow dynamics.

Contribution

It introduces novel experimental methods to analyze egg white properties, linking rheology, crack patterns, and spinning behavior to internal protein structures and flow characteristics.

Findings

Egg white exhibits shear-thinning and visco-elastic properties.

Long protein chains influence crack anisotropy in dried films.

Residual spin indicates internal flow damping related to viscosity.

Abstract

Eggs are key ingredients in our kitchens because of their nutritional values and functional properties such as foaming, emulsifying and gelling, offering a wide variety of culinary achievements. They also constitute ideal objects to illustrate a myriad of scientific concepts. In this article, we focus on several experiments (egg-speriments) that involve the singular properties of the liquids contained inside the eggshell, especially the egg white. We first characterize the rheology of an egg white in a rotational rheometer for constant and oscillatory shear stresses revealing its shear-thinning behavior and visco-elastic properties. Then, we measure the tendency of the fluid to generate very long filaments when stretched that we relate to the shear modulus of the material. Second, we explore the anisotropic crack pattern that forms on a thin film of egg white after it is spread on a surface and let dried. The anisotropy results from the long protein chains present in the egg white which are straightened during film deposition. Finally, we consider the "spin test" that permits to distinguish between raw and hard-boiled eggs. To do so, we measure the residual rotation of a spinning raw egg after a short stop which reflects the continuation of the internal flow. These observations are interpreted in terms of viscous damping of the internal flow consistently with the measurements deduced from rheology.