Question

Why when you cool the egg down after cooking does it not become liquid again and why when you neutralize the pH of the cheese does it not become liquid milk again?

Answer 1

Cooking an egg causes proteins like albumin to denature and coagulate into a solid structure, which is irreversible upon cooling.

Step-by-step explanation:

The process of cooking an egg involves the denaturation of proteins, such as albumin, in the egg white. When you cook an egg, these proteins unfold and then coagulate, forming a solid structure. This change is irreversible because the new bonds and structures that form are stable and do not revert back to their original form when cooled. In the case of cheese, changing the pH alters the casein proteins, causing them to curdle and solidify. Neutralizing the pH does not reverse the chemical reactions that have occurred or the bonds that have formed, hence cheese does not revert back to liquid milk.

Regarding the egg denaturation, at temperatures above 373 K, the process is spontaneous, with the denaturation being driven by the formation of a disorganized solid, making it irreversible. Similarly, for cheese, altering the pH causes a change in the protein structure that cannot simply be undone by neutralizing the pH, as the material has fundamentally changed.