Inside the shell of an egg is egg white that encircles egg yolk - VCE - SSCE Chemistry - Question 7 - 2020 - Paper 1

Vinegar is often added to the water when poaching an egg for several reasons related to its chemical properties.

1. Denaturation of Proteins: The egg white primarily consists of proteins, which undergo a process called denaturation when heated. Vinegar, being an acid (acetic acid), helps to lower the pH of the water, which can accelerate the denaturation process. When proteins denature, they unfold and coagulate, forming a solid structure around the yolk.

2. Surface Protection: The acid in vinegar allows the egg white to solidify more effectively around the yolk. When eggs are cracked into hot water, the outermost part of the egg white can dissolve into the water. The vinegar helps to coagulate this outer layer quickly, thereby keeping the yolk intact and preventing the egg from becoming too watery.

3. Maintaining Runny Yolk: By promoting quicker coagulation of the egg white, vinegar ensures that the egg white sets nicely without overcooking the yolk inside. This is essential for achieving a perfectly poached egg with a runny yolk, as it allows the yolk to remain soft while the white is firm.