What does boiling do to an egg?

1. Coagulation of Protein: The most noticeable change is the coagulation of egg proteins. Egg white (albumen) is mostly composed of water and proteins, primarily ovalbumin and globulins. When the egg is heated, these proteins start to coagulate, or solidify, causing the white to turn from transparent to opaque. Coagulation occurs around 175°F (80°C).

2. Yolk Changes: The egg yolk also undergoes changes during boiling. It contains a high concentration of fat and proteins. As the egg is heated, the yolk proteins start to coagulate, but the fat prevents the yolk from becoming completely solid. The yolk's color may also change from a light yellow to a deeper, more orange hue due to chemical changes in pigments.

3. Formation of Air Pockets: As the egg heats, the air inside it expands. This causes the formation of air pockets or cavities within the egg white. These pockets are often visible when you peel a hard-boiled egg. The larger air pocket at the rounder end of the egg is sometimes referred to as the "air cell."

4. Denaturation of Enzymes: Enzymes are proteins that catalyze chemical reactions in living organisms. When the egg is heated, these enzymes are denatured, meaning their structure is altered, and they lose their ability to function. This process contributes to the changes in the egg's texture and consistency.

5. Development of Chalky Yolk: Overcooking an egg can result in a chalky or crumbly texture in the yolk. This occurs when the yolk proteins are over-coagulated, resulting in a denser and more brittle structure.

The boiling time of an egg will determine the extent of these changes. A soft-boiled egg will have a runny or semi-liquid yolk, while a hard-boiled egg will have a completely solidified yolk. The amount of time needed for boiling also depends on factors like the size of the egg and the desired level of doneness.