What happens when egg yolk is beaten at a high speed?

Beating egg yolk at a high speed causes denaturation and emulsification. Here's what happens:

1. Denaturation: The proteins in the egg yolk, particularly the lipoproteins, start to unfold and lose their original structure when subjected to high-speed beating or whipping. This process is known as denaturation.

2. Emulsification: The denatured egg yolk proteins have the ability to form and stabilize an emulsion, which is a mixture of two immiscible liquids (in this case, oil and water). The egg yolk proteins act as emulsifiers, allowing oil and water to coexist stably in a uniform mixture.

3. Formation of Foam: As air is incorporated during the beating process, the denatured egg proteins trap and stabilize the air bubbles, leading to the formation of foam. The trapped air expands, causing the mixture to increase in volume and become lighter and fluffier.

4. Creaming: The combination of denaturation and air incorporation results in the creaming of the egg yolk. The mixture becomes thick, creamy, and pale yellow in color due to the dispersion of light by the tiny air bubbles.

The creaming property of beaten egg yolk is crucial in various culinary preparations, such as mayonnaise, salad dressings, sauces, mousses, and cakes. It provides richness, structure, and stability to these foods.