Recipes use whole eggs for mayonnaise when a lighter, less rich flavor and texture are desired, while using only yolks results in a richer, creamier, and more stable emulsion due to the higher fat content.
The key to mayonnaise is emulsification – the process of combining oil and water-based liquids (like lemon juice or vinegar) into a stable mixture. Egg yolks contain lecithin, a natural emulsifier that helps bind these liquids together.
When a recipe calls for whole eggs, it's incorporating both the yolk and the white. The yolk provides the emulsifying power, while the egg white adds liquid and protein. This results in a mayonnaise that is generally lighter in color, flavor, and texture. The presence of the egg white dilutes the richness of the yolk, creating a less intense flavor profile.
On the other hand, recipes using only egg yolks create a much richer and more decadent mayonnaise. The higher concentration of lecithin and fat in the yolks leads to a thicker, creamier texture and a more pronounced eggy flavor. This type of mayonnaise is also often more stable, meaning it's less likely to separate. The increased fat content contributes to a more robust emulsion that can withstand slight variations in temperature or handling.
Always use pasteurized eggs or yolks when making mayonnaise, especially if serving to pregnant women, young children, or individuals with compromised immune systems, to minimize the risk of salmonella.