I am trying to understand how emulsions work and I am confused by why certain ingredients are used in certain recipes.
Beurre Blanc: Traditionally a Beurre Blanc is made with white wine and butter. However, modern chef's often stabilize the sauce by adding a splash of heavy cream. What is the emulsifying agent in butter? I see references to milk proteins. Is this lecithin? Is the same emulsifying agent in heavy cream in higher concentrations or is it something different?
Mayonnaise: Mayonnaise contains egg yoke, oil, and lemon juice. The emulsifier in this case is lecithin from the egg yoke. I notice many emulsifications have an acid component. Does acid have a role in emulsification other than as a preservative or flavoring component?