Final answer:
Beurre blanc is not made with egg yolks; it is an emulsion of butter in vinegar and/or white wine. Egg yolks contain lecithins, which are emulsifiers in mayonnaise and hollandaise, not in beurre blanc. Casein in milk is another example of an emulsifying agent, creating an emulsion of butterfat in water.
Step-by-step explanation:
Beurre blanc, contrary to the question's claim, is not emulsified with egg yolks. Instead, this classic French sauce is an emulsion of butter into a reduction of vinegar and/or white wine, typically seasoned with shallots, salt, and herbs. The stable emulsion in beurre blanc is achieved through the gradual incorporation of cold, diced butter into the acidic reduction while whisking at a lower temperature, which allows the butter's fat to become suspended in the acidic liquid without separating.
Egg yolks, however, play a central role in the emulsification of sauces like mayonnaise or hollandaise. In these cases, the egg yolks contain lecithins, which are emulsifying agents that help stabilize the mixture. Lecithins interact with both polar (water-based) and nonpolar (oil-based) substances to create a stable emulsion. By contrast, the protein casein in milk acts as an emulsifying agent by keeping the butterfat suspended in water, creating another well-known emulsion.