What is often a key component in determining the richness of hollandaise sauce?

In determining the richness of hollandaise sauce, butter plays a pivotal role. Hollandaise sauce is an emulsified sauce made primarily from egg yolks, butter, and an acid, such as lemon juice. The use of butter not only contributes to the sauce's texture but also enhances its flavor profile, providing a creamy and decadent quality that is characteristic of hollandaise.

While lemon juice adds brightness and acidity, which are important for balancing the sauce, it is the butter that contributes the primary richness. The emulsification of the butter with the egg yolks creates a luxurious mouthfeel, making the sauce velvety and indulgent.

Egg whites are generally not used in hollandaise, as they can create a lighter texture that is not desired in this particular sauce, and mustard, while it can sometimes be added for flavor, does not impact the richness in the same way butter does. Thus, it is the incorporation of butter that defines the sauce's sumptuousness.