What key ingredient would you expect in a horseradish sauce?

The key ingredient in horseradish sauce is the horseradish root itself. Horseradish is a pungent root that is grated and mixed with vinegar and other ingredients to create the distinctive flavor of the sauce. It is known for its sharp, spicy kick and is often used as a condiment for meats, seafood, and sandwiches. The primary purpose of horseradish in the sauce is to provide that characteristic heat and aroma that enthusiasts look for.

While carrots, beets, and onions might add flavors to various sauces or condiments, they do not play a role in horseradish sauce; their inclusion would significantly change the nature and taste of the sauce. Therefore, the presence of horseradish root makes it the essential ingredient in this particular preparation.