Which of the following is a common thickening agent used in sauces?

Cornstarch is indeed a common thickening agent used in sauces due to its unique properties. When mixed with a cold liquid and then heated, cornstarch gelatinizes, which thickens the sauce effectively without adding much flavor. This characteristic makes it an ideal choice for bringing body and texture to a wide variety of sauces while allowing the main flavors to shine through.

Its effectiveness as a thickener is particularly valuable in applications like gravies, stir-fries, and fruit sauces, where a clear and glossy finish is often desired. The ability of cornstarch to create a smooth texture also means it helps prevent lumps in the sauce, which can be an issue with other thickening agents if not properly handled.

Flour, another common thickening agent, is typically used in a roux or as a slurry, but it can impart a distinct taste and may not create the same transparent effect as cornstarch. Butter primarily serves as a fat for richness and mouthfeel rather than a thickener, and sugar has a different role, mainly for sweetness rather than adding body to sauces.