What key ingredient is often added to a sauce to artificially thicken it?

The key ingredient commonly added to a sauce to artificially thicken it is flour. When flour is mixed with a liquid, it creates a slurry, which, when heated, thickens the sauce through a process called gelatinization. The starches in the flour absorb liquid and swell, adding body and viscosity to the sauce. This technique is widely used in various culinary traditions to achieve a desirable texture and consistency in sauces, gravies, and soups.

In comparison, while butter can enhance flavor and richness, it does not have significant thickening properties on its own. Rice, unless pureed or used as a starch, typically serves more as a grain component rather than a thickening agent. Vegetables might add texture or flavor but are usually not ground into the sauce in the same manner as flour for thickening purposes.