What ingredient is commonly used as a thickener in sauces?

Cornstarch or flour is a common ingredient used as a thickener in sauces due to their ability to absorb liquids and swell, creating a thicker consistency. When cornstarch is mixed with a cold liquid and then added to hot liquids, it gelatinizes and helps to thicken sauces efficiently. Flour, when cooked properly, also helps to achieve a thickened texture. This process is essential in culinary practices for creating velvety sauces, gravies, or soups, ensuring they have the desired mouthfeel and viscosity.

In contrast, sugar is mainly used for sweetness and does not contribute to thickening. Butter, while it adds richness and flavor, does not effectively thicken sauces on its own. Baking soda serves a different purpose, typically as a leavening agent in baked goods, and is not utilized for thickening sauces.