What ingredient is often added to a sauce to enhance flavor and acidity?

Vinegar is commonly used in sauces to enhance both flavor and acidity. The addition of vinegar can brighten the overall taste of a sauce, providing a sharp contrast that balances richness or sweetness. Its acidic properties can help to cut through fatty components, making the dish feel lighter and more vibrant. Different types of vinegar, such as balsamic, red wine, or apple cider, can impart unique flavors, adding depth to the sauce.

While sugar can add sweetness, it does not contribute acidity. Salt is primarily used to enhance flavor but does not affect acidity directly. Butter adds richness and a creamy texture but lacks the tanginess characteristic of an acidic ingredient. Hence, vinegar stands out as the ideal choice for enhancing both flavor and acidity in sauces.