What is a key effect of acidity in coffee?

The key effect of acidity in coffee is brightness and complexity. Acidity contributes to the overall balance of flavors in a cup of coffee, enhancing its vividness and creating a more dynamic tasting experience. When coffee has a noticeable acidity, it can evoke a sense of liveliness on the palate, making the flavors stand out and interact more intriguingly. This brightness can be perceived in various forms depending on the coffee's origin and processing method, from fruity and tart notes to floral and citrus undertones, which enrich the complexity of the beverage.

The other options suggest attributes that do not correlate with acidity. For instance, bitterness is often more closely related to the coffee bean's roasting level rather than its acidity. An overly sweet flavor can sometimes mask acidity, and oiliness is associated with the coffee's brewing method and the type of beans used, not acidity itself. Thus, the sense of brightness and complexity distinctly reflects the role of acidity in enhancing the coffee profile.