Name a key ingredient in a traditional Caipirinha cocktail.

The key ingredient in a traditional Caipirinha cocktail is cachaça. Cachaça is a Brazilian spirit made from fermented sugarcane juice and is the defining element of this classic cocktail. The Caipirinha combines cachaça with fresh lime and sugar, often served over ice, creating a refreshing drink that highlights the unique flavors of cachaça.

The other spirits listed do not belong to the traditional recipe. Tequila is a Mexican spirit made from the agave plant, vodka is a neutral spirit typically made from grains or potatoes, and rum is derived from sugarcane or molasses but does not have a place in a Caipirinha. The presence of cachaça specifically is what authenticates the cocktail as a Caipirinha, differentiating it from drinks that might use other spirits.