What characteristic distinguishes an Amontillado from a Fino?

Amontillado is distinguished from Fino primarily by the presence of oxidative aging. While both are styles of Sherry, Fino is aged under a layer of flor yeast, which protects the wine from oxygen and gives it a lighter, fresher profile. In contrast, Amontillado begins its aging process similarly under flor but subsequently undergoes a second phase of oxidative aging without the flor. This exposure to oxygen deepens the wine's color, enhances its complexity, and contributes to its nutty, richer flavor profile.

The oxidative aging that characterizes Amontillado creates a distinctive taste and aroma that differs significantly from the clean and bright characteristics typically found in Fino. The transition from biological aging to oxidative aging is crucial to understanding the stylistic differences between these two types of Sherry.