Named after the Montilla region where this style of wine originated in the 18th century, an amontillado sherry begins as a fino, fortified to approximately 13.5 percent alcohol with a cap of flor yeast limiting its exposure to the air. A cask of fino will be reclassified as amontillado if the layer of flor fails to develop adequately or is intentionally killed by non-replenishment or additional fortification. Without the layer of flor, amontillado must be fortified to approximately 17.5 alcohol so that it does not oxidize too quickly. After the additional fortification, amontillado oxidizes slowly, exposed to oxygen through the slightly porous American or Canadian oak casks, and gains a darker color and richer flavor than fino.
The Amontillado name is sometimes used commercially as a simple measure of color to label any sherry lying between a fino and an oloroso.
Due to its oxidative aging and preparation, amontillado is more stable than fino and may be stored for a few years before opening. After opening, it can be kept, corked and refrigerated, for up to two weeks.