Amontillado is a variety of sherry wine characterized by being darker than fino but lighter than oloroso. It is named after the Montilla region of Spain, where the style originated in the eighteenth century, although the name 'Amontillado' is sometimes used commercially as a simple measure of colour to label any sherry lying between a fino and an oloroso. 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 is considered to be amontillado if the layer of flor fails to develop adequately, is intentionally killed by additional fortification or is allowed to die off through non-replenishment. Without the layer of flor, amontillado must be fortified to approximately 17.5 percent alcohol so that it does not oxidise too quickly. After the additional fortification, amontillado oxidises slowly, exposed to oxygen through the slightly porous American or Canadian oak casks, and gains a darker colour and richer flavour than fino.