The sherry cask, or ‘bota’, holds 516 litres and is made out of American oak, which allows the wine to ‘breathe’ through its pores. Casks are never filled to the brim, and the top is never fully sealed. The air chamber that remains in the cask and the air that seeps in through the stopper are essential in guaranteeing a degree of oxidation, which is the key to making sherry wine.

In the case of finos, this ageing process painstakingly supervised by the winemaker is completed with a second biological process. This happens on the surface of the wine, by virtue of a head of yeast called the ‘flower’ or ‘veil’. This head avoids oxidation, by sealing the wine off from the air.

Oloroso wines do not develop the yeast head, but undergo an ageing process based on slow oxidation and extraction from the oak. Amontillado wines have a bit of both, with an early ageing as finos and a second stage as olorosos. Finos that have undergone a long ageing process are also called "amontillados finos".

In the cellar, casks contain wine of all ages, with the ones closest to the ground (the “soleras”) containing older wine, and the ones above (“criaderas”) filled with younger wine. Each of the basic types of sherry wine is taken to a specific solera, since each cellar has casks for finos, amontillados and olorosos.

Both scent and sight are essential when it comes to classifying sherry wines. The taster makes chalk marking on each cask to indicate how the wine is developing. If it is pale, with a fresh fruity bouquet, it is moving towards a fino, or perhaps an amontillado. If is bolder and less pale, then it is pointing towards an oloroso.