Sherry production is concentrated in the Sherry Triangle, the region defined by the cities of Jerez, Sanlúcar and El Puerto de Santa Maria. Grapes, production methods and soils are relatively similar; temperature and climate distinguish the cities. Hot, inland Jerez produces Sherries with deep colors and full, nutty flavors. Sanlúcar, by contrast, is closer to the Atlantic and cooler, and its Sherries are pale and sharply acidic [source: Cellar Tours].
In Andalucia, the soil -- called albariza by locals -- has a great deal of limestone. It's a white, porous mix of chalk, limestone, sand and clay [source: Shea]. Because it's so porous, it can absorb and hold water well; that's important in a region as dry and sunny as Andalucia.
Sherries start with white Palomino Fino grapes. Additional varietals, if used at all, may include Muscatel and Pedro Ximénez. Grapes are left on the vines until they're slightly overripe, with a higher sugar content [source: Good Cooking]. Then they're harvested, usually near the beginning of September, and pressed almost immediately. Only then do producers divide the press into the clean, aromatic finos and manzanillas, and the heavier-bodied wines destined to become olorosos [source: Cellar Tours].
In fact, more than other wines, Sherry is defined by its aging process. Arguably, maturation has a greater effect than terroir on the final product. Most other wine matures in airtight containers, but sherry ages in the open air. It develops a surface coating of yeast, or "flor," which acts as a seal against the air [sources: Shea, Cellar Tours]. The flor grows and ebbs seasonally.
Sherry ages for at least five years. Over that time, producers use a traditional method of aging and blending called solera, which is something like a cross between a sourdough starter and a very slow champagne waterfall.
In solera aging, the casks are stacked in a vertical arrangement called a criadera (variously translated as "nursery" or "hotbed"). The solera is the bottom level of the criadera. The newest wine is always at the top. The casks are never filled all the way; the extra space allows for the development of the flor [source: Cellar Tours].
Every year, some of the bottom sherry is removed and bottled. It's replaced with sherry from the cask above. And so on and so on. Some soleras have been in continuous operation since the 19th century; fine reserve Sherries may indeed contain elements that old [sources: Shea, Cellar Tours].
On the next page, we'll take a look at the Spanish wines that result from the bloom of the flor.