Acidification: the practice of artificially increasing the acidity of grape must by the addition of tartaric, citric or malic acids. It is most prevalent in warm wine regions where the grapes' natural acids (mainly malic acid) tend to degrade during ripening.
Acidity: the measure of organic acids (most obviously tartaric, malic and citric) in a wine. Acidity plays a vital role in winemaking. Acids act as a natural antiseptic and preservative, avoiding bacterial spoilage and giving wine the structure it needs for ageing. They also define how the wine feels in the mouth; a wine with balanced acidity is both better structured and more refreshing. The natural acidity of grape berries varies between varieties, from high-acid (e.g. Ugni Blanc) to low-acid (e.g. Dolcetto).
Alluvial: a fertile soil type composed of fine-grained elements such as clay, sand, silt and sometimes gravels or stones. Alluvial soils are created when these sediments are deposited by flowing water.
Altitude: the height above sea level of a particular geographical location. Altitude can have a strong influence on wine style. Higher vineyard locations are typically cooler (air temperature drops about 1.1F/0.6C with every 330ft/100m of altitude), which makes for a longer, slower growing season with greater hang time. By contrast, some locations are simply too high (and therefore too cool) for grapes to ripen properly.
Amontillado: an amber-colored Sherry style half-way between the Fino and Oloroso styles. Amontillado begins life as Fino, but as the flor yeast dissipates the wine is exposed to oxygen and begins to develop rich, nutty flavors like those found in Oloroso.
Anthocyanins: naturally occurring phenolic compounds responsible for the red/purple color of red-wine grapes and many other fruits and vegetables.
Appellation: the official title given to a product made in a specific place (or set of places), in a style particular to that place. France is home to the world's most famous appellation system, a model which has been adopted as a model for Europe-wide regulations (see European Wine Labels). Most appellations take the form of place names (e.g. Champagne, Barolo, Jerez-Xerez-Sherry). Over time the word has developed a secondary, simpler usage, indicating only a place (e.g. Napa Valley) rather than a product.
Aspect: a geographical term indicating the direction in which a slope faces. This is a key component of terroir; a vineyard site's aspect determines the timing and intensity of the sunshine it receives. The finest sites in Burgundy, for example, are those with a south-easterly aspect which exposes them to gentle morning sunshine but avoids the harsher heat of the afternoon. Aspect is particularly important in cooler regions, where grapes struggle to ripen on anything but the sunniest slopes.
Barrel fermentation: a winemaking technique in which grape must is fermented in barrels in order to integrate the flavors of the wood (almost always oak) into the wine (usually Chardonnay). Wines both fermented and matured in barrel typically have better-integrated oak flavors than those only matured in barrel.
Barrel maturation: the maturation of wine in barrels (usually oak) after fermentation. The process softens tannins, stabilizes color and (particularly when new oak barrels are used) imparts oaky, vanilla-like flavors into the wine.
Battonage: the act of stirring wine in a tank, vat or barrel, in order to agitate the lees. This increases interaction between wine and lees, ultimately making the wine more complex in both flavor and mouthfeel. Traditionally done with a wooden baton, whence the name.
Bereich: a German administrative area. Each of Germany's 13 Anbaugebeite (official wine-producing regions) is divided into smaller districts, the Bereiche (e.g. Bereich Bernkastel). Although these are rarely mentioned on labels, they still exist as part German's wine and land administration.
Botrytis: the common name for the fungus Botrytis cinerea. In its benevolent form ('noble rot'), this fungus is vital to the production of certain sweet/dessert wines (most famously Sauternes and Tokaji). The spores develop in environments where moist air and dry air alternate, allowing the fungus to develop, but not to evolve into its destructive form 'grey rot' (which destroys the berry and causes sour, vinegary flavors in wine). Grape berries affected by botrytis gradually dry out on the vine, naturally concentrating their sugars and flavor compounds.
Brettanomyces: (often abbreviated to 'brett') is a spoilage yeast associated with mousey, farmyard-like aromas in wine. It is not brett itself which causes these unpleasant aromas, but rather the phenols it produces: 4-ethylphenol (4EP) and 4-ethylguiacol (4EG). The brettanomyces yeast is very sensitive to sulfur dioxide and can be inhibited with a judicious dose of SO2 as well as maintaining cool cellar temperatures.