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Natural Yeasts: These are yeasts that occur naturally on the grapes, rather than commercially cultured yeasts; both are used for fermentation. Many feel that the natural yeasts add more complexity to the wine. Large-scale producers shy away from natural yeasts, which can be unreliable since they are less controlled than cultured varieties.
Yeast: Micro-organisms that convert sugar to alcohol and carbon dioxide in the process known as fermentation. The predominant wine yeast, saccharomyces cerevisiae, is the same micro-organism that ferments beer and makes bread dough rise. Three categories of yeasts are common, including cultured, natural and wild.
Alcohol: Ethyl alcohol, a chemical compound formed by the action of natural or added yeast on the sugar content of grapes during fermentation.
Carbonic Maceration: Most frequently associated with Beaujolais, this is a method of producing light-bodied, fresh and fruity red wines. Instead of crushing the grapes and releasing the juices to be fermented by yeasts, whole grape bunches are placed in a tank and the oxygen is displaced by carbon dioxide. Fermentation starts on an intracellular level inside the berry, producing some alcohol as well as fruity aromatics. In practice, the weight of the grapes on the top crushes the grapes on the bottom and yeasts ferment the juice; the wine is partly a product of carbonic maceration and partly of traditional yeast fermentation.
Cloudiness: Lack of clarity to the eye. Fine for old wines with sediment, but it can be a warning signal of protein instability, yeast spoilage or re-fermentation in the bottle in younger wines. Cloudiness may also represent a deliberate choice by the winemaker not to filter a wine.
Lees: Sediment—dead yeast cells, grapeseeds, stems, pulp and tartrates (harmless tartaric acid crystals)—remaining in a barrel or tank during and after fermentation. "Sur lie" is a French term for aging a wine on its lees.
Sur Lie: Wines aged sur lie (French for "on the lees") are kept in contact with the dead yeast cells and are not racked or otherwise filtered. This is mainly done for whites, to enrich them. (It is a normal part of fermenting red wine, and so is not noted.) The concept originated in Burgundy, with Chardonnay, but is now popular around the world with numerous white grape varieties. Sur lie aging can be overdone, leading to an off-putting leesy flavor.
Brettanomyces (Brett): A spoilage yeast that can cause what are commonly described as barnyard aromas and flavors in a wine. Some people feel that, in small amounts, it can add a pleasant spicy, leathery component or complexity to a wine. Others feel that it is a flaw in any amount. Sensory thresholds and tolerance of brett vary.
Alcoholic Fermentation: Also called primary fermentation, this is the process in which yeasts metabolize grape sugars and produce alcohol, carbon dioxide and heat. The final product is wine.
Organic Wine: The rules and methods for producing organic grapes and wine are still evolving. The answer usually depends on the country of origin and the various governing organizations involved. France, for example, legally defined organic farming in 1981 as "farming which uses no synthetic chemical products." In most cases, organic wines are fermented from grapes grown without the use of synthesized fertilizers, pesticides or herbicides. In organic wines, natural yeasts and minimal amounts of sulfur are often used in the fermentation process.
Secondary Fermentation: The process that creates the bubbles in sparkling wine. As the wine is bottled, a small amount of yeast and sugar is added before the bottle is sealed with a sturdy crown cap. The yeasts quickly start fermenting the sugars, producing alcohol and carbon dioxide. Since the gas cannot escape, it dissolves into the wine.
Temperature of Fermentation: As yeasts convert grape sugars into alcohol, they also produce heat. Excessively high temperatures can kill the yeasts and make the wine’s fruit flavors seem stewed or dull, whereas cooler temperatures maintain the freshness of the fruit. Just the right amount of warmth can contribute a richer, rounder mouthfeel.
Microoxygenation: This technique, used almost exclusively on red wines, allows winemakers to control the amount of oxygen that wines in tank are exposed to. The apparatus involves chambers connected by tubes and valves to an oxygen tank. Small, measured amounts of oxygen are allowed to pass through the wine via a porous stone or ceramic plate at or near the base of the tank. The benefits of this type of oxygen exposure include prevention of oxidation and reduction as well as promotion of healthy yeast cultures, which prevent stuck fermentations. Microoxygenation is also believed to soften tannins and, in conjunction with the use of oak chips, is frequently practiced as an alternative to oak barrel aging.
Winemaking: Largely synonymous with "Vinification," winemaking is the process by which harvested grapes are crushed, fermented (and otherwise manipulated through yeast inoculations, temperature control, punch-downs, pump-overs, racking, oak-chip additions, filtering, etc.), aged in barrel, steel tank or other vessel, and finally bottled.
Fino: Fino is the driest classification of Sherry wines. The freshest and palest category of Sherry, finos are protected from oxygenation by a cap of flor yeast while aging in barrel.
Oloroso: Oloroso is the darkest, richest category of dry Sherry. The wines are aged oxidatively, without the flor yeast cap that protects finos and amontillados, and may have alcohol levels up to 20 percent. The wines have a nutty aroma and flavor, and serve as the base for cream Sherry dessert wines.
Amontillado: Amontillado is a category of Sherry which begins aging in the same manner as a fino Sherry, with a flor yeast cap to protect from oxidation and keep the wine fresh-tasting, but amontillado is then exposed to oxygen, allowing the wine to darken, becoming richer than a fino but still lighter than an oloroso.
Flor: Flor is the Spanish term for a cap of yeast that forms over Sherry wine as it ages in barrel, protecting the wine from oxidation.
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