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Fermentation is a metabolic process that converts sugar to acids, gases, or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. Fermentation is also used more broadly to refer to the bulk growth of microorganisms on a growth medium, often with the goal of producing a specific chemical product. French microbiologist Louis Pasteur is often remembered for his insights into fermentation and its microbial causes. The science of fermentation is known as zymology.
Choice of bottle shapes is traditional — or whimsical — depending on the winemaker. For example Cabernets are normally bottled in square-shouldered Bordeaux bottles, while Chardonnays are in slope-shouldered Burgundies. For the less fussy or larger-scale producer, these niceties can give way to using whatever bottles are at hand. Clear glass bottles are not recommended unless you can be sure the wine will not come into contact with direct sunlight, which can brown the bottle’s contents. Figure on 25 750-milliliter bottles for a five-gallon carboy of wine. This often allows a little extra, which can be a needed libation for the winemaker.
An appellation is a legally defined and protected geographical indication used to identify where the grapes for a wine were grown; other types of food often have appellations as well. Restrictions other than geographical boundaries, such as what grapes may be grown, maximum grape yields, alcohol level, and other quality factors, may also apply before an appellation name may legally appear on a wine bottle label. The rules that govern appellations are dependent on the country in which the wine was produced.
The aging of wine (American English) or ageing of wine is potentially able to improve the quality of wine. This distinguishes wine from most other consumable goods. While wine is perishable and capable of deteriorating, complex chemical reactions involving a wine's sugars, acids and phenolic compounds (such as tannins) can alter the aroma, color, mouthfeel and taste of the wine in a way that may be more pleasing to the taster. The ability of a wine to age is influenced by many factors including grape variety, vintage, viticultural practices, wine region and winemaking style. The condition that the wine is kept in after bottling can also influence how well a wine ages and may require significant time and financial investment.