View source for Primary fermentation

'''Primary fermentation''' is the initial and principal stage of [[fermentation]] in [[winemaking]], during which sugars present in grape must are converted into [[ethanol]], [[carbon dioxide]], and a range of [[secondary metabolites]] by [[yeast]] activity<ref>Jackson, ''Wine Science: Principles and Applications'', 5th ed., 2020.</ref>. It is also known as alcoholic fermentation and forms the basis of virtually all [[wine]] styles before further processes such as [[secondary fermentation]] or maturation occur.

== Definition and Context ==
Primary fermentation refers specifically to the transformation of grape sugars, chiefly glucose and fructose, into alcohol and carbon dioxide under anaerobic conditions<ref>Robinson (ed.), ''The Oxford Companion to Wine'', 2015.</ref>. This stage is distinguished from secondary processes such as malolactic fermentation, in which lactic acid bacteria convert malic acid into lactic acid.  

== Microbiology and Process ==
The conversion is driven primarily by strains of ''Saccharomyces cerevisiae'', although other yeast species may be involved, especially in spontaneous fermentations<ref>Boulton, Singleton, Bisson & Kunkee, ''Principles and Practices of Winemaking'', 1999.</ref>. Under controlled cellar conditions, [[fermentation]] usually lasts between one and three weeks, depending on [[temperature (wine)|temperature]], [[must composition]], and [[yeast health]]. Temperature is a critical factor: cooler fermentations are often used for [[white wines]] to preserve delicate [[aromas]], whereas warmer fermentations are common for [[red wine|reds]] to enhance extraction of [[colour]] and [[tannins]]. [[Oxygen management]], nutrient availability, and must pH also play important roles in determining fermentation kinetics and stability<ref>AWRI, “Fermentation management”, awri.com.au.</ref>.

== Influence on Wine Style ==
Primary fermentation shapes the [[aromatic profile]], [[flavour]], and [[texture]] of the finished wine. The process determines the final [[alcohol]] concentration, while also producing esters, higher alcohols, and volatile acids that contribute to aroma complexity<ref>Jackson, ''Wine Science: Principles and Applications'', 5th ed., 2020.</ref>. In red wines, fermentation often occurs on skins, facilitating extraction of [[anthocyanins]] and tannins. In white winemaking, by contrast, fermentation typically takes place without skin contact, yielding fresher, [[lighter-bodied]] wines.

== Fermentation Management ==
Winemakers may manage fermentation by selecting cultured yeast strains or allowing indigenous populations to dominate. Vessel choice significantly affects outcomes: stainless steel tanks enable precise temperature control, while oak vats or [[barrels]] can contribute [[micro-oxygenation]] and additional flavour compounds<ref>Boulton, Singleton, Bisson & Kunkee, ''Principles and Practices of Winemaking'', 1999.</ref>. Stuck or sluggish fermentations present challenges that may require intervention through [[aeration]], nutrient addition, or re-inoculation with vigorous yeast.

== See also ==
* [[Fermentation]]  
* [[Secondary fermentation]]  
* [[Yeast]]  
* [[Winemaking techniques]]  

== References ==
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[[Category:Viticulture]]
[[Category:Winemaking]]