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'''Secondary fermentation''' refers to a subsequent stage of [[fermentation]] that follows the initial alcoholic fermentation in winemaking. It plays a crucial role in both [[sparkling wine|sparkling]] and [[still wines]], influencing [[texture]], [[flavour]], stability, and overall style.<ref>Robinson (ed.), ''The Oxford Companion to Wine'', Oxford University Press, 2015.</ref>  

== Background ==  
In primary fermentation, yeasts convert grape sugars into [[alcohol]] and [[carbon dioxide]], creating the base wine. Secondary fermentation encompasses several processes, most notably the bottle or tank fermentation used in the production of sparkling wines, and [[malolactic fermentation]] in many still wines.<ref>Boulton, Singleton, Bisson & Kunkee, ''Principles and Practices of Winemaking'', Springer, 1999.</ref> These steps have been refined over centuries, particularly in regions such as [[Champagne]], where secondary fermentation underpins the [[traditional method]] of sparkling wine production.<ref>Stevenson, ''Christie’s World Encyclopedia of Champagne and Sparkling Wine'', Absolute Press, 2013.</ref>  

== Characteristics ==  
From a microbiological standpoint, secondary fermentation may involve either [[yeast]] or [[lactic acid bacteria]]. In sparkling wines, an additional dose of [[sugar]] and yeast is added to the [[base wine]], which ferments in a sealed environment and generates carbon dioxide, creating [[effervescence]]. This process can occur in individual bottles (traditional method) or in large pressurised tanks ([[Charmat method]]).<ref>Jackson, ''Wine Science: Principles and Applications'', Academic Press, 2020.</ref>  

In still wines, secondary fermentation often refers to malolactic fermentation ([[MLF]]). This bacterial conversion transforms sharper [[malic acid]] into softer lactic acid, reducing [[acidity]] and adding [[complexity]] to the [[flavour]] and [[mouthfeel]. MLF is common in [[red wines]] and some [[whites]], particularly [[Chardonnay]].<ref>Robinson (ed.), ''The Oxford Companion to Wine'', Oxford University Press, 2015.</ref>  

== Use in winemaking ==  
The use of secondary fermentation varies according to style and region:  
* In sparkling wines such as [[Champagne]], [[Cava]], and some [[Prosecco]], the secondary fermentation is essential for the formation of bubbles. Bottle-fermented wines generally gain additional complexity through [[lees]] ageing.  
* In still wines, MLF provides microbiological stability and contributes [[buttery (note)|buttery]], [[nutty (note)|nutty]], or [[creamy (note)|creamy]] notes. Winemakers may encourage, inhibit, or partially apply this process depending on the desired style.  
* Some [[fortified wines]] and speciality styles also involve secondary fermentations, though these are less common and highly specific to regional traditions.  

== See also ==  
* [[Fermentation]]  
* [[Champagne]]  
* [[Malolactic fermentation]]  

== References ==  
{{reflist}}  

[[Category:Winemaking]]  
[[Category:Wine chemistry]]