Barrel Fermentation (Chardonnay, Sémillon, Whites)

Barrel fermentation means carrying out the alcoholic fermentation of white wine in oak casks rather than in vessels such as stainless steel vats or concrete tanks. Many of the world's greatest white wines ferment and mature in oak casks, and the work is labour intensive. Californian Chardonnay is renowned for making full use of malolactic fermentation, lees contact, and oak barrel fermentation and maturation. In Bordeaux, the Semillon and Sauvignon Blanc dry whites of Pessac-Léognan are often barrel-fermented.

• Domaine Leflaive's Puligny-Montrachet goes through alcoholic and malolactic fermentation in oak casks.
• Malolactic fermentation is a separate, bacterial process: Oenococcus oeni is the main bacterium responsible, and inoculation most commonly follows alcoholic fermentation.
• A wine matured in oak takes on flavours from the toasted wood, such as vanilla, toasted bread and spice, and oak ageing can also add body.
• The technique is not limited to Chardonnay and Semillon: some Margaret River Chenin Blanc is wild-fermented in oak barrels, while other examples are fermented in stainless steel.

Domaine Leflaive decants over 24 hours, then racks and runs the juice into barrels, while Vasse Felix ferments unclarified juice with only wild yeast. During the active fermentation phase, yeasts transform sugar into alcohol in intimate contact with the wine, then die and sink to the bottom of the barrel to form a layer of lees. Oxygen enters through the barrel staves and the bunghole, and the lees can scavenge it, especially when they are stirred. Some winemakers leave the wine on its fine lees, which can enrich its mouthfeel as dead yeast cells autolyse and release mannoproteins, and whose nutrients can support malolactic fermentation.

• Post-fermentation lees contact in barrel is a traditional method in many parts of Europe, most commonly associated with Burgundian Chardonnay, and the lees scavenge oxygen, protecting the wine through fermentation and maturation; at Domaine des Comtes Lafon, bâtonnage (lees stirring) was used sparingly.
• A small amount of stirring at the end of fermentation is recommended, because stirring encourages continued yeast cell viability, which encourages the assimilation of any residual sugar.
• Excessive stirring can introduce too much oxygen, leading to the loss of SO2 and potentially acetaldehyde and acetic acid; in a Brajkovich (2008) trial, the barrel-fermented Chardonnay that was neither stirred nor topped was preferred after four months.
• More heavily toasted barrels lend a wine sweetness and amplitude and roasted aromas of coffee and caramel, while lighter toast levels bring aromas of vanilla and fresh wood to the fore.

As yeast cells in the lees break down, a process known as autolysis, they release amino acids and polysaccharides that improve flavour and texture, as well as glutathione, an important antioxidant. Benefits attributed to lees contact include increased texture, greater oak, fruit and yeast integration, more complexity, and improved oak aromas and flavours. Chardonnay made with extensive oak contact, malolactic fermentation and lees contact becomes a toasty, buttery, creamy wine, while winemakers who block malolactic fermentation and eschew oak for stainless steel get a purer expression of the variety's characteristics. Jean-François Coche-Dury believes intimate contact between wine and lees is critical to quality: "The wines acquire strength and structure, muscles and sinew".

• One of the major compounds produced by Oenococcus oeni during malolactic fermentation is diacetyl, which contributes buttery or butterscotch aroma, and butteriness can be masked by strong oak or very fruity characters.
• Among malolactic winemaking techniques, long yeast lees contact is linked to a lower diacetyl concentration.
• Lees contribute to a buttery mouthfeel, increased complexity and aromas like brioche and toasted nuts, and mannoproteins reduce tartrate precipitation and promote protein stability.
• In Bordeaux blends with Sauvignon, Semillon can be citrusy with a lanoline-textured, waxy, honeyed richness.

Within one estate the choice can vary: Domaine Leflaive ferments its Puligny-Montrachet, Bâtard-Montrachet and Chevalier-Montrachet in oak casks, but its Pouilly-Fuissé in a variable combination of stainless steel vats, foudres, concrete tanks and 600L barrels. In Margaret River, Chardonnay complexity is often expressed through natural fermentation in French oak barrels, while the Sauvignon Blanc and Semillon blend is often fermented in stainless steel and enjoyed fresh. Inexpensive to mid-priced Central Valley Chardonnay in California is likely to get any oak influence from oak chips or staves, and the trend in the United States has been toward more balanced styles with moderate or no oak use.

• White Burgundy: Domaine Leflaive in Puligny-Montrachet ferments in oak casks, and the white wines at Domaine des Comtes Lafon in Meursault, like the reds, were fermented with natural yeasts.
• Sauternes: the 2020 Château d'Yquem spent 22 months in 100% new oak, something that is "key" for the estate.
• Margaret River Semillon and Sauvignon Blanc: practices such as grape skin-contact and oak during fermentation, and fermentation vessels such as foudres, are driving complexity and ageability in a new generation of styles.
• Stainless steel instead: some winemakers choose to block malolactic fermentation and eschew oak for stainless steel, resulting in a purer expression of Chardonnay's varietal characteristics.

Domaine Leflaive in Puligny-Montrachet gives its Puligny-Montrachet, Bâtard-Montrachet and Chevalier-Montrachet a long, gentle pneumatic pressing, decants over 24 hours, then racks the juice into barrels for alcoholic and malolactic fermentation in oak casks, followed by 12 months in barrels on lees and 10 months in stainless steel tank on fine lees. At Domaine des Comtes Lafon in Meursault, Montrachet was the only wine aged entirely in new oak and the premiers crus were aged in a proportion that varied from 25% to 40% and stayed in wood for 16 months. In Sauternes, Château d'Yquem's 2023 is 70% Sémillon and 30% Sauvignon Blanc; ageing was reduced from at least 36 months in new oak under Lur-Saluces to no more than 30 months, and the 2020 vintage spent 22 months in 100% new oak. In Margaret River, Pierro's 2020 VR Reserve Chardonnay was whole bunch pressed, fermented in French oak barriques using a mix of natural and cultured yeasts, taken through a full malolactic fermentation and given 12 months in 100% new French oak with regular bâtonnage.

• Domaine des Comtes Lafon: Dominique Lafon used lees-stirring "usually when the fermentation is slow to finish or when the wine is reduced", and his cellars are notoriously cold, so fermentations can be slow.
• Château d'Yquem: in the words of estate manager Lorenzo Pasquini in 2023, "In the last 15 years, spontaneous yeasts mean a longer, slower fermentation with no racking, cooling or adding sulphur."
• Vasse Felix: Chardonnay picked early in the morning, chilled, pressed and fermented in French oak barriques as unclarified juice, with only wild yeast and a controlled level of oxidative handling.
• Cape Mentelle Heritage Chardonnay 2022: whole bunch pressed, juice transferred to barrel with all the solids for wild fermentation, 38% new French oak barriques, left unsulphured for several weeks post-ferment and matured on lees for 10 months with a stirring regime monitored by tasting.

Barrels are harder to keep clean than tanks. Microorganisms can migrate up to 8 mm into the barrel wood, which makes it more difficult to completely sanitise a barrel than an inert vessel such as a stainless steel tank. Free SO2 should be checked every 3 months, because it declines faster in barrel than in tank due to greater oxygen exposure, and cellar humidity is best kept between 65 and 75%, since lower humidity encourages greater wine evaporation and higher humidity can encourage spoilage microorganisms. With proper maintenance, barrels should easily last and impart oak flavours for five to six years.

• Topping: a new barrel can adsorb 5-6 L of wine and should be re-topped two weeks after being filled, and then every 2-3 months.
• Sanitation: in a study by Edwards and Cartwright (2018), holding water at 70°C for 30 minutes or 80°C for 20 minutes eliminated Brettanomyces yeast from barrel wood at depths of up to 5-9 mm.
• Reduction: when unwanted volatile sulfur compounds are present in a barrel-fermented wine at the end of fermentation, transferring the lees into barrels for 48 hours and then recombining them with the wine eliminated ethyl and methyl mercaptan within 24 hours in a 2001 study by Lavigne-Cruège and Dubourdieu.
• Oxidation: after white wine oxidation problems, Comtes Lafon began rolling barrels instead of using bâtonnage, to avoid introducing more air while still getting the fine lees into suspension.

Primary sources (the Australian Wine Research Institute, WSET, the Margaret River Wine Association, and producers' own sites for their own winemaking): https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-lees-contact/, https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/packaging-operations/barrel-cleaning-storage-and-maintenance/, https://www.awri.com.au/wp-content/uploads/mlf_modulation_AWRI_fact_sheet.pdf, https://www.wsetglobal.com/knowledge-centre/blog/2022/may/24/behind-the-grape-chardonnay-in-the-us, https://www.wsetglobal.com/knowledge-centre/blog/2023/october/03/how-many-wine-types-and-styles-are-there, https://margaretriver.wine/wine-varieties/, https://www.leflaive.fr/en_US/wine/puligny-montrachet, https://www.leflaive.fr/en_US/wine/batard-montrachet, https://www.leflaive.fr/en_US/wine/chevalier-montrachet, https://www.leflaive.fr/en_US/wine/pouilly-fuisse, https://2023.yquem.fr/en, https://www.vassefelix.com.au/chardonnay, https://www.capementelle.com.au/product/2022-Heritage-Chardonnay, https://www.pierro.com.au/post/australian-chardonnay-the-current-scene. Secondary: https://www.decanter.com/wine/producer-profiles/chateau-d-yquem-producer-profile-245936/, https://www.decanter.com/wine-news/reimagining-yquem-us-lighthouses-showcase-chateau-dyquems-new-2020-release-500347/, https://www.decanter.com/wine/producer-profiles/domaine-des-comtes-lafon-producer-profile-245913/, https://www.decanter.com/learn/oak-barrels-335990/, https://www.decanter.com/learn/advice/what-are-lees-in-wine-ask-decanter-377513/, https://www.decanter.com/learn/what-is-sur-lie-ageing-and-what-does-it-do-to-wine-ask-decanter-465202/, https://decanter.com/wine/grape-varieties/semillon-grape-varieties, https://www.burgundy-report.com/burgundy-report-extra/10-2010/profile-domaine-des-comtes-lafon-meursault/. Last verified 2026-10-04