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. Decanter notes that many of the world's greatest white wines ferment and mature in oak casks, and that the work is labour intensive. WSET says Californian Chardonnay is renowned for making full use of malolactic fermentation, lees contact, and oak barrel fermentation and maturation. Decanter's Semillon guide notes that the Semillon and Sauvignon Blanc dry whites of Pessac-Léognan are often barrel-fermented.

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

Settled and racked grape juice is transferred directly into barrels where fermentation begins, either spontaneously with indigenous yeasts or after inoculation with selected strains. Domaine Leflaive describes decanting over 24 hours, then racking and running into barrels, and Pierro ferments its VR Reserve Chardonnay juice in French oak barriques using a mix of natural and cultured yeasts; Vasse Felix instead ferments unclarified juice, and Cape Mentelle transfers its Heritage Chardonnay juice to barrel with all the solids. 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, as Decanter explains. Oxygen enters through the barrel staves and the bunghole, and the AWRI notes that lees can scavenge it, especially when they are stirred. After primary fermentation, malolactic fermentation may follow in the same barrel, and the wine may remain on its fine lees, which add textural richness through autolysis.

• Lees contact throughout fermentation and élevage adds textural weight and complexity; bâtonnage (lees stirring) is used selectively at Domaine des Comtes Lafon, where Decanter reported in 2017 that lees-stirring is used sparingly.
• The AWRI recommends a small amount of stirring at the end of fermentation, because stirring encourages continued yeast cell viability, which encourages the assimilation of any residual sugar.
• The AWRI warns that excessive stirring can introduce too much oxygen, leading to the loss of SO2 and potentially acetaldehyde and acetic acid; in a Brajkovich (2008) trial it cites, the barrel-fermented Chardonnay that was neither stirred nor topped was preferred after four months.
• Decanter reports that 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.

Decanter explains that 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. The AWRI lists the reported benefits of lees contact as "increased texture; greater oak, fruit, and yeast integration; more complexity; and improved oak aromas and flavours". WSET says 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. Decanter quotes Jean-François Coche-Dury, who believes intimate contact between wine and lees is critical to quality: "The wines acquire strength and structure, muscles and sinew".

• The AWRI says one of the major compounds produced by Oenococcus oeni during malolactic fermentation is diacetyl, which contributes buttery or butterscotch aroma, and that butteriness can be masked by strong oak or very fruity characters.
• In the AWRI's table of malolactic winemaking techniques, long yeast lees contact is linked to a lower diacetyl concentration.
• Decanter's sur lie guide says lees contribute to a buttery mouthfeel, increased complexity and aromas like brioche and toasted nuts, and that mannoproteins reduce tartrate precipitation and promote protein stability.
• Decanter describes Semillon in Bordeaux blends with Sauvignon as 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, the Margaret River Wine Association says 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. WSET notes that inexpensive to mid-priced Central Valley Chardonnay in California is likely to get any oak influence from oak chips or staves, and that 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 Decanter reported in 2017 that at Domaine des Comtes Lafon in Meursault the white wines, like the reds, are fermented with natural yeasts.
• Sauternes: Decanter reported in 2023 that 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: the Margaret River Wine Association says 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: WSET says 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, Decanter reported in 2017 that Montrachet is the only wine aged entirely in new oak and that the premiers crus are aged in a proportion that varies from 25% to 40% and stay in wood for 16 months. In Sauternes, Château d'Yquem's 2023 is 70% Sémillon and 30% Sauvignon Blanc (Yquem); Decanter reported in 2019 that ageing had been reduced from at least 36 months in new oak under Lur-Saluces to no more than 30 months, and in 2023 that 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 (Pierro).

• Domaine des Comtes Lafon: Dominique Lafon told Decanter in 2017 that lees-stirring is used "usually when the fermentation is slow to finish or when the wine is reduced"; Decanter adds that his cellars are notoriously cold, so fermentations can be slow.
• Château d'Yquem: Pasquini told Decanter 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 (Vasse Felix).
• 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 (Cape Mentelle).

Barrels are harder to keep clean than tanks. The AWRI notes that 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. It advises checking free SO2 every 3 months, because it declines faster in barrel than in tank due to greater oxygen exposure, and keeping cellar humidity between 65 and 75%, since lower humidity encourages greater wine evaporation and higher humidity can encourage spoilage microorganisms. With proper maintenance, the AWRI says, barrels should easily last and impart oak flavours for five to six years.

• Topping: the AWRI says 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: the AWRI cites Edwards and Cartwright (2018), who found that 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, the AWRI reports that transferring the lees into barrels for 48 hours and then recombining them with the wine eliminated ethyl and methyl mercaptan within 24 hours (Lavigne-Cruège and Dubourdieu 2001).
• Oxidation: Burgundy Report noted in 2010 that after white wine oxidation problems, Comtes Lafon began rolling barrels instead of 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 2026-09-28