Sparkling Wine: How the Bubbles Get In

When yeast ferments sugar in a tightly sealed bottle, it creates a little more alcohol and some carbon dioxide, and because the bottle is sealed, as WSET puts it, "there’s nowhere for the CO2 to go": it dissolves within the wine. When the bottle is opened, the drop in pressure turns the dissolved carbon dioxide back into a gas, and the wine bubbles. The pressure inside a bottle of Champagne is 5 to 6 bar, about three times the pressure of a car tyre, and sparkling wine bottles are made from thicker, heavier glass than still wine bottles to contain the carbon dioxide. One route works differently: carbonation, the least expensive way to produce sparkling wine, injects carbon dioxide into a chilled base wine. The rules keep it separate. Under US federal regulation 27 CFR 4.21, wine made effervescent with carbon dioxide other than that resulting solely from the secondary fermentation of the wine within a closed container, tank or bottle is "carbonated grape wine". In the EU, Regulation (EU) No 1308/2013 defines sparkling wine as the product obtained by a first or second alcoholic fermentation from fresh grapes, grape must or wine, that releases carbon dioxide derived exclusively from fermentation when opened and has an excess pressure of not less than 3 bar at 20 °C in closed containers (3.5 bar for quality sparkling wine), while aerated sparkling wine releases carbon dioxide derived wholly or partially from an addition of that gas. Under Delegated Regulation (EU) 2019/934, that fermentation may take place only in bottles or in closed tanks.

• Bubbles are carbon dioxide from fermentation, dissolved into the wine because the bottle or tank is sealed.
• The pressure inside a bottle of Champagne is 5 to 6 bar, about three times that of a car tyre.
• Tank method wines typically have softer bubbles.
• Carbonation injects carbon dioxide into a chilled base wine; US rules call the result carbonated grape wine, not sparkling wine.
• In the EU, sparkling wine must get its carbon dioxide only from fermentation; aerated sparkling wine is the EU term for a product that releases carbon dioxide derived wholly or partially from an addition of that gas.

Traditional method sparkling wines are defined by a second fermentation inside the bottle, followed by ageing on the lees; it is the method used for Champagne. Production begins with a still base wine, which may be a blend of different grape varieties, vineyard sites and vintages. Next comes the prise de mousse, which literally means capturing the sparkle: a liqueur de tirage, a mixture of still wine, sugar and yeast, is added at bottling, and the yeast consumes the sugar, releasing alcohol and bubbles. The bottle is sealed with a crown cap, and this secondary fermentation takes four to six weeks and increases the alcohol content, which Wine Australia puts at 1.3 to 1.5%. In the EU, adding the tirage liqueur may not raise the total alcoholic strength of the cuvée by more than 1.5% vol. As fermentation finishes, the yeast cells die and form lees. Over time the lees break down in a process known as autolysis, which can bring aromas such as brioche, toast, pastry and cream; the longer the wine remains on its lees, the more intense and complex these flavours become. Champagne sets firm rules around this stage: bottling cannot take place before the first day of January following the harvest, the wine is sold in the bottle in which it underwent its second fermentation, and all Champagnes must spend at least 15 months maturing in the cellar before release, with vintage cuvées matured for at least three years. Cava follows the traditional method too, with its second fermentation in the same bottle that reaches the consumer, and the Cava DO sets minimum ageing periods of 9 months for Cava de Guarda, 18 months for Reserva, 30 months for Gran Reserva and 36 months for Cava de Paraje Calificado. Then the sediment has to come out. Riddling (remuage) rotates each bottle in small increments while gradually tilting it neck-down, so the sediment slides into the neck. By hand, on wooden racks called pupitres, remuage takes 4 to 6 weeks and on average 25 turns per bottle; today riddling is usually automated, with machines that process racks of 500 bottles in a single operation and take one week instead of six. At disgorgement the bottle neck is plunged into a solution at approximately -27°C, which freezes the sediment into a plug, and when the bottle is opened the pressure built up inside expels it. The bottle is then topped up with the dosage and sealed with a cork held in place by a wire cage, or muselet.

• Traditional method wines include Champagne, French Crémant, Spain's Cava and Corpinnat, Italy's Franciacorta and Trento DOC, English sparkling wine, and South Africa's Cap Classique.
• Lees ageing and autolysis can bring aromas such as brioche, toast, pastry and cream; the longer on lees, the more intense and complex the flavours.
• Riddling gathers the sediment in the neck; disgorgement freezes it into a plug that the bottle's own pressure expels.
• Champagne minimums: at least 15 months maturing in the cellar for all Champagnes, at least three years for vintage cuvées.

The tank method, also known as the Charmat or cuve close method, also involves a second fermentation, but it takes place in a sealed stainless-steel tank rather than in bottle. Especially in Piemonte, it also goes by metodo Martinotti. According to Decanter, Federico Martinotti, from the province of Asti, invented the tank method for controlled fermentation in large vats in 1895, and fifteen years later Eugène Charmat developed the autoclave design that is still used today. The steps run like this: the dry base wine moves to a pressurised tank, the winemaker adds sugar and yeast to start the second fermentation and seals the tank so the carbon dioxide dissolves into the wine, and when the second fermentation finishes the wine is filtered and bottled under pressure. For Prosecco DOC Frizzante and Spumante, this second fermentation happens in big tanks called autoclaves and, according to the Prosecco DOC Consorzio's winemaking page, lasts at least 30 days, or at least 60 days for the rosé. EU rules for quality sparkling wine with a protected designation of origin set the fermentation and the time on the lees at no less than 90 days, or 30 days if the fermentation takes place in containers with stirrers. These wines tend to spend less time on lees than bottle-fermented sparkling wines, which leaves them little or no autolytic character; the focus is on preserving primary fruit and aromatic freshness. Tank method wines tend to be light, fresh and fruit-driven, with softer bubbles, designed to be consumed young and generally more affordable due to faster production and lower labour requirements. Common grape varieties include Glera (Prosecco), Moscato, Riesling and the various Lambrusco grapes. Asti is a variation: its grape must is fermented only once, in pressurised autoclaves, a single fermentation that retains the aromatic fruity freshness of the Moscato grape.

• Examples include Prosecco DOC and Prosecco DOCG, Asti Spumante and Moscato d'Asti, German Sekt made from Riesling, and Australian sparkling Shiraz.
• The second fermentation happens in a sealed, pressurised tank; the wine is then filtered, dosed and bottled under pressure.
• Little or no time on lees; the focus is on preserving primary fruit and aromatic freshness.
• Faster production and lower labour requirements make tank method wines generally more affordable.

The transfer method is a way to achieve the benefits of a second fermentation in the bottle without the complications and expense of the traditional method's riddling and disgorgement. Until the riddling stage, the traditional and transfer methods are the same: tirage, second fermentation in bottle and maturation on lees. Then the paths split. After its time on lees, the wine is removed from the bottle and transferred to a tank, filtered in bulk to remove the yeast, dosed and pumped into new bottles. The majority of Australian sparkling wine production uses this method, as it is less labour-intensive yet still produces what Wine Australia calls high-quality wines. In Australia, Wine Australia's educator guide gives a label clue: a wine that claims to be 'bottle-fermented' as opposed to 'fermented in this bottle' was made by the transfer method rather than the traditional method. For Champagne, the wine cannot be transferred from one container to another and is sold in the bottle in which it underwent its second fermentation.

• Identical to the traditional method up to riddling: second fermentation and lees ageing happen in bottle.
• Instead of riddling and disgorging each bottle, the wine is emptied into a tank, filtered in bulk, dosed and pumped into new bottles.
• The majority of Australian sparkling wine production uses the transfer method.

The ancestral method is the oldest way of making sparkling wine, and today it is often labelled as pét-nat (pétillant naturel). The wine is bottled while still undergoing its first fermentation, trapping the carbon dioxide. In one approach, the first fermentation is arrested about halfway through by chilling the tank, a coarse filtration may remove some of the yeasts, and the partially fermented wine is transferred to sparkling wine bottles and sealed, in Australia often under crown cap. As the wine warms up, the remaining yeasts resume fermentation and the carbon dioxide is trapped in the bottle. In that version the wine is not riddled or disgorged, so it is cloudy, and Wine Australia calls the ancestral method the most difficult to control. Ancestral-method wines tend to be lightly sparkling, softly textured and fruit-driven, often sealed with crown caps and closely associated with minimal-intervention and natural winemaking, with modern pét-nats made around the world in every colour and style. In France, INAO draws the same line inside one appellation, distinguishing Limoux's sparkling wines made by a second fermentation in bottle, Blanquette de Limoux, from those made by a first fermentation completed in bottle, Limoux méthode ancestrale. For the Limoux sparkling wines, recognised as an appellation in 1938, INAO's page names Mauzac, which it calls "le cépage ancestral".

• The wine is bottled before its first fermentation finishes, and the carbon dioxide from the rest of that fermentation is trapped in the bottle.
• Pét-nats usually contain lees, giving them a cloudy appearance.
• Limoux méthode ancestrale comes from a first fermentation completed in bottle.
• Col Fondo Prosecco, bottled with its lees, is a related style.

Disgorgement costs a little wine: when the bottle is opened, a small amount of wine is forced out with the sediment. The bottle is then topped up with the dosage. The liqueur de dosage is cane sugar dissolved in wine, approximately 1cl for a 75cl bottle of Champagne brut. Dosage adjusts the final sweetness level and plays an important role in balancing acidity and overall style. The amount of sugar decides the label term. For Champagne, the bands are: brut nature, less than 3 grams of sugar per litre with no sugar added; brut, less than 12; extra dry, 12 to 17; sec, 17 to 32; demi-sec, 32 to 50; and doux, more than 50. Champagne also has extra brut, between 0 and 6 grams. In the EU these are the legal sugar terms for sparkling wine, set by Delegated Regulation (EU) 2019/33 (Article 47 and Annex III Part A): brut nature under 3 g/L, used only where no sugar has been added after the secondary fermentation; extra brut 0 to 6; brut under 12; extra dry 12 to 17; sec 17 to 32; demi-sec 32 to 50; and doux over 50. The sugar content may not differ by more than 3 g/L from what appears on the label. Cava labels use Spanish names for the same bands (Extra Seco 12 to 17 g/L, Seco 17 to 32, Semi Seco 32 to 50, Dulce over 50), and Prosecco DOC Spumante calls the 17 to 32 g/L band Dry. Extra Dry is sweeter than Brut, a term most commonly seen on Prosecco labels. Dosage is a style choice as well as a sweetness setting: a very neutral liqueur keeps as much of the wine's personality as possible, while a liqueur containing reserve wine adds other aromas. In the tank and transfer methods, dosage comes after filtering and before bottling.

• EU legal sugar terms (Delegated Regulation (EU) 2019/33), driest to sweetest: brut nature or dosage zéro (under 3 g/L, no sugar added after the secondary fermentation), extra brut (0 to 6), brut (under 12), extra dry or extra sec (12 to 17), sec (17 to 32), demi-sec (32 to 50), doux (over 50).
• Extra Dry is sweeter than Brut.
• A Champagne brut takes approximately 1cl of liqueur de dosage per 75cl bottle.
• In the tank and transfer methods, dosage is added after filtering and before bottling.

Tank method wines are generally more affordable due to faster production and lower labour requirements. Carbonation is the least expensive way to produce sparkling wine, and the transfer method exists to avoid the complications and expense of riddling and disgorgement. Champagne's statutory minimums are 15 months in the cellar for all Champagnes and three years for vintage cuvées, and in practice this timeframe is nearly always longer: 2 to 3 years for non-vintage wines and 4 to 10 years for vintage Champagne. Maturation on lees can last from at least nine months to several years, varying from region to region, and is essential for determining the flavours and style of the wine. Manual remuage takes 4 to 6 weeks, although riddling is usually automated today.

• Champagne's minimums are 15 months, and three years for vintage; in practice the time is 2 to 3 years for non-vintage and 4 to 10 years for vintage.
• Tank method wines are faster to produce and need less labour, which keeps them generally more affordable.
• Longer lees ageing brings more intense and complex autolytic flavours.
• Carbonation is the least expensive way to produce sparkling wine.

Primary sources (WSET, champagne.fr, the US eCFR, EUR-Lex, the Prosecco DOC consortium, the Cava DO, Wine Australia and INAO), with Italian Wine Central and Decanter as secondary sources: https://italianwinecentral.com/glossary-alphabetical/, https://www.decanter.com/premium/asti-and-moscato-dasti-experts-choice-462890/, https://www.wsetglobal.com/knowledge-centre/blog/2026/a-guide-to-sparkling-wine-production-methods-and-regional-styles, https://www.wsetglobal.com/knowledge-centre/blog/2021/october/19/making-traditional-method-sparkling-wines, https://www.champagne.fr/en/about-champagne/how-champagne-is-made/bottling-and-second-fermentation, https://www.champagne.fr/en/about-champagne/how-champagne-is-made/riddling, https://www.champagne.fr/en/about-champagne/how-champagne-is-made/disgorgement, https://www.champagne.fr/en/about-champagne/how-champagne-is-made/dosage, https://www.champagne.fr/en/about-champagne/how-champagne-is-made/maturation, https://www.champagne.fr/en/champagne-frequently-asked-questions, https://www.ecfr.gov/api/versioner/v1/full/2026-09-01/title-27.xml?part=4&section=4.21, https://www.wineaustralia.com/getmedia/bcb47737-a5c2-4eef-b16a-5afa52029a31/AWD-Sparkling-Wines-Educator-guide.pdf?ext=.pdf, https://www.inao.gouv.fr/produit/limoux-methode-ancestrale-9587, https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32019R0033, https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32013R1308, https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32019R0934, https://www.prosecco.wine/en/prosecco/discover/types/, https://www.prosecco.wine/en/prosecco/discover/winemaking/, https://www.cava.wine/es/origen/elaboracion-del-cava/, https://www.cava.wine/es/categorias-tipos-de-cava/brut-nature/, https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:02019R0934-20241229. Last verified 2026-11-09