Sparkling Wine: How the Bubbles Get In

WSET explains that 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, "there’s nowhere for the CO2 to go": it dissolves within the wine. Wine Australia's educator guide describes the release: when the bottle is opened, the drop in pressure turns the dissolved carbon dioxide back into a gas, and the wine bubbles. Champagne.fr puts the pressure inside a bottle of Champagne at 5 to 6 bar, about three times the pressure of a car tyre, and WSET notes that sparkling wine bottles are made from thicker, heavier glass than still wine bottles to contain the carbon dioxide. What separates the methods is where the gas is trapped (in a bottle or in a tank), whether the wine goes through one fermentation or two, and how long it then spends on its lees. One route skips fermentation altogether: carbonation, which Wine Australia calls 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", and Wine Australia notes that in Australia a wine can carry 'sparkling' on the label only if its carbon dioxide comes from fermentation.

• Bubbles are carbon dioxide from fermentation, dissolved into the wine because the bottle or tank is sealed.
• Champagne.fr: the pressure inside a bottle of Champagne is 5 to 6 bar, about three times that of a car tyre.
• WSET describes tank method wines as typically having softer bubbles.
• Carbonation injects carbon dioxide into a chilled base wine; US rules call the result carbonated grape wine, not sparkling wine.

WSET defines traditional method sparkling wines 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. Champagne.fr describes the next stage, 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. WSET notes that the bottle is sealed with a crown cap, and Wine Australia's guide says this secondary fermentation takes four to six weeks and increases the alcohol content by 1.3 to 1.5%. As fermentation finishes, the yeast cells die and form lees. Over time the lees break down in a process known as autolysis, which WSET links to 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. 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, champagne.fr says 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.

• WSET names Champagne, French Crémant, Spain's Cava and Corpinnat, Italy's Franciacorta and Trento DOC, English sparkling wine, and South Africa's Cap Classique as traditional method wines.
• Lees ageing and autolysis bring aromas such as brioche, toast, pastry and cream; the longer on lees, the more intense and complex the flavours (WSET).
• Riddling gathers the sediment in the neck; disgorgement freezes it into a plug that the bottle's own pressure expels.
• Champagne minimums (champagne.fr): 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 WSET notes it takes place in a sealed stainless-steel tank rather than in bottle. Italian Wine Central's glossary gives metodo Martinotti as another name for it, especially in Piemonte. Decanter reports that Federico Martinotti, from the province of Asti, invented the tank method for controlled fermentation in large vats in 1895, and that fifteen years later Eugène Charmat developed the autoclave design that is still used today. Wine Australia's educator guide sets out the steps: 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. These wines tend to spend less time on lees than bottle-fermented sparkling wines, which the guide says leaves them little or no autolytic character; WSET says the focus is on preserving primary fruit and aromatic freshness. WSET describes tank method wines as typically 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: Decanter notes that its grape must is fermented only once, in pressurised autoclaves, a single fermentation that retains the aromatic fruity freshness of the Moscato grape.

• WSET examples: 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 (Wine Australia).
• Little or no time on lees keeps the focus on primary fruit and aromatic freshness.
• Faster production and lower labour requirements make tank method wines generally more affordable (WSET).

Wine Australia's educator guide describes the transfer method as 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 guide notes that the majority of Australian sparkling wine production uses this method, as it is less labour-intensive yet still produces high-quality wines. The label can give it away: 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. Champagne cannot be made this way, because champagne.fr states that 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.
• 'Bottle-fermented' on a label, as opposed to 'fermented in this bottle', points to the transfer method (Wine Australia).
• The majority of Australian sparkling wine production uses the transfer method (Wine Australia).

WSET calls the ancestral method the oldest way of making sparkling wine and says it is often labelled as pét-nat (pétillant naturel) today. The wine is bottled while still undergoing its first fermentation, trapping the carbon dioxide. Wine Australia's educator guide describes one way to do it. 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 the guide calls the ancestral method the most difficult to control. WSET describes ancestral-method wines as typically 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 (WSET).
• Limoux méthode ancestrale comes from a first fermentation completed in bottle (INAO).
• WSET names Col Fondo Prosecco, bottled with its lees, as a related style.

Disgorgement costs a little wine: champagne.fr notes that 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. Champagne.fr describes the liqueur de dosage as cane sugar dissolved in wine, approximately 1cl for a 75cl bottle of Champagne brut. WSET says 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, champagne.fr gives these bands: 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. WSET's list of sparkling wine terms adds Extra Brut, at 0 to 6 g/L, between Brut Nature and Brut. As WSET points out, 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: champagne.fr says that a very neutral liqueur keeps as much of the wine's personality as possible, while a liqueur containing reserve wine adds other aromas. In Wine Australia's step sequences for the tank and transfer methods, dosage comes after filtering and before bottling.

• Driest to sweetest (WSET): Brut Nature or Zero Dosage (0 to 3 g/L), Extra Brut (0 to 6), Brut (0 to 12), Extra Dry or Extra Sec (12 to 17), Sec (17 to 32), Demi-Sec (32 to 50), Doux (50 and above).
• Extra Dry is sweeter than Brut (WSET).
• A Champagne brut takes approximately 1cl of liqueur de dosage per 75cl bottle (champagne.fr).
• In the tank and transfer methods, dosage is added after filtering and before bottling (Wine Australia).

WSET says tank method wines are generally more affordable due to faster production and lower labour requirements. Wine Australia's guide calls carbonation the least expensive way to produce sparkling wine, and says 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 champagne.fr says that in practice this timeframe is nearly always longer: 2 to 3 years for non-vintage wines and 4 to 10 years for vintage Champagne. Those years show in the glass, since WSET notes that the longer the wine remains on its lees, the more intense and complex the autolytic flavours become. Wine Australia says maturation on lees can last from at least nine months to several years, varying from region to region, and calls it essential for determining the flavours and style of the wine. Labour adds to the bill: champagne.fr puts manual remuage at 4 to 6 weeks, although riddling is usually automated today.

• Champagne's minimums are 15 months, and three years for vintage; in practice champagne.fr says 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 (WSET).
• Longer lees ageing brings more intense and complex autolytic flavours (WSET).
• Carbonation is the least expensive way to produce sparkling wine (Wine Australia).

Primary sources (WSET, champagne.fr, the US eCFR, Wine Australia and INAO), with Italian Wine Central and Decanter as secondary sources: 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. Last verified 2026-09-28