The Overview
How Is Sparkling Wine Made? Explained Simply
Sparkling wine is made in two steps: first, grapes become a still base wine, then this wine ferments a second time in a sealed vessel. The carbon dioxide from this fermentation can't escape and dissolves into the wine. Whether this happens in the bottle or in a tank shapes the style, the effort involved, and the label.
Where Do the Bubbles in Sparkling Wine Come From?
Every wine fermentation produces carbonic acid. Yeasts consume the sugar in grape juice and turn it into alcohol and carbon dioxide, a gas that fizzes as carbonic acid once dissolved in wine. With still wine, it escapes through open fermentation bungs into the air, which is why cellars smell of yeast and fresh bread in autumn. For sparkling wine, the cellar master flips this principle: fermentation takes place in a sealed vessel instead. The gas finds no way out, pressure builds, and the carbon dioxide dissolves into the wine.
This balance only tips when the bottle is opened. Pressure drops suddenly, the dissolved gas wants out, and bubbles form on tiny imperfections in the glass. EU law requires that for sparkling wine, Sekt, and semi-sparkling wine without additives, the carbonic acid must come from fermentation. The cuvée may only ferment in bottles or in a pressurized tank, which the law calls a cuvée tank. How much pressure ends up in the bottle, and what it depends on, is explained in the final stop of this journey.
Step One: A Base Wine With Plenty of Acidity
It all starts with a wine you'd barely want to drink on its own. The grapes are picked earlier than for still wine, because the base wine needs crisp acidity and shouldn't bring too much alcohol to the table. The second fermentation adds a bit more alcohol on top, and carbonic acid intensifies every impression of acidity and bitterness on the palate. A heavy, very ripe wine would taste clumsy and flat as a sparkling wine.
The cellar master blends these base wines into the cuvée, the term for the finished blend before the second fermentation. It can contain wines from different vineyard sites, grape varieties, and vintages. At large houses, this blend determines whether the sparkling wine tastes consistent year after year. With grower Sekt, by contrast, a single grape variety from one vintage is often the focus. How picking, pressing, and blending actually work is covered in the stop on base wine and cuvée.
Step Two: Fermentation in the Bottle or in the Tank?
For the second fermentation, the cuvée receives sugar and yeast. From here, the paths diverge. In traditional bottle fermentation, each bottle ferments on its own, the yeast lees stay inside for months, and are eventually removed through the neck of the bottle. This is how Champagne, Crémant, Cava, Franciacorta, and grower Sekt are made. In the transfer method, the wine also ferments in the bottle but is then transferred under pressure into a tank, filtered, and rebottled.
Tank fermentation moves the second fermentation into a large pressurized stainless steel tank. It's faster, requires less manual work, and preserves the grape's fruit aromas noticeably well. Prosecco is usually made this way, as are many large branded sparkling wines. A fourth path skips the second fermentation entirely: with méthode ancestrale, Pét-Nat, and Asti, the first fermentation simply finishes inside the sealed vessel. None of these methods is automatically superior. Each serves a different style, and each gets its own stop on this journey.
What Does the Label Reveal About Production?
Whether a sparkling wine was fermented in the bottle is only revealed on the label. If there's no mention at all, it very likely came from a tank. The term "bottle fermented" also permits the bottle-to-bottle transfer method. Only "traditional bottle fermentation" or "classic bottle fermentation" guarantees that the wine spent at least nine months continuously on the lees at the same producer and is sold in the very bottle in which it fermented. What these terms legally require in detail is covered in the journey through law and labeling.
A special case is sparkling wine that simply has carbon dioxide added to it, much like sparkling mineral water. EU law lists it as its own category, "sparkling wine with added carbon dioxide." It may only be made from wine without protected origin status, and the label must carry the statement "made by the addition of carbon dioxide." It may not be sold as quality sparkling wine, and therefore not as Sekt, since that category requires the carbonic acid to come from fermentation. The same divide applies to semi-sparkling wine: semi-sparkling wine with added carbon dioxide is its own category.