What is wine fermentation?

The short answer

Wine fermentation is the process in which yeast converts grape sugars into alcohol and carbon dioxide. In Prosecco DOC spumante, a second fermentation in a sealed tank produces the retained sparkle. The bubbles get noticed, but the first transformation is juice becoming wine.

Answered by Michael Goldstein · Founder, Bella Principessa
Updated on

The full answer

Wine fermentation is the process in which yeast converts grape sugars into alcohol and carbon dioxide. In Prosecco DOC spumante, a second fermentation in a sealed tank produces the retained sparkle. The bubbles get noticed, but the first transformation is juice becoming wine.

A grape is sweet. Wine contains alcohol. Between those familiar facts is fermentation, the process that makes the change possible.

Yeast uses the sugars in grape juice and produces alcohol, carbon dioxide and other compounds that help shape the wine’s character. It is biology doing something you can eventually taste.

Where does the winemaker come in?

The winemaker manages the conditions, including temperature and preparation of the juice, to achieve the intended style. Calling fermentation natural does not mean the wine makes itself without careful attention.

Our first fermentation guide explains Prosecco’s base-wine stage. That wine is the foundation for what happens next.

Why ferment again for sparkling Prosecco?

For Prosecco DOC spumante, the base wine undergoes a further fermentation in a pressure-resistant tank. Carbon dioxide remains in the wine under pressure and is retained through bottling. This is the Martinotti or Charmat method.

Champagne places its sparkling fermentation in bottles. Both depend on fermentation, with different vessels and production sequences. Our Prosecco and Champagne guide puts the difference in context.

What does this tell you about sweetness?

Fermentation explains what happens to sugar, but the finished wine still needs its own sweetness description. Read Brut, Extra Dry or the other term on the label.

Bella Principessa white and rosé Brut give you two different expressions. Our Prosecco sweetness guide explains the category order, including their shared Brut category. Knowing the process helps you understand the wine; knowing the style helps you choose the one you want to pour.

Sources

Prosecco DOC winemaking.

WSET: sparkling-wine production methods supports the bottle-fermentation comparison.

The long read, in the JournalThe Charmat method: how Prosecco gets its bubbles6 min read →

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More in this topic

Grapes and how it’s made

How is Prosecco made?

Prosecco begins with grapes fermented into base wine. For Prosecco DOC spumante, a second fermentation in sealed pressure tanks creates the bubbles before bottling. This is the Martinotti or Charmat method. The cork gets the applause; the yeast has done the work.

From base wine to bubbles, for white and rosé
What are the main grape varieties used in Prosecco?

Glera is Prosecco’s main grape. White Prosecco DOC requires at least 85% Glera, with other permitted varieties limited to 15% combined. DOC Rosé requires 85–90% Glera and 10–15% Pinot Nero vinified as red wine. White Prosecco can be 100% Glera, so not every bottle is a blend.

Glera, the blend and what each grape adds
What’s So Special About Prosecco Grapes?

Glera, Prosecco's principal grape, contributes acidity and fruit and floral aromas. Growing conditions and winemaking shape how those qualities appear in the glass. Tank fermentation can highlight that fresh character; the grape alone does not explain every difference between bottles.

What Glera adds, and why the growing matters
How old are the origins of the Glera grape variety used to produce Prosecco sparkling wine?

No one can put an exact date on it. The grape behind Prosecco has been grown in northeast Italy for centuries: the wine called "Prosecho" was already famous in 1593, writers linked it to a Roman wine called Pucinum, and the grape is recorded under the name Prosecco in 1772. Since 2009 its official name has been Glera.

From legend to label, and the name change
What other grapes can be used to make Prosecco?

White Prosecco DOC may include up to 15% permitted varieties alongside Glera, including Chardonnay, Pinot Grigio and several local grapes. Rosé follows a different rule: Glera with Pinot Nero vinified as red wine. The permitted list describes possibilities, not the recipe of every bottle.

The permitted grapes, and red grapes in white wine
How are Prosecco’s Glera grapes harvested?

Glera grapes are harvested when their ripeness suits the intended Prosecco, balancing sugar, acidity and grape condition. The date varies with the site and season. Picking methods vary too, so a photograph of a hillside harvest does not describe every bottle on the shelf.

When the grapes are picked, and whether by hand
What is Prosecco grape harvest yield?

Harvest yield measures grapes grown per area. The Prosecco DOC specification lists a base maximum of 18 tonnes per hectare for Glera and 13.5 for Pinot Nero used in rosé. These are regulatory limits, not actual vineyard averages; harvest-year measures can affect what is permitted.

The DOC limits and grape-to-wine yield
What is Prosecco grape pressing?

Prosecco grape pressing extracts the juice, called must, that will become wine. For white-wine production, gentle pressing separates juice from grape skins before fermentation. The juice then settles so the cellar can separate it from suspended solids.

What pressing does, and when the bubbles form
What is Prosecco’s first fermentation?

Prosecco’s first fermentation turns grape juice into base wine as yeast converts sugar into alcohol. For DOC spumante, a later fermentation retains the bubbles. First comes the wine; the entrance comes later.

From juice to base wine, for white and rosé
What is the Martinotti method?

The Martinotti method, also called Charmat or the tank method, gives Prosecco DOC spumante its bubbles through a second fermentation in a sealed pressure tank. Yeast produces carbon dioxide, which stays in the wine under pressure. Three names, one useful idea: keep the gas in the wine.

How the pressure tank works, for white and rosé
What are the methods of making sparkling wine?

Sparkling-wine techniques include the traditional method, tank method and ancestral method. They differ in where fermentation happens and how carbon dioxide is retained. A similar stream of bubbles can conceal a rather different cellar story.

Bottle, tank and ancestral methods compared
How are the bubbles in Prosecco formed?

Prosecco’s bubbles come from carbon dioxide made by fermentation. In Prosecco DOC spumante, a second fermentation in a sealed tank retains the gas under pressure. Opening the bottle releases that pressure, letting the bubbles appear and rise through your glass.

How fermentation makes them, and why they fade
What is wine terroir?

Wine terroir describes the growing environment behind a wine, including climate, soil and the vineyard's physical setting. It helps explain why the same grape can make different wines in different places. It is a useful idea about growing conditions, not a claim that you are literally tasting a handful of soil.

Place, people and what it means for Prosecco
What are tannins?

Wine tannins are natural plant compounds called polyphenols that contribute a drying or gripping sensation in the mouth. They come from grape skins, seeds, stems and sometimes oak. Tannin grip differs from low sugar and acidity: a dry wine can have little noticeable tannin.

Where they come from, and whether Prosecco has them

All 113 Prosecco questions →

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