What Is Carbon Dioxide in Wine? A Beginner’s Guide

Quick answer: what is carbon dioxide in wine?

Carbon dioxide in wine is the gas produced when yeast ferments grape sugar. During alcoholic fermentation, yeast converts sugar into ethanol, carbon dioxide and heat.

In many wines, much of the CO₂ escapes during fermentation. Some remains dissolved in the liquid, however. When that dissolved gas is released in the glass, it can create a light fizz or a slightly prickly sensation known as spritz.

Sparkling wine retains substantially more CO₂, usually under pressure, so it produces a stronger and more persistent stream of bubbles. The gas may come from a secondary fermentation in the bottle, a secondary fermentation in a closed tank, or fermentation that finishes in the bottle, as with many pét-nat styles.

CO₂ is therefore both a natural part of winemaking and a major contributor to the way some wines look, feel and taste.

How does yeast create CO₂?

Alcoholic fermentation is one of the central stages of how wine is made. Yeast feeds on fermentable grape sugars and produces ethanol, carbon dioxide and heat.

You can think of it as:

grape sugar → alcohol + carbon dioxide + heat

The CO₂ is a gas. If fermentation takes place in a vessel that allows gas to escape, much of it leaves the wine. If the wine is kept in a sealed, pressure-capable environment, more CO₂ can remain dissolved.

Temperature, agitation, pouring and time all affect how much gas stays in solution. Cooler wine generally holds dissolved gas more readily than warmer wine, while movement and warming encourage it to escape. This is why a wine may seem more spritzy immediately after opening or pouring, then become calmer in the glass.

For a closer look at the process, see what fermentation means in wine and what yeast does in wine.

What is spritz in still wine?

Spritz is a light, fine fizz or prickly sensation caused by dissolved CO₂. It is a word you may hear in an Australian tasting room or bottle shop.

Still wine can contain dissolved CO₂. Wine Australia research describes it as a standard feature of still wines and reports approximately 0.5–1 gram per litre as typical context for still bottled white wines. That is not a universal specification for every still wine, but it helps explain why “still” does not necessarily mean “contains absolutely no dissolved gas”.

A small amount of spritz may add lift and liveliness. It can make a wine feel fresh or energetic, particularly when served cold. Some winemakers may choose to retain a noticeable amount because it contributes to the wine’s intended texture.

The important point is that spritz is not automatically a fault. A wine with a little prickliness may be deliberately made that way, may simply retain ordinary dissolved gas, or may require further investigation if the bubbles are persistent and unexpected.

Why does sparkling wine have more bubbles?

Sparkling wine contains much more retained CO₂ than ordinary still wine. The gas is kept in the wine under pressure, ready to come out as bubbles when the bottle is opened and the wine is poured.

The main production routes are:

• Traditional method: a secondary fermentation takes place in the bottle.
• Tank method: a secondary fermentation takes place in a closed tank before bottling.
• Ancestral method: wine is bottled before fermentation is complete, allowing remaining sugar to generate CO₂ in the bottle.

These methods create different styles, but their shared feature is retained carbon dioxide. You can learn more in the guides to sparkling wine, traditional-method production, tank-method production and ancestral-method production.

In Australian labelling guidance, sparkling wine is distinguished from wine made effervescent by adding CO₂. If you are reading a label, “sparkling” and “carbonated” should not be treated as interchangeable terms.

How does CO₂ affect the way wine tastes?

CO₂ can affect wine in several noticeable ways:

• Bubbles: the most obvious visual and physical effect.
• Prickliness: a tingling sensation on the tongue.
• Texture: CO₂ can make wine feel lighter, livelier or more energetic.
• Aroma movement: rising bubbles help move wine aromas towards the surface.
• Perceived freshness: spritz can add a sense of lift, although freshness also depends on acidity, fruit, alcohol, sweetness and temperature.

CO₂ does not have one fixed sensory effect in every wine. Research has found that dissolved CO₂ can influence perceptions such as bitterness, sweetness and astringency, but the result depends on the wine and the amount of gas present. It is more accurate to say that CO₂ can influence perception than that it always makes wine sweeter, fresher or less bitter.

Fine, persistent and well-integrated bubbles are generally desirable in sparkling wine. In a still wine, the ideal amount depends on the wine’s intended style.

CO₂ is not sweetness, acidity or sulphur dioxide

Carbon dioxide is a separate component from several wine terms that beginners commonly confuse:

• Sweetness comes mainly from residual sugar, not from CO₂.
• Acidity describes the wine’s acids and their effect on taste. CO₂ can make a wine feel more lively, but it is not the same as chemical acidity.
• Oxygen is a different gas. Oxygen exposure can change wine in ways that are separate from dissolved CO₂.
• Sulphur dioxide, often written as SO₂, is a separate winemaking compound with different uses. It is not another name for carbon dioxide.

For that last distinction, see sulphur dioxide in wine.

Carbon dioxide is also not the same as carbonic maceration. Carbonic maceration is a distinct whole-bunch red-winemaking process, not simply wine containing dissolved CO₂. Read more about carbonic maceration if the terms have become muddled.

Are bubbles in still wine a fault?

Not necessarily. When you open a still wine, look at the character of the bubbles rather than jumping to a diagnosis.

Brief, fine bubbles that fade after pouring may simply be dissolved CO₂. Persistent bubbling, pressure, sweetness, sediment or unusual aromas may suggest that fermentation has continued or that another quality issue is present. But bubbles alone cannot establish the cause.

A practical approach is to observe:

1. Whether the fizz is brief or continues.
2. Whether the wine tastes unexpectedly sweet.
3. Whether there is unusual pressure when opening the bottle.
4. Whether the aroma and flavour seem sound.
5. Whether the label or producer description suggests a lightly spritzy style.

If the wine seems unstable or unpleasant, set it aside and seek advice from the retailer or producer. The key lesson is simple: a little spritz can be intentional, while unexpected persistent bubbles deserve attention.

The takeaway

Carbon dioxide begins as a natural product of fermentation. Winemakers may allow most of it to escape, retain some for spritz, or preserve much more of it under pressure to make sparkling wine.

When you notice bubbles, ask what role they are playing. Are they adding gentle lift to a still wine? Are they creating the persistent effervescence expected in sparkling wine? Or are they unusual enough to warrant a closer look?

That question will take you further than assuming every bubble is either a sign of quality or a sign of trouble.