Carbonic maceration: what it means in winemaking

Quick answer: what is carbonic maceration?

Carbonic maceration is a winemaking method in which intact grapes—usually whole bunches—are placed in a closed vessel containing carbon dioxide and very little oxygen.

Because the berries are still unbroken, their early transformation happens partly inside the fruit. Enzymes drive a short-lived intracellular fermentation, producing a small amount of alcohol and changing some acids and aroma compounds. The grapes are then crushed or pressed, and ordinary yeast-driven alcoholic fermentation usually completes the wine.

That sequence matters. Carbonic maceration is not simply “fermentation without yeast”. Yeast may ferment juice released by broken berries during the treatment, and yeast fermentation normally plays the main role in completing the wine.

How does the process work?

A simplified sequence looks like this:

1. Intact fruit enters the vessel. Handling aims to keep the berries from breaking.
2. The atmosphere becomes oxygen-limited. Carbon dioxide may be added or produced by grape respiration and fermentation.
3. The berries change internally. Enzymes inside the living berries drive anaerobic, or oxygen-limited, metabolism.
4. The intracellular phase ends. Alcohol accumulation, pressure, handling and berry condition eventually limit the process.
5. Yeast fermentation takes over or continues. The fruit is crushed or pressed, creating must—the mixture of juice, skins and other grape solids—which can then ferment in a more conventional way.

Strict carbonic maceration requires intact berries with little or no free juice at the start. In commercial winemaking, achieving a completely pure version is difficult because some berries inevitably break. Juice collects at the bottom of the vessel and begins fermenting with yeast, while other intact berries continue their intracellular phase.

Carbonic, semi-carbonic and whole-bunch: what is the difference?

These terms overlap, but they are not interchangeable.

A useful shortcut is this: whole-bunch describes how the fruit is handled; carbonic describes what happens inside intact berries in an oxygen-limited environment.

Extended maceration is different again. It refers to prolonged contact between wine and grape solids, rather than an intracellular phase in intact berries.

What can carbonic maceration do to a wine?

Carbonic maceration can influence several parts of a wine’s profile, but the final result depends on the grape variety, fruit condition, temperature, duration, amount of free juice, stem contact and what happens after the treatment.

Aroma and flavour

Australian Wine Research Institute material associates carbonic techniques with red-berry, cherry or kirsch-like, musk-like, spice, almond and cinnamon-associated aromas. These are possibilities, not a fixed recipe.

The familiar idea that carbonic maceration always produces banana aromas is too simple. A wine’s aroma depends on the whole winemaking pathway, not just the name of the initial treatment.

Acidity and pH

Inside the berries, some malic acid can be metabolised. This may reduce titratable acidity and raise pH, although measured acidity and perceived acidity are not always experienced in the same way. Carbonic maceration should therefore not be treated as a guarantee of a softer-tasting or less acidic wine.

Tannin and texture

Carbonic wines can have softer texture and lower phenolic extraction than conventionally fermented red wines. This is partly because conventional fermentation exposes skins and seeds to wine containing increasing alcohol, which can extract more phenolic material.

However, later skin contact, whole-bunch proportion, pressing and blending can change the result. “Carbonic” does not guarantee low tannin.

Colour and alcohol

The process can alter how colour compounds move from skins into the berry. Final colour may be bright, but it can be higher or lower than a conventionally fermented wine depending on the method and the comparison.

The intracellular phase produces only a small amount of alcohol. Final alcohol is determined mainly by grape sugar and the subsequent yeast fermentation—not by carbonic maceration alone.

Carbonic maceration in Australia

The Australian Wine Research Institute documents carbonic and semi-carbonic techniques in discussions of Gamay, Pinot Noir and Shiraz. It also reports Australian small-lot trials involving Pinot Noir and Shiraz.

That evidence shows the method is part of Australian technical and winemaking discussion. It does not mean carbonic maceration is uniquely Australian, standard across the country or representative of one particular region.

On an Australian wine label or in a tasting note, “carbonic” is best understood as a descriptive claim about how the wine was made. The reviewed Wine Australia guidance does not identify carbonic maceration as a regulated wine style category. As with other production claims, the wording should accurately describe the wine and not mislead.

What should you infer from “carbonic” on a label?

You can reasonably infer that the maker is pointing to a carbonic or partly carbonic treatment. You cannot infer, from that word alone, that the wine is:

• a natural wine;
• organic or biodynamic;
• low in alcohol;
• low in tannin;
• sweet;
• made from a particular grape;
• from a particular Australian region; or
• guaranteed to taste like banana, cherries or bubblegum.

The most useful question is not “What flavour must this have?” but “What might this method have contributed, and what other choices shaped the finished wine?”

Carbonic maceration is one step in a larger process. Understanding that makes wine descriptions easier to read—and helps explain why two wines made with a carbonic technique can still taste quite different.