Intracellular Fermentation: Carbonic Maceration

Carbonic maceration is a winemaking process in which whole, uncrushed grape clusters are placed in a sealed vessel filled with carbon dioxide, allowing individual berries to undergo intracellular fermentation through their own enzymatic activity before any yeast involvement. It is a red winemaking whole bunch fermentation technique in which the first phase of fermentation is conducted in a completely anaerobic atmosphere, and this occurs only if the grapes remain intact with absolutely no free grape juice. The OIV code admits the practice under sheet II.1.7 and specifies a closed tank whose carbon dioxide comes from an external source, from the respiration of the grapes and the fermentation of part of the crushed berries, or from both. Michel Flanzy invented the original technique in 1934.

• Origin: Michel Flanzy invented the original technique in 1934
• Stephen Hickinbotham patented a modified version in 1986 in which whole bunches go into a plastic bag supported by a pallet box, with a small quantity of dry ice in an insulated container, the bag sometimes fitted with a one-way valve
• The OIV's general maceration sheet (II.1.16) lists carbonic maceration among its maceration techniques, alongside traditional fermentation on skins and prefermentative cold maceration
• Whole-bunch fermentation simply means not destemming, while carbonic maceration specifically refers to anaerobic fermentation of whole bunches

When intact berries absorb carbon dioxide, which fills around 50% of the berry's volume, they shift from a respiratory to an anaerobic metabolism. Within the berry, grape alcohol dehydrogenase transforms sugar into ethanol and carbon dioxide, while the enzyme malic dehydrogenase metabolises malic acid into ethanol, succinic acid and aminobutyric acid without producing any lactic acid. Glycerol and shikimic acid are also produced, and the shikimic acid degrades to cinnamic acids and then to the three main aroma compounds associated with carbonic maceration. In semi-carbonic maceration, grapes at the bottom of the tank are crushed by weight, releasing juice that undergoes conventional yeast fermentation. To complete fermentation, the fruit is destemmed, crushed and fermented with yeast under normal winemaking conditions, most commonly off the skins. In Beaujolais, after a maceration of 4 to 15 days on average, the remaining bunches are pressed and the free-run and press juice are blended to continue their fermentation; primeur wines are made to be ready quickly, with malolactic fermentation finished.

• Carbon dioxide absorbed by the berry fills around 50% of its volume, and the berry shifts from a respiratory to an anaerobic metabolism
• Intracellular fermentation yields only 0.5-2.2% ethanol; a subsequent conventional yeast fermentation is required to complete the wine
• Malic dehydrogenase lowers titratable acidity and raises pH by metabolising malic acid, with no lactic acid produced
• The three main aroma compounds linked to carbonic maceration are benzaldehyde ('cherry', 'kirsch', 'almond'), vinylbenzene ('styrene', 'plastic') and ethyl cinnamate ('cinnamon', 'strawberry', 'honey')

The OIV gives the objective of carbonic maceration as red or rosé wine that is more supple, less acidic, fresher and with a better expression of varietal aromas. The wines are generally softer and less acidic, with lower extraction of phenolic compounds, and they are thought to mature faster than traditionally fermented wines. The method extracts some colour from the grapes but little tannin, generally creating red wines that are light in colour, low in tannin and soft and fruity. Tannin extracted into the pulp at low alcohol is more likely to be skin tannin than seed tannin, which could lead to a perception of softer tannin. Beaujolais Nouveau is one of the wines made in this style; since 1985 it has been released to consumers on the third Thursday of November, after a maceration of 4 to 6 days.

• OIV objective: red or rosé wine that is more supple, less acidic, fresher and with a better expression of varietal aromas
• Lower extraction of phenolic compounds; the technique has historically been recommended for lighter bodied, fruity wines intended for early consumption
• Under the Beaujolais appellation rules, the primeur or nouveau mention is reserved for red and rosé wines, whose cuvaison lasts 10 days or less
• Wines made in this style include Beaujolais Nouveau and are often best when drunk young, sometimes lightly chilled

Carbonic maceration wines have a distinctive aroma which often polarises tasters, described as 'fruity' or 'musk-like', with 'strawberry/raspberry' and 'cherry/kirsch' aromas, particularly in Beaujolais wines, but also 'vanilla', 'spice', 'almond', 'cinnamon', 'sandalwood' or 'oak-like' characters. These characters often override any varietal fruit character, but can also add aroma to wines with low varietal or fruit character. Key flavours include bubble gum, kirsch, banana and strawberry. In the words of Decanter's tasting notes guide, esters such as ethyl cinnamate "are produced in higher quantities than normal, lending flavours such as raspberry, strawberry, and bubblegum." On the palate, the reds are light in colour, low in tannin and soft and fruity.

• Aroma: 'strawberry/raspberry' and 'cherry/kirsch', particularly in Beaujolais wines, plus 'vanilla', 'spice', 'almond' and 'cinnamon'
• Key flavours: bubble gum, kirsch, banana and strawberry
• Palate: low in tannin with a soft, fruity character
• The wines often show lower primary fruit flavours, possibly because some common wine esters such as hexyl acetate form only in an oxygen-rich environment

Carbonic maceration is most commonly associated with the Gamay grape and Beaujolais wines, although not exclusively. To preserve fruity character, Beaujolais producers habitually practise a typically Beaujolais vinification inspired by semi-carbonic maceration, a term specific to the region. Carbonic and semi-carbonic maceration are commonly applied to Gamay, Pinot Noir and Shiraz, and the technique has also been used to help decrease naturally high levels of malic acid, or as a blending component. In southern France, carbonic maceration routinely has to be used so that Carignan, typically high in rough tannins and acidity, can be drunk reasonably young. In Rioja, Mazuelo is best suited to young wines with carbonic maceration when production is high and the grapes are not yet sufficiently ripe.

• Beaujolais: average macerations run around 10 to 15 days for the ten crus, around 6 to 10 days for Beaujolais and Beaujolais Villages, and 4 to 6 days for primeur wines
• Beaujolais Nouveau: the phenomenon was officially born with an administrative note of 13 November 1951, with consumer release on the third Thursday of November from 1985
• Australia: winemakers are experimenting with carbonic maceration or partial whole bunch ferments in Pinot Noir and Shiraz to produce more elegant and perfumed wines
• Southern France and Rioja: Carignan, known in Rioja as Mazuelo

For full carbonic maceration, intact whole bunches are placed in a closed fermentation vessel and an anaerobic atmosphere is created, generally by using carbon dioxide to exclude oxygen, though under commercial winemaking conditions it is almost impossible to produce a wine that depends wholly on carbonic maceration for the first phase of fermentation. The more common semi-carbonic maceration relies on whole clusters placed in a vat that is not hermetically sealed; grapes at the bottom are crushed by the weight of those above, and the CO₂ released by their yeast fermentation kick-starts carbonic maceration in the intact berries above. A Beaujolais vat has three layers: whole bunches at the top undergo intracellular fermentation as carbonic gas progressively replaces the oxygen, bunches in the middle macerate in the accumulating juice, and compressed grapes at the bottom release juice that yeasts ferment. Traditional Beaujolais practice is semi-carbonic maceration: the vat is not hermetically sealed, no carbonic gas is added, and maceration runs around 10 to 15 days for the crus. At lower temperatures, over a longer maceration period of up to three weeks, more subtle and short-term aromas are produced. Including a percentage of whole bunches or whole berries with crushed grapes results in some carbonic maceration within the whole berries, but with lesser amounts of the distinctive flavours. As a broader umbrella, the OIV's general maceration sheet (II.1.16) lists carbonic maceration as one of several maceration techniques, alongside traditional fermentation on skins and prefermentative cold maceration; within that umbrella, carbonic maceration specifically refers to anaerobic fermentation (without the presence of oxygen) of whole bunches. Whole-bunch fermentation, by contrast, simply refers to the practice of not destemming grapes.

• Full carbonic maceration: 100% intact whole bunches with absolutely no free grape juice in a closed vessel filled with carbon dioxide
• Semi-carbonic maceration: no added carbon dioxide; yeast ferments the juice of the crushed lower grapes and releases CO₂, kick-starting carbonic maceration in the un-burst grapes
• Whole-bunch fermentation: whole bunches, stems and all, go directly into the vat, a practice that would have been considered common before World War II
• Risks: spoilage by acetic acid bacteria and Brettanomyces yeast increases during carbonic maceration because of the higher pH, higher temperatures and absence of sulfur dioxide

Primary sources (OIV, AWRI, Inter Beaujolais, INAO, DOCa Rioja Consejo Regulador): https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/grapes/carbonic-maceration, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-carbonic-maceration/, https://www.awri.com.au/wp-content/uploads/2018/05/s2005.pdf, https://www.beaujolais.com/en/2020/09/22/beaujolais-vinification-a-process-like-no-other/, https://extranet.inao.gouv.fr/fichier/PNO-cdcBeaujolais-cn220210.pdf, https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/grapes/maceration-%28general-sheet%29, https://riojawine.com/en-us/the-designation/grape-varieties/mazuelo/. Secondary sources: https://www.decanter.com/learn/advice/carbonic-maceration-54082/, https://www.decanter.com/learn/advice/what-is-whole-bunch-fermentation-ask-decanter-353983/, https://www.jancisrobinson.com/learn/grape-varieties/red/carignan. Last verified 2026-10-05