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. The AWRI describes it as a red winemaking whole bunch fermentation technique in which the first phase of fermentation is conducted in a completely anaerobic atmosphere, and notes that this occurs only if the grapes remain intact with absolutely no free grape juice. The OIV code, which admits the practice under sheet II.1.7, 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. According to the AWRI's 2018 Ask the AWRI column, Michel Flanzy invented the original technique in 1934.

• Michel Flanzy invented the original technique in 1934, per the AWRI's 2018 Ask the AWRI column
• 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 (AWRI)
• 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
• Decanter's Simon Woolf separates whole-bunch fermentation, which simply means not destemming, from carbonic maceration, which specifically refers to anaerobic fermentation of whole bunches

When intact berries absorb carbon dioxide, which fills around 50% of the berry's volume according to the AWRI's 2018 Ask the AWRI column, 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, according to the AWRI. Glycerol and shikimic acid are also produced, and the shikimic acid degrades to cinnamic acids and then to the three main aroma compounds the AWRI associates 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 in the liquid phase. The AWRI says that to complete fermentation the fruit is destemmed, crushed and fermented with yeast under normal winemaking conditions, most commonly off the skins. After a maceration that Inter Beaujolais (2020) puts at 4 to 15 days on average in Beaujolais, the remaining bunches are pressed and the free-run and press juice are blended to continue their fermentation, and for primeur wines INAO's Beaujolais specification says producers want them 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 (AWRI, 2018)
• Intracellular fermentation yields only 0.5-2.2% ethanol (AWRI, 2018); 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 (AWRI, 2018)
• The three main aroma compounds the AWRI links 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 AWRI's 2018 column describes the wines as generally softer and less acidic, with lower extraction of phenolic compounds, and reports that they mature faster than traditionally fermented wines. Decanter says 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. The AWRI suggests that 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, according to Decanter, and under INAO's Beaujolais specification it has been released to consumers on the third Thursday of November since 1985, after a maceration of 4 to 6 days per Inter Beaujolais (2020).

• OIV objective: red or rosé wine that is more supple, less acidic, fresher and with a better expression of varietal aromas
• The AWRI (2018) reports lower extraction of phenolic compounds, and says the technique has historically been recommended for lighter bodied, fruity wines intended for early consumption
• Under INAO's Beaujolais specification, the primeur or nouveau mention is reserved for red and rosé wines, whose cuvaison lasts 10 days or less
• Decanter notes that wines made in this style include Beaujolais Nouveau and are often best when drunk young, sometimes lightly chilled

The AWRI says 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. According to the AWRI, these characters often override any varietal fruit character, but can also add aroma to wines with low varietal or fruit character. Decanter lists bubble gum, kirsch, banana and strawberry among the key flavours, and quotes its tasting notes guide saying that esters such as ethyl cinnamate "are produced in higher quantities than normal, lending flavours such as raspberry, strawberry, and bubblegum." On the palate, Decanter describes the reds as light in colour, low in tannin and soft and fruity.

• Aroma (AWRI): 'strawberry/raspberry' and 'cherry/kirsch', particularly in Beaujolais wines, plus 'vanilla', 'spice', 'almond' and 'cinnamon'
• Key flavours named by Decanter: bubble gum, kirsch, banana and strawberry
• Palate (Decanter): low in tannin with a soft, fruity character
• The AWRI (2018) notes 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

Decanter says carbonic maceration is most commonly associated with the Gamay grape and Beaujolais wines, although not exclusively. INAO's Beaujolais specification says producers habitually practise a typically Beaujolais vinification inspired by semi-carbonic maceration to preserve fruity character, and Inter Beaujolais (2020) calls semi-carbonic maceration a term specific to the region. The AWRI says carbonic and semi-carbonic maceration are commonly applied to Gamay, Pinot Noir and Shiraz, and that the technique has also been used to help decrease naturally high levels of malic acid, or as a blending component. In southern France, JancisRobinson.com says carbonic maceration routinely has to be used so that Carignan, typically high in rough tannins and acidity, can be drunk reasonably young, and the DOCa Rioja Consejo Regulador says Mazuelo, when production is high and the grapes are not yet sufficiently ripe, is best suited to young wines with carbonic maceration.

• Beaujolais: Inter Beaujolais (2020) gives average macerations of 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: INAO dates the official birth of the phenomenon to an administrative note of 13 November 1951, with consumer release on the third Thursday of November from 1985
• Australia: the AWRI (2018) reports winemakers 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, per JancisRobinson.com and the DOCa Rioja Consejo Regulador

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, and the AWRI notes that 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. Inter Beaujolais (2020) describes three layers in the Beaujolais vat: 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, which Inter Beaujolais (2020) calls semi-carbonic maceration, differs in the vat rather than in a stated temperature: 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, the AWRI says more subtle and short-term aromas are produced. The AWRI adds that 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, and within that umbrella Decanter says 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, according to Decanter.

• Full carbonic maceration: 100% intact whole bunches with absolutely no free grape juice in a closed vessel filled with carbon dioxide (AWRI, 2018)
• 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 (Decanter)
• Whole-bunch fermentation: whole bunches, stems and all, go directly into the vat; Decanter says this would have been considered common practice before World War II
• Risks: the AWRI says spoilage by acetic acid bacteria and Brettanomyces yeast is increased 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 2026-09-24