Semi-Carbonic Maceration

Semi-carbonic maceration is a whole-bunch fermentation method in which grapes are loaded intact into a vessel without the addition of external carbon dioxide. The weight of the grapes on top crushes the ones below, releasing juice; yeast ferments that juice and releases CO₂, kick-starting carbonic maceration in the grapes that remain unburst. The OIV International Code of Oenological Practices (sheet II.1.7) defines carbonic maceration broadly enough to include this approach: whole grapes are placed for a few days in 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. In Beaujolais, producers customarily practise a typically Beaujolais vinification inspired by semi-carbonic maceration in order to preserve fruity character. Michel Flanzy invented the original carbonic maceration technique in 1934.

• Distinct from full carbonic maceration, which places 100% intact whole bunches, with absolutely no free grape juice, in a closed vessel filled with carbon dioxide; semi-carbonic maceration relies on the CO₂ released by fermentation of the crushed grapes
• Jules Chauvet (1907-1989), a Beaujolais négociant, chemist and author, earned the title 'the father of natural wine' for his scientific research into the action of yeast and the carbonic maceration technique
• Semi-carbonic maceration is one of several whole-bunch fermentation techniques that produce some carbonic maceration within the whole berries, alongside ferments that include a percentage of whole bunches or whole berries with crushed grapes

The process unfolds in two stages within the same vessel. At the bottom, the crushed grapes undergo conventional fermentation: yeast ferments the juice and releases carbon dioxide. That CO₂ creates an anaerobic atmosphere for the intact clusters above; the Beaujolais method relies on the CO₂ produced naturally by the ferment. Inside each whole berry, an intracellular, enzyme-driven fermentation begins without yeast intervention: sugars are converted to only 0.5-2.2% alcohol, malic acid is broken down, and distinctive aromatic compounds accumulate. Carbon dioxide absorbed by the berries fills around 50% of their volume and shifts their metabolism from respiration to anaerobic metabolism. Research by Etaio and colleagues (2008) suggests that anthocyanins diffuse from the skin into the pulp, and that any tannin extracted at low alcohol is more likely skin tannin than seed tannin, which could lead to a perception of softer tannin. As the whole berries burst, they release juice and are pressed under their own weight.

• Benzaldehyde (cherry, kirsch, almond), vinylbenzene (styrene, plastic) and ethyl cinnamate (cinnamon, strawberry, honey) are the three main aroma compounds associated with carbonic maceration
• The enzyme malic dehydrogenase converts malic acid into ethanol, succinic acid and aminobutyric acid without producing lactic acid, which decreases titratable acidity and increases pH
• Glycerol and shikimic acid are also produced inside the berry
• Carbonic maceration character and structure occur best when grapes are kept around 30-32 °C for five to eight days

Carbonic maceration aromas tend toward the fruity or musk-like, with strawberry, raspberry, cherry and kirsch notes (particularly in Beaujolais wines) and sometimes vanilla, spice, almond or cinnamon characters; these characters often override varietal fruit character. Bubble gum, kirsch, banana and strawberry are key flavours associated with the technique. The OIV code 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 carbonic and semi-carbonic maceration process extracts colour but not tannin, giving a light, soft, juicy wine with kirsch and bubblegum aromas for early drinking. Semi-carbonic maceration yields lesser amounts of the distinctive carbonic flavours than full carbonic maceration.

• Aromas: strawberry, raspberry, cherry and kirsch, with bubble gum and banana also associated with the style
• Structure: generally softer and less acidic, with lower extraction of phenolic compounds, and thought to mature faster than traditionally fermented wines
• Contrast: after the AWRI made small-lot Pinot Noir and Shiraz wines in the 2016 and 2017 vintages, winemakers asked why wines made with 100% pure carbonic maceration differed so much in sensory terms from those made with the more common semi-carbonic maceration or whole-bunch treatments

The AOC Beaujolais specification ties semi-carbonic maceration to the region: producers customarily practise a typically Beaujolais vinification inspired by semi-carbonic maceration to preserve fruity character. The same rules cap the vatting time of primeur or nouveau wines at 10 days or less; primeur producers practise shorter macerations, and vatting for wines intended for ageing is generally longer, to develop aromatic complexity and tannic structure. 'Beaujolais can certainly claim to be the spiritual home of whole-bunch fermentation,' wrote Simon Woolf in the February 2017 issue of Decanter. Jules Chauvet gathered disciples including Marcel Lapierre, Jean Foillard, Jean-Paul Thévenet and Guy Breton, based in and around Morgon, whom their American importer Kermit Lynch called the 'Gang of Four'. The four favoured Chauvet's carbonic maceration, with whole clusters in a sealed tank covered with carbon dioxide, while some other Morgon winemakers use whole clusters without sealing the tank, which is semi-carbonic maceration.

• Marcel Lapierre decided to vinify without sulphur under the influence of Jules Chauvet, and the domaine's wines are made using classic carbonic maceration of nine to 35 days, depending on the cuvée
• Carbonic and semi-carbonic maceration are commonly applied to Gamay, Pinot Noir and Shiraz for light-bodied, brightly coloured wines intended for early consumption, and have also been used to reduce naturally high malic acid or to make a blending component
• Pinot growers in Australia and Burgundy also ferment at least a portion of their vintage using whole bunches

Grape integrity matters: full carbonic maceration occurs only if the grapes remain intact with absolutely no free grape juice. Hand harvesting is required because whole bunches are needed for carbonic and semi-carbonic maceration. Risks of spoilage by acetic acid bacteria and Brettanomyces yeast are increased during carbonic maceration due to the higher pH, elevated temperatures and absence of sulfur dioxide, and aerobic microorganisms can quickly take over if a carbon-dioxide-rich environment is not adequately maintained. Under commercial winemaking conditions, it is almost impossible to produce a wine that depends wholly on carbonic maceration for the first phase of fermentation. Timing of pressing is tied to the intracellular phase: once it is completed, the grapes are pressed off the skins and yeast completes the fermentation.

• Spoilage risk: acetic acid bacteria and Brettanomyces, driven by higher pH, elevated temperatures and the absence of sulfur dioxide
• Harvest: AOC Beaujolais rules make sorting compulsory, in the vineyard or the cellar, and set rules for machine-harvested plots destined for red or rosé wines, including a maximum depth of 0.50 metre of grapes in transport containers
• Venting: the OIV code requires a device for venting the gas so that the internal pressure does not exceed atmospheric pressure

Semi-carbonic maceration sits between two related practices. Full carbonic maceration places intact whole bunches in a closed vessel with an anaerobic atmosphere, generally obtained by using carbon dioxide to exclude oxygen; a modified version patented by Stephen Hickinbotham in 1986 seals whole bunches in a plastic bag in a pallet box with a small quantity of dry ice. Whole-bunch (whole-cluster) fermentation simply means not destemming: whole bunches, stems and all, go directly into the fermentation vat, a practice that would have been considered common before World War II. After carbonic maceration, the OIV code prescribes that the grapes are crushed and pressed and the separated must is fermented in the absence of solid matter.

• Full carbonic maceration: 100% intact whole bunches, no free juice, closed vessel filled with carbon dioxide
• Whole-bunch fermentation: stems retained; ferments with a percentage of whole bunches are among the techniques that give some carbonic maceration within the whole berries
• The WSET Level 4 Diploma specification (August 2025) lists carbonic maceration and semi-carbonic maceration under whole berry/bunch fermentation

Primary sources (OIV, AWRI, INAO and WSET): 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/s2005/, https://extranet.inao.gouv.fr/fichier/PNO-cdcBeaujolais-cn220210.pdf, https://www.wsetglobal.com/media/17609/wset_l4wines_specification_en_august-2025.pdf, https://www.wsetglobal.com/media/6715/wset_l4diploma_cag_theory_en_aug2018.pdf. 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.decanter.com/premium/marvellous-morgon-a-guide-to-this-star-beaujolais-cru-535143/. The INAO AOC Beaujolais text is the national-opposition version of 10 February 2022. Last verified 2026-10-05