Intracellular Fermentation — Carbonic Maceration

Carbonic maceration is a winemaking process in which whole, uncrushed grape clusters are placed in a sealed vessel saturated with carbon dioxide, allowing individual berries to undergo intracellular fermentation through their own enzymatic activity before any yeast involvement. The technique was invented by the French scientist Michel Flanzy (1902–1992) in 1934, when experiments on preserving dessert grapes in a CO₂-rich atmosphere in the Narbonne district unexpectedly produced wines of distinctive and appealing character. Although some of the earliest scientific observations of the underlying phenomenon were recorded by Louis Pasteur in 1872, Flanzy was the first to document and systematically develop it as a deliberate winemaking method. The technique gained broader application in Beaujolais from the 1960s onward, with figures such as négociant and chemist Jules Chauvet contributing to its study and spread.

• First experiments conducted in 1934 in the Narbonne district; Flanzy originally intended to preserve table grapes, not make wine
• Louis Pasteur noted in 1872 that grapes kept in CO₂-rich environments produced wines of different flavor from those fermented conventionally
• Jules Chauvet, a négociant and chemist from Beaujolais, made important contributions to the study of semi-carbonic maceration in the mid-20th century
• CM is distinct from whole-bunch fermentation used in Burgundy; the latter does not require a sealed anaerobic tank and involves stems throughout

When intact grape berries are exposed to a CO₂-rich anaerobic atmosphere, they rapidly shift from aerobic respiration to fermentative anaerobic metabolism. The key enzyme system is grape alcohol dehydrogenase (VvADH), which transforms sugars and malic acid into ethanol and CO₂ from within the berry. This intracellular fermentation produces only around 1.5–2% alcohol, alongside secondary by-products including glycerol, acetaldehyde, and various esters that define the aromatic signature of the style. Malic acid is reduced by roughly half during this phase. Simultaneously, grapes at the bottom of the tank are crushed by weight, releasing juice that undergoes conventional yeast fermentation in the liquid phase. After 5–15 days, the intact berries are pressed and the remaining must completes fermentation with yeast, followed by malolactic fermentation.

• Grape alcohol dehydrogenase (VvADH) is the primary enzyme driving intracellular sugar and malic acid conversion to ethanol under anaerobic conditions
• Intracellular fermentation yields only 1.5–2% ABV; a subsequent conventional yeast fermentation is always required to complete the wine
• Malic acid is reduced by approximately half enzymatically, lowering acidity and raising pH without bacterial intervention
• Secondary metabolites including volatile esters, shikimic acid derivatives, and glycerol contribute the characteristic aromatic signature of banana, cherry, cinnamon, and almond

Carbonic maceration fundamentally reshapes a wine's aromatic and structural profile by prioritizing fruit expression and textural softness over tannin grip and aging potential. The resulting wines are lighter in color, lower in titratable acidity, higher in pH, and markedly softer on the palate than conventionally made reds from the same grape. Beaujolais Nouveau is the most globally recognizable expression, bottled just six to eight weeks after harvest and released on the third Thursday of November. Beyond Nouveau, the technique in its semi-carbonic form is used across all Beaujolais appellations and crus to varying degrees, and it is applied to tannic varieties like Carignan in the Languedoc and Rhône to deliver rounder, more approachable blending components.

• Wines show lighter color, softer tannins, higher pH, and lower titratable acidity compared to conventionally fermented reds from the same variety
• Aromatic profile features red fruits (strawberry, cherry, raspberry), stone fruit, and distinctive fermentation notes of banana, bubblegum, almond, cinnamon, and kirsch
• Beaujolais Nouveau, bottled 6–8 weeks after harvest, is the most extreme and commercially prominent CM expression, released each third Thursday of November
• Best consumed young; basic Beaujolais and Nouveau are intended for drinking within one year, while premium Beaujolais crus can develop for several years

Carbonic maceration wines carry a recognizable aromatic fingerprint even before the first sip. On the nose, expect vivid red fruit, fresh cherry, strawberry, and distinctive secondary notes derived from shikimic acid metabolism: benzaldehyde (almond), ethyl cinnamate (cinnamon), and esters (banana, bubblegum). These aromatic compounds often override varietal character entirely in lighter CM examples but can complement or add complexity in varieties with lower native fruit expression. On the palate, the wines are light- to medium-bodied with silky texture, low astringency, bright acidity, and a relatively short to medium finish. Color tends to be translucent ruby or garnet. The absence of oak influence is common, as these wines are designed for early drinking without barrel aging.

• Nose: red berries, fresh cherry, strawberry, and characteristic CM esters including almond, cinnamon, banana, and bubblegum
• Palate: silky and low-tannin with soft acidity, light to medium body, and a clean, fruit-forward finish
• Color is typically lighter and less saturated than traditionally macerated reds; translucent ruby or garnet hues are hallmarks
• Aromas are most vibrant in the months immediately after release and diminish over 1–2 years, making these wines best consumed young

Beaujolais is the global heartland of carbonic maceration, with négociants Georges Duboeuf, Louis Jadot, and Mommessin among the best-known commercial producers of Beaujolais Nouveau. In practice, most Beaujolais producers — including estate growers across the ten crus (Morgon, Fleurie, Moulin-à-Vent, Brouilly, Côte de Brouilly, Régnié, Chiroubles, Chénas, Juliénas, and Saint-Amour) — use a semi-carbonic approach rather than full CM, relying on whole clusters without added CO₂. Beyond Beaujolais, CM and semi-CM are applied to Carignan in the Languedoc and Rhône for use as a blending component, and to wines in Rioja Alavesa and Jumilla in Spain. In California, Valdiguié is sometimes vinified by CM to produce a Nouveau-style wine, and New World producers increasingly apply the technique to Gamay, Pinot Noir, and Shiraz.

• Beaujolais Nouveau: Georges Duboeuf, Louis Jadot, and Mommessin are among the most prominent commercial producers of the primeur style
• The ten Beaujolais crus (including Morgon, Fleurie, and Moulin-à-Vent) typically use a semi-carbonic method with whole clusters and no added CO₂
• Spain: Rioja Alavesa and Jumilla are the two regions most closely associated with CM outside France
• New World applications include California Valdiguié Nouveau, and increasing use with Gamay, Pinot Noir, and Shiraz in Australia and New Zealand

Full carbonic maceration, in which CO₂ is actively pumped into a sealed tank before vatting, is technically demanding and relatively rare even in Beaujolais. The more commonly practiced semi-carbonic maceration relies on whole clusters piled into an unsealed or loosely sealed vessel; grapes at the bottom are crushed by gravity, and the CO₂ released by their yeast fermentation creates an anaerobic atmosphere for the intact berries above. This is the standard method across most Beaujolais appellations. Anaerobic maceration is a broader umbrella term that includes CM variants and CO₂-saturated fermentations to which exogenous yeast may be added. Cold soak is a different, lower-temperature technique used before conventional fermentation to extract color and aroma without tannins. Whole-bunch fermentation, common in Burgundy, is distinct: it involves uncrushed clusters with stems in an open vessel without a deliberate CO₂ atmosphere.

• Full CM requires active CO₂ injection into a sealed tank before vatting; it is technically demanding and rarely achieved in pure form commercially
• Semi-carbonic maceration, the standard Beaujolais method, relies on natural CO₂ from crushed bottom-layer grapes to create anaerobic conditions for intact berries above
• Whole-bunch fermentation, associated with Burgundy Pinot Noir, is distinct: it uses no sealed CO₂ environment and the stems play a structural, not anaerobic, role
• Cold soak, conducted at 4–10°C before fermentation, extracts color and fruit aromatics differently from CM and does not involve intracellular fermentation