What Is Carbonic Maceration? Learn About the Winemaking Process

Carbonic maceration is a winemaking process that takes place during fermentation to produce fresh, fruit-forward, low-tannin red wines. Carbonic maceration uses whole clusters of grapes in a sealed, carbon dioxide-filled tank to start fermentation within each grape.

Carbonic maceration occurs naturally when whole clusters of grapes ferment in an oxygen-poor (anaerobic) environment, so it may have been a part of winemaking for many years before it was recognized as a distinct process. The French scientist Louis Pasteur was the first to study carbonic maceration’s effect on a wine’s flavor versus regular (aerobic) fermentation. In 1934, Michel Flanzy, another French scientist, noticed the unique effect that carbon dioxide gas had on grapes, especially during fermentation.

Grapes destined for carbonic maceration must be hand harvested in whole bunches rather than destemmed by a machine. The whole grape clusters are added to a fermenting tank that has been flushed with carbon dioxide gas until it displaces all the existing oxygen.

In this anaerobic environment, the grapes release enzymes which cause intracellular fermentation to begin inside the intact berries. Since carbon dioxide is a byproduct of fermentation, the gas continues to build up in the fermenting vessel, contributing to the carbon-dioxide rich environment. The grape skins burst when the juice inside reaches about 2% alcohol.

Winemakers usually separate the juice from the grape skins and stems at this point. They then add selected yeast or let the naturally-occuring yeast on the grape skins begin the yeast fermentation. The fermentation process is complete when the wine is dry, meaning all available sugars from the grape juice have turned into alcohol.

Carbonic maceration creates esters (fruity-smelling chemical compounds) that give certain unmistakable flavors to red wines. These include:

• Bubblegum
• Banana
• Kirsch
• Cinnamon
• Strawberry

Lower tannin and lighter color. Wines made with carbonic maceration are lower in tannin and lighter in color than wines made with a regular fermentation. Tannin and color come from the grape skins, and carbonically macerated wines have a shorter period of skin contact since the grapes remain intact during part of the fermentation.

Reduced acidity. Carbonic maceration also reduces a wine’s acidity. This is because enzymatic fermentation converts some of the tart malic acid in the must into alcohol and other kinds of softer-tasting acids. Malolactic fermentation, the conversion of malic acid into tangy lactic acid, occurs after the primary fermentation and also contributes to a softer mouthfeel.

Red grape varieties that have low tannins are most commonly made with full or semi-carbonic maceration. These include:

• Gamay
• Carignan
• Grenache. Learn more about Grenache in our complete guide here.
• Pinot noir. Learn more about Pinot noir here in our complete guide.
• Syrah. Learn more about Syrah here in our complete guide.
• Tempranillo. Learn more about Tempranillo here in our complete guide.
• Mourvèdre
• Valdiguié (in California)

Carbonic maceration is not used to make white wines. White grape juice is usually pressed off the skins immediately. This is because the skins of white grapes contain tannin, the bitterness of which interferes with the varietal expression of white grapes like sauvignon blanc or riesling.

Semi-carbonic maceration is whole bunch fermentation without the addition of carbon dioxide to the fermenting tank by the winemaker. The weight of the grape clusters crushes the grapes at the bottom of the tank, releasing their juice. The yeast on the grape skins begins fermenting this juice, producing carbon dioxide that creates an anaerobic environment. The whole grapes at the top of the tank then begin enzymatic intracellular fermentation until they burst.

Full carbonic maceration is rarely used except in inexpensive wines produced for immediate consumption following the harvest. Semi-carbonic maceration is used to make fruity wines with some of the aromatics of carbonic maceration but in a more subtle fashion. Semi-carbonic maceration is more common in higher quality Beaujolais wines and sometimes in neighboring Burgundy.

Carbonic maceration should not be confused with cold maceration, a technique used on grapes like cabernet sauvignon and merlot in Bordeaux and California. Pre-fermentation, the grapes macerate at low temperatures for up to five days. This process extracts color and different flavors from the grapes than those that come from the higher temperatures of the fermentation that follows.

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