Carbonic Maceration

How it works

The key is the intact berry. When a whole grape is placed in an oxygen-free environment, the cells inside the skin switch from respiration to fermentation, using the grape's own enzymes to turn a small amount of sugar into alcohol, along with ethanol, glycerol and a range of fruity esters. The berry effectively ferments itself from the inside out. After about a week to ten days, the tank is pressed and the juice, now lightly coloured and intensely aromatic, is run off to finish fermentation in the normal way.

No yeasts are added, no crushing is needed, and the wine has had no skin contact in the conventional sense. The colour comes from pigments that diffuse out through the skin during the intracellular phase, but because the berry has not been broken, tannins and harsh phenolics stay locked in the skins.

Sensory effect

Carbonic maceration wines smell of banana, kirsch, bubblegum and bright red fruit. The palate is soft, low in tannin, juicy and often slightly lower in alcohol. The wines are made to drink young. In Beaujolais, the prime example is Beaujolais Nouveau, released just six to eight weeks after harvest. In other regions, winemakers keep the wine for a few extra months to let the primary fruit settle and the structure firm up.

For red grapes, the technique works best on varieties with thin skins and high sugar, such as Gamay, Pinot Noir and, in the UK, some hybrid reds. For thicker-skinned varieties like Cabernet Sauvignon, the technique is less effective.

Half-carbonic and whole-cluster alternatives

Many modern winemakers use a half-carbonic approach, where part of the tank is filled with whole clusters and part with crushed grapes. The crushed portion ferments normally and produces a steady stream of CO2 that helps maintain the anaerobic environment for the whole clusters. The finished wine is a hybrid that combines the fruit of carbonic with the structure of a conventional fermentation.

Whole-cluster fermentation, where uncrushed bunches are dropped into a tank and allowed to start fermenting under their own weight, is a related but distinct technique. It produces wines with more tannin and complexity than pure carbonic maceration. In the UK, the technique is sometimes called "whole bunch" and is most often used for premium Pinot Noir.

Carbonic maceration in the UK

UK interest in carbonic maceration has been growing. A handful of producers, including Ancre Hill, Gusbourne's experimental "White" Pinot project, Offbeat in Hackney, Tuffnell's, and Forest Gin and Wine in the West Country, have made carbonic Pinot Noir or Pinot Noir Précoce releases. The UK climate suits the technique because Pinot Noir already has the right aromatic profile, and the lower tannin extraction suits the sometimes under-ripe skins of cool vintages.

The wines are typically released in spring, marketed as fresh, juicy, light reds to be chilled and drunk young. Some producers have started making carbonic rosé by using the technique on Pinot Noir picked early for sparkling base wine, then pressing the lightly tinted juice off the skins after the intracellular phase.

Limits and considerations

Carbonic maceration is hard work. Loading a tank with whole bunches without breaking any of them is labour-intensive, and the tank must be sealed carefully. The risk of stuck fermentation is higher than in conventional red winemaking because the intracellular phase is unpredictable. And the resulting wine is fragile, with low tannin and low sulphur dioxide tolerance, so it does not age well.

For these reasons, carbonic wines are a small, fun part of the UK wine map, not a foundation. Most UK producers still prefer the conventional approach for their main Pinot Noir cuvée, and use carbonic only as a side project to add diversity to the range and to capture the fruit-forward style that some consumers want.