Techniques that shape a wine

Carbonic maceration

Carbonic maceration is a fermentation method that turns red grapes into wines that are light in colour, low in tannin and packed with bright, juicy fruit. It is most famous in Beaujolais, but the technique is used across France and the world whenever a winemaker wants freshness over structure.

What happens inside the tank

Instead of crushing the grapes and letting yeast ferment the juice, whole, unbroken bunches are placed in a sealed tank. Carbon dioxide is added — or builds naturally as grapes at the bottom are gently crushed by the weight of those above — and the tank fills with CO₂. The lack of oxygen changes everything.

Inside each intact berry, a form of fermentation begins without yeast. The grape uses its own enzymes to convert a small amount of its sugar into alcohol and aromatic compounds. This is called intracellular or whole-berry fermentation. It produces distinctive flavours: kirsch, bubblegum, strawberry, banana and violet.

Two fermentations at once

A carbonic-maceration tank usually contains two zones. At the bottom, grapes burst under pressure and release juice. Yeast ferments this free juice in the normal way, creating heat and more CO₂. At the top, the whole berries sit in the CO₂-rich atmosphere and undergo enzymatic fermentation inside their skins.

When the tank is opened, the intact grapes are pressed. Their juice is then often blended back with the already-fermented wine from below. Because the berries spent little time with their skins, colour and tannin extraction are gentle, giving a supple, approachable wine.

Why the wine tastes so fruity

Carbonic maceration favours the formation of esters and higher alcohols that smell candied and perfumed. Malic acid is preserved, keeping the wine crisp. Tannins stay low because the skins and seeds are not worked aggressively. The result is a wine that is vivid, gulpable and best served slightly chilled.

Where you find it in France

• Beaujolais — the classic home of carbonic maceration, especially in Beaujolais Nouveau and many cru Beaujolais from villages like Fleurie, Morgon and Chiroubles.
• Languedoc and Rhône — some producers use a portion of whole bunches to add perfume and freshness to Grenache and Syrah blends.
• Loire — natural winemakers in Touraine and Anjou often employ carbonic or semi-carbonic methods on Gamay and Cabernet Franc.

Carbonic vs. whole-cluster

Carbonic maceration is not the same as whole-cluster fermentation. Whole-cluster fermentation simply means grapes are fermented with their stems; they may still be crushed and yeast-fermented normally. Carbonic maceration specifically relies on intact berries in a CO₂-filled environment. Many wines, including some Burgundies and northern Rhône Syrahs, use a little whole-cluster character without going fully carbonic.

Semi-carbonic maceration

Semi-carbonic maceration sits between full carbonic maceration and a conventional crush-and-yeast fermentation. It is the practical compromise most often used in Beaujolais crus and in many Loire and Languedoc cellars: enough whole-bunch fruit to gain perfume and suppleness, but enough crushed fruit to give the wine structure, colour and a sense of place.

How the tank is loaded

Instead of filling the tank with intact bunches and sealing it tight, the winemaker layers whole, uncrushed bunches at the bottom of the vessel and adds a cap of whole bunches on top. The weight of the upper layers crushes some of the fruit below, releasing juice. That juice begins a normal yeast fermentation, producing alcohol, heat and carbon dioxide.

The CO₂ rises through the tank and saturates the upper layer of intact berries. Those berries then undergo partial intracellular fermentation, just as they would in full carbonic maceration, but for a shorter time and in a less controlled atmosphere. When the cap is pressed, the carbonic portion is blended with the conventionally fermented juice below.

What changes in the glass

The result is a wine with the lifted, red-fruit perfume of carbonic maceration — strawberry, cherry, violet and sometimes a touch of kirsch — but with more tannin, deeper colour and a firmer finish than a fully carbonic wine. The crushed fruit contributes phenolics and structure; the whole-bunch fruit contributes aromatic esters and a supple texture.

Because the fermentation is partly conventional, semi-carbonic wines usually carry more alcohol and weight than their fully carbonic counterparts. They can also age longer. A Morgon or Moulin-à-Vent made with semi-carbonic methods can develop for five to ten years, where a Beaujolais Nouveau is made to be drunk within months.

Where it appears in France

• Beaujolais crus — Fleurie, Morgon, Moulin-à-Vent and Juliénas often use semi-carbonic maceration to balance the region's Gamay fruit with the density and ageing potential expected of a cru wine.
• The Loire — Gamay from Touraine and Cabernet Franc from Anjou are frequently handled with a short semi-carbonic period to add fragrance without losing freshness.
• Languedoc and Roussillon — some Carignan, Grenache and Syrah blends see a portion of whole bunches for a semi-carbonic effect, giving lift to warm-climate fruit.

Semi-carbonic vs. carbonic vs. whole-cluster

Full carbonic maceration relies on intact berries in a sealed, CO₂-rich tank from start to finish. Semi-carbonic allows some berries to be crushed and ferment normally, so the wine keeps more structure. Whole-cluster fermentation, by contrast, simply means the stems remain attached during fermentation; it may be fully conventional, fully carbonic, or semi-carbonic. The three terms describe different decisions — berry integrity, stem inclusion and tank atmosphere — and winemakers often combine them.

Malolactic fermentation

Malolactic fermentation is the bacterial conversion of malic acid — the sharp, green-apple acid found in grapes — into lactic acid, the softer, milky acid found in yoghurt. Despite the name, it is not a true fermentation; no sugar is consumed. It is a transformation of acidity, and it has a profound effect on the texture and stability of a wine.

The bacteria behind the change

The work is done mostly by Oenococcus oeni, a lactic acid bacterium that thrives in wine after alcoholic fermentation. Other genera such as Lactobacillus and Pediococcus can also perform the conversion, but O. oeni is the winemaker's preferred partner because it tolerates alcohol and low pH better than most.

The bacteria do not need oxygen, but they do need a few conditions to succeed: the alcoholic fermentation must be largely finished, the pH must not be too low, the temperature must be warm enough (usually around 18–22 °C), and the wine must have some residual nutrients. Winemakers can either wait for the bacteria to arrive naturally from the cellar, or they can inoculate with a selected strain.

What malolactic fermentation changes

The most obvious change is in the mouth. Malic acid is tart and angular; lactic acid is rounder and creamier. A wine that has completed malolactic fermentation therefore feels less aggressive, with a softer finish and a broader mid-palate. The total acidity drops only slightly, but the perceived acidity changes dramatically.

At the same time, the bacteria produce small amounts of flavour compounds. Diacetyl gives the buttery, creamy note often associated with barrel-fermented Chardonnay. Other by-products contribute to texture and complexity, including a slight increase in mouthfeel.

Why winemakers want it

• Stability — once malic acid is converted, the wine is no longer a favourable environment for spoilage bacteria that could later turn malic acid into unwanted compounds.
• Texture — the wine becomes smoother and more approachable, especially important in reds with firm tannins.
• Complexity — the creamy, dairy-like notes add another layer to both white and red wines.
• Balance — in cool vintages or high-acid regions, malolactic fermentation can prevent the wine from tasting too sharp.

Where it is encouraged — and where it is blocked

In France, almost every red wine is allowed, even expected, to go through malolactic fermentation. Bordeaux, Burgundy, the Rhône and the Loire all rely on it to soften tannins and integrate oak. In Champagne, malolactic fermentation is standard for most non-vintage cuvées, giving the wines their signature creamy texture.

For white wines, the decision is more stylistic. A rich Meursault or Puligny-Montrachet will usually complete malolactic fermentation to match the wine's weight with creamy acidity. A crisp Sancerre, Muscadet or Alsace Riesling, on the other hand, is often protected from it so that the green-apple snap of malic acid remains. Sulphur dioxide and cool temperatures are the winemaker's main tools for blocking it.

Timing matters

Traditionally, malolactic fermentation happens after the yeast have finished turning sugar into alcohol. Today, many winemakers encourage co-inoculation, where the bacteria are added while the alcoholic fermentation is still active. This can speed up the process and reduce the risk of spoilage organisms colonising the wine during the vulnerable gap between the two fermentations.

In barrel-aged wines, malolactic fermentation often takes place in barrel. The gentle oxygen exchange through the wood helps the bacteria and can knit the wine's components together earlier. In tank-aged whites, it may happen in stainless steel, preserving freshness while still rounding the acidity.

Lees ageing

Lees ageing is the practice of leaving a wine in contact with the fine sediment that settles after fermentation — the dead yeast cells, grape skins fragments, tartrate crystals and other microscopic matter known collectively as the lees. What sounds unappealing is in fact one of the most useful tools a winemaker has for building texture, complexity and stability.

What the lees contain

After yeast convert sugar into alcohol, the cells die and sink to the bottom of the tank or barrel. These spent cells are rich in proteins, lipids, mannoproteins and polysaccharides. As they slowly break down, they release compounds that interact with the wine, changing its mouthfeel, aroma and resistance to oxidation.

Sur lie and bâtonnage

Sur lie simply means "on the lees". In its simplest form the wine rests undisturbed, gaining a subtle, savoury depth. In many white wines, especially those aged in barrel, the winemaker will practise bâtonnage — stirring the lees back into suspension with a long baton. This increases contact between the wine and the lees, speeds up the release of mannoproteins and can make the wine feel richer and more rounded.

What lees ageing changes

• Texture — the wine gains weight and a silky, almost creamy mouthfeel. This is especially valuable in whites that might otherwise feel thin or sharp.
• Flavour — lees can add notes of bread dough, biscuit, brioche, hazelnut and sometimes a subtle saline or savoury quality.
• Stability — compounds released by the lees bind with oxygen and can reduce the risk of oxidation, helping the wine age more gracefully.
• Integration — lees ageing can soften oak influence and help knit together fruit, acidity and tannin.

Where you find it in France

• Muscadet — the classic French example. Sur-lie ageing is so central to the style that "Muscadet-sur-Lie" is its own appellation, giving the wine a faintly yeasty, saline character.
• Burgundy — white Burgundy from Meursault, Puligny-Montrachet and Chassagne-Montrachet is often aged on lees in barrel with regular bâtonnage, contributing to its signature richness.
• Champagne — the extended ageing of Champagne on its lees after the second fermentation is what creates the autolytic flavours of toast, pastry and nuts.
• The Rhône and Languedoc — some white and even red wines are aged on lees to add savoury complexity and polish to warm-climate fruit.

The risk of reduction

Lees ageing is not without hazards. If the lees are left too long in a sealed vessel without enough oxygen, the wine can become reduced, developing unpleasant smells of rotten egg, rubber or struck match. Winemakers manage this by allowing tiny amounts of oxygen to reach the wine — through barrel staves, careful topping-up, or controlled micro-oxygenation — and by monitoring sulphur levels closely.

Fining

Fining is the process of adding a clarifying agent to a wine so that suspended particles — proteins, tannins, phenolic compounds, dead yeast cells and other microscopic matter — bind together and settle out. The goal is not to strip the wine of character, but to polish it: improving clarity, reducing bitterness or astringency, and helping the wine remain stable in bottle.

How fining works

A fining agent is mixed into the wine and left to interact for a period of hours, days or weeks. Depending on the agent, it may attract oppositely charged particles, form electrostatic bonds, or simply absorb unwanted compounds. Once the agent has done its work, it settles to the bottom of the tank or barrel as a fine sediment and is removed with the wine's next racking or filtration.

Fining is usually one of the last steps before bottling. It is used when a wine is hazy, when tannins feel excessively dry or green, or when the winemaker wants to guard against protein instability — the haze that can form in white wines exposed to heat.

Common fining agents

• Bentonite — a clay used mainly on white wines to remove excess protein and prevent haze. It is inert and settles out cleanly.
• Egg white — traditional in Bordeaux and Burgundy for softening harsh tannins in red wine. The albumen binds to phenolic compounds and is removed by racking.
• Gelatin and isinglass — animal-derived proteins used to reduce astringency and improve brilliance, especially in white and sparkling wines.
• Casein and skim milk — milk proteins used to clarify white wines and reduce oxidative browning without adding flavour.
• Carbon — occasionally used to correct colour flaws or off-odours, though it can remove desirable aromatics if used heavily.
• Plant-based alternatives — pea protein, potato protein and other vegan agents are increasingly common as wineries respond to dietary and ethical preferences.

What fining changes

A well-judged fining can make a wine feel more supple and look more brilliant. In reds, egg-white fining rounds off the edges of tannin without removing the wine's structure. In whites, bentonite removes protein haze while leaving fruit and acidity intact. In almost every case, the aim is correction rather than transformation.

Over-fining is the constant risk. Too much bentonite can strip aroma and mouthfeel from a white wine; too much gelatin can rob a red of colour and body. Experienced winemakers taste repeatedly and fine only when the wine truly needs it.

Where you find it in France

• Bordeaux — many top châteaux still fine their reds with egg whites before bottling, a practice recorded for centuries.
• Burgundy — both reds and whites may receive light fining to polish the wine while preserving terroir expression.
• Champagne — fining agents help clarify base wines before blending and secondary fermentation.
• Natural wine cellars — many natural winemakers avoid fining altogether, preferring time and gravity to clarify the wine. Their bottles may carry a little haze as a result.

Fining and filtration

Fining is often followed by filtration, but they are not the same thing. Fining causes particles to clump and fall; filtration physically removes them. A wine can be fined without being filtered, and vice versa. Some producers believe that gentle fining followed by minimal filtration preserves more character than aggressive filtration alone.