How is wine made? Grape to bottle, step by step

Wine is made by letting yeast eat the sugar in grape juice. Everything after that is a decision, and the decisions are what separate a bottle you should finish this year from one that is still gaining at thirty.

So how is wine made? Six stages, in order: harvest, crush and destem, alcoholic fermentation, pressing, a second bacterial fermentation called malolactic, and élevage, the maturation before bottling. Red wine ferments on its skins, and pressing comes afterwards. White wine goes to the press first, then ferments as clear juice. Champagne is a still white wine given a second fermentation inside a sealed bottle. In appellation France little of this is left to the winemaker's taste. The Pomerol rulebook filed with INAO sets a minimum sugar at picking of 194 grams per litre of must for Merlot, a minimum natural alcohol of 11%, a yield of 49 hectolitres per hectare, and a rule that the wine be matured "au moins jusqu'au 1er novembre de l'année qui suit celle de la récolte": at least until the first of November of the year after the harvest. The stages are universal. The numbers bolted to them are law, and they change with the address.

What happens at harvest, and what does the law require?

Picking date fixes the sugar, and sugar becomes alcohol. That is why appellation law regulates the harvest harder than almost any later step.

The Pomerol cahier des charges is a useful example because it governs one of the most expensive red wines on earth. Grapes are not considered ripe below "194 grammes par litre de moût pour le merlot" and 180 grams per litre for the other permitted varieties, which are Cabernet Franc, Cabernet Sauvignon, Cot (Malbec), Merlot and Petit Verdot. Finished wine must reach a minimum natural strength of 11%, and must not exceed 13.5% total after any enrichment. Vines must be planted at a minimum of 5,500 per hectare, rows no more than 2 metres apart. The cahier des charges caps average crop load at 8,000 kilograms per hectare and the yield at 49 hectolitres per hectare, with a hard ceiling of 60.

Estates that matter go well past the minimum. The Wine Cellar Insider's profile of Pétrus records average yields of 40 hectolitres per hectare on 11.5 hectares of 100% Merlot, about 2,500 cases a year, and a harvest in which "the berries are picked one at a time" and "the fruit is always 100% destemmed".

Champagne solves a harder problem: making white wine from black grapes. The Union des Maisons de Champagne states the constraint plainly. Clusters must be "placed whole and intact in the press", a condition that "for the time being at least rules out mechanical harvesting". Every bunch in Champagne is picked by hand because a machine would break skins in the vineyard and bleed colour into the juice.

What is fermentation doing?

Converting sugar into ethanol, carbon dioxide and heat. The arithmetic simply: "For every gram of sugar that is converted, about half a gram of alcohol is produced."

Typical fermentation temperatures of 22 to 25°C for reds, because heat pulls colour and tannin out of the skins, and 15 to 18°C for whites, to hold onto aromatics. The whole thing "often takes between one and two weeks". Yeast is not infinitely patient: activity stops once the sugar is gone or the alcohol reaches about 15% by volume, "a concentration strong enough to halt the enzymatic activity of almost all strains of yeast".

Vessel choice is a real decision, not a detail. According to The Wine Cellar Insider, Pétrus ferments in "12 traditional, temperature-controlled, concrete vats", which give thermal mass without oak flavour during the most extractive phase of the process. Stainless steel does the same job with faster temperature response. Oak fermenters add flavour and oxygen from the first day.

Why is red wine red, and white wine not?

Skins, and how long they stay in the tank. There is no red pigment in the juice of almost any grape. It all sits in the skin.

Red wine is destemmed, crushed and fermented with the skins floating in the liquid, so pigment and tannin dissolve into the alcohol as it forms. Pressing happens afterwards, "usually ramping from 0 Bar to 2.0 Bar", and the harder-pressed fraction is a different wine from the free-run that came off under gravity. White wine reverses the order: press first, ferment the clear juice. Leave white grapes on their skins instead and you get the third category, which our orange wine guide covers in full.

Champagne shows the extreme version. Whole bunches go into wide, shallow presses, and the Comité Champagne states a press capacity of "2,000kg to 12,000kg of whole grapes", worked in 4,000-kilogram units called a marc. The Union des Maisons de Champagne specifies the permitted extraction as "102 litres of must per 160kg of pressed grapes", which works out at 2,550 litres per marc: 20.5 hectolitres of cuvée drawn off first, then 5 hectolitres of taille. The juice runs clear because the skins never sit in it.

What is malolactic fermentation, and why does nearly every serious red have it?

Because it removes an acid that tastes like green apple and replaces it with one that tastes like milk, and because leaving it undone is a microbiological time bomb in the bottle.

The AWRI describes malolactic fermentation as "a secondary bacterial fermentation carried out in most red wines", run by Oenococcus oeni, "the main bacterium responsible for conducting MLF, due to its ability to survive the harsh conditions of wine (high alcohol, low pH and low nutrients)". Its published window is narrow: ethanol below 14% by volume, temperature 18 to 22°C, pH between 3.3 and 3.5, and total sulphur dioxide under 30 milligrams per litre. Above 40 mg/L the AWRI calls conditions unfavourable, and concentrations above 50 to 60 mg/L "may completely inhibit MLF". The AWRI judges completion on residual malic acid. It advises aiming for a result of "not detected", usually below 0.05 g/L, and treats 0.1 g/L or less as finished.

Parameter	Favourable	Unfavourable
Ethanol (% v/v)	Below 14	Above 16
Temperature (°C)	18 to 22	Below 16, above 25
pH	3.3 to 3.5	Below 3.3
Total SO₂ (mg/L)	Below 30	Above 40

In Pomerol it is not optional in any practical sense. The cahier des charges requires that every lot sold, bulk or bottled, carry malic acid "inférieure ou égale à 0,30 gramme par litre". Miss the malolactic and you cannot legally sell the wine as Pomerol. At Pétrus it runs in vat, according to The Wine Cellar Insider: "after the alcoholic fermentation is completed, the juice goes through malolactic fermentation in vats", and only then does the wine go to barrel.

What does élevage do, and why does new oak cost real money?

It is where oxygen, not yeast, does the work. Élevage is the raising of the wine between fermentation and bottling, and it is the stage where the choices are least reversible.

Oak does three things at once: it adds flavour compounds, it adds tannin, and it leaks oxygen. The Union des Maisons de Champagne describes the third point directly: "Like cork stoppers, wood barrels and casks allow a slow and natural micro-oxygenation that favours wine maturation." How much oxygen is measurable and it matters. Prat-García and colleagues, publishing in Molecules in 2020, aged the same red wine in barrels built to different oxygen transmission rates, 1.29 against 0.38 hPa per litre per day, and found that "the high-OTR barrels dose the aged wines with twice the oxygen as the low-OTR barrels". After a year the wines had lost 43% of their monomeric anthocyanins in the low-oxygen barrels and 47% in the high-oxygen ones, and it was the low-oxygen wine that "presents a major intensity of colour".

New oak is the expensive version of that decision, and even at the top the percentage is a judgement, not a flex. The Wine Cellar Insider records that Pétrus goes into "an average of 50% new, French oak barrels for 18-20 months". In Champagne the working cask is 205 litres, and the Union des Maisons de Champagne notes that hoops are retightened to prolong the life of a cask "sometimes for as long as 50 years", which tells you how differently the two regions think about wood.

Then the law sets the floor. Pomerol wines must be raised "au moins jusqu'au 1er novembre de l'année qui suit celle de la récolte", may be bottled from that same first of November, and may reach consumers only from 15 November of the year after harvest. That is a legal minimum of more than a year in the cellar before a bottle of any Bordeaux 2015 Pomerol could be sold. Serious estates take longer.

How is Champagne made differently?

It is made twice. A still base wine is fermented, blended, then re-fermented inside the bottle you eventually open, which is why the sediment and the pressure are both in there. The Champagne styles guide covers what the label words mean.

Blending comes first. The Union des Maisons de Champagne calls the cellar master "the keeper of the House style if you like", tasting in January to rebuild the same signature year after year, adding reserve wines that "impart softness to the blend". In exceptional years a house may instead declare a vintage, "a wine made exclusively from the grapes grown in that year". Dom Pérignon is the purest form of that rule: it makes nothing else, and it skips the years it does not rate. Dom Pérignon has released forty-eight vintages between 1921 and 2017. There is no 2001, no 2007, no 2011, no 2014 and no 2016.

Then the second fermentation. According to the Comité Champagne, bottling "cannot take place before the first day of January following the harvests". Each bottle receives a liqueur de tirage of still wine, sugar and yeast, and is sealed and laid on its side in a cellar held at "a constant cool 9-12 degrees C". The yeast eats the sugar with nowhere for the gas to go. Pressure climbs to 6 kg/cm², "fierce at first" and tailing off within two months, and the wine gains "about 1.2-1.3 degrees" of alcohol. The bottle is "designed to withstand 12 atmospheres of pressure". For legal comparison, quality sparkling wine must carry "an excess pressure, due to carbon dioxide in solution, of not less than 3,5 bar when kept at a temperature of 20 °C", according to Regulation (EU) No 1308/2013.

The yeast then dies in the bottle. The Comité Champagne describes what follows: "By the end of second fermentation, the yeasts die and decompose. This process is known as autolysis." That decomposition is the source of the brioche character, and it takes time. According to the Comité Champagne, every Champagne must spend "at least 15 months maturing in the winemaker's cellars before release", and vintage cuvées are "matured for at least three years". Dom Pérignon runs past both. Richard Geoffroy, who ran its cellar until the end of 2018, set the house timetable out in his Manifesto: "Dom Pérignon expresses its first plénitude after seven years in the cellar", a second 12 to 15 years after the vintage, and a third at 30 to 40. Published release dates for the later bottlings vary, so read the disgorgement date on the back label rather than the tier name.

Finally the dead yeast has to come out. The Comité Champagne sets out the sequence: bottles are riddled neck-down until the sediment collects in the neck, the neck is "plunged in a solution at approximately -27°C" to freeze it into a plug, and the pressure inside blows the plug out when the bottle is opened. Large bottles and certain cuvées are still disgorged by hand, "à la volée". The bottle is topped up with a dosage of cane sugar and wine, then corked.

What happens between the last barrel and the cork?

Clarification and preservation, and both are dose decisions rather than yes-or-no ones.

Fining agents work "to remove tannins, reduce astringency and remove microscopic particles that could cloud the wines". Filtration comes in grades set by what it must catch: "at least 0.65 micrometers for yeast retention and 0.45 μm for bacteria retention". Sterile filtration buys certainty and costs texture. That is why a lot of top red goes into bottle unfiltered, and why sediment in an old bottle is normal rather than a fault.

Sulphur dioxide is the last addition. The EU caps total SO₂ at 150 milligrams per litre for red wines and 200 for white and rosé, according to Commission Delegated Regulation (EU) 2019/934. Those ceilings rise to 200 and 250 respectively where the wine carries at least 5 grams per litre of sugar, and the same annex sets 185 mg/l for all categories of quality sparkling wine. Appellations can be stricter than the EU: Pomerol holds bulk lots to 140 milligrams per litre.

After that the winemaking stops and the bottle's own history begins. What happens to the fill level, the cork and the capsule over the next forty years is a separate subject, covered in the ullage guide.

Which of these steps shows up in what you pay?

The ones that constrain supply and the ones that set the drink window. Pomerol caps yield at 49 hectolitres per hectare, and Pétrus reports averaging 40 across 11.5 hectares for about 2,500 cases. Eighteen to twenty months in half-new oak, on top of an élevage the appellation will not let end before the first of November of the following year, is why a Pomerol reaches the market more than a year after picking. Three years is the legal floor for a vintage Champagne, and Dom Pérignon sits well beyond it, which is why a vintage cuvée is not a young wine when you buy it.

The market index shows what the finished wines do once they are in the secondary market, and the Bordeaux producer atlas puts the estates on the ground they are made from, which for Pétrus is the whole story. If the wine is already in your cellar, drink-now is the page that answers when to open it rather than what it is worth.

Get the winemaking that matters, once a week

Most winemaking writing stops at the vineyard gate. Ours tells you what a producer's decision means for the bottle you are about to bid on: a change in new-oak percentage, an earlier picking date, a house switching to co-inoculation, a vintage declared or skipped.

The weekly winemaking briefing goes out to members and takes about four minutes to read. Each edition names the wines it affects and links straight to their price history and drink windows, so a change in the cellar becomes a change in your buying list rather than a piece of trivia.