The Chemistry of Wine, Key Compounds and Winemaking Steps

What is wine made of?

Wine is mostly water and alcohol. Compound Interest, whose infographic by Andy Brunning is on this page, puts an average red wine at about 86% water and 12% ethanol, with around 1% glycerol, 0.4% acids and just 0.1% tannins and other phenolic compounds [1]. The rest is a mix of sugars, minerals, dissolved carbon dioxide, aroma compounds and preservatives. Estimates of the total number of different compounds in a red wine range from about 800 to more than 1,000 [1].

That is why there is no chemical formula for wine. It is a mixture, not a single substance. The nearest thing is the formula for the alcohol it contains, ethanol, which is C2H5OH [4]. Wikipedia sums wine up as a complex mixture of compounds in a water and alcohol solution with a pH of around 4 [5].

Component	Share of an average red wine	What it does
Water	About 86%	The base of the drink
Ethanol	About 12%	The alcohol, made from grape sugar during fermentation
Glycerol	About 1%	A by-product of fermentation
Acids (tartaric, malic, lactic and others)	About 0.4%	Freshness, sourness and protection against spoilage
Tannins and other phenolic compounds	About 0.1%	Colour, bitterness and the drying feel in your mouth

The shares are from Compound Interest [1] and will vary from wine to wine. White wines usually have far fewer phenolic compounds than reds, and sweet wines keep more sugar.

The chemistry of fermentation

Fermentation is the step that turns grape juice into wine. Yeasts feed on the sugars in the juice, mainly glucose and fructose, and convert them into ethanol and carbon dioxide. In simple form the reaction is:

C6H12O6 (sugar) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide)

The real process runs through a series of steps inside the yeast cell. Sugar is broken down in stages, a carbon atom is given off as carbon dioxide to leave acetaldehyde, and in the absence of oxygen the acetaldehyde is reduced to ethanol [2]. The carbon dioxide bubbling out of the tank is what made early winemakers describe fermenting must as “boiling”, and the word fermentation comes from the Latin for “to boil” [2]. Louis Pasteur showed the link between yeast and fermentation in the mid 19th century [2].

Most commercial winemakers use cultured strains of Saccharomyces cerevisiae, although some rely on the wild yeasts already on the grapes and in the cellar [2]. Fermentation stops when the sugar runs out or when the alcohol reaches about 15%, which is enough to stop almost all strains of yeast working [2]. That is why unfortified wines rarely go much above 15% alcohol. Temperature matters too: white wine is usually fermented at 18 to 20°C and red wine at 20 to 30°C [2].

Yeast makes more than alcohol. It also produces small amounts of glycerol, acetic and succinic acid, esters such as ethyl acetate, aldehydes and sulfur compounds, all of which affect how the wine smells and tastes [2].

Malolactic fermentation

Most red wines, and some whites such as Chardonnay, go through a second fermentation [6]. Lactic acid bacteria, usually Oenococcus oeni, convert the sharp malic acid in grapes (the acid that tastes of green apples) into softer lactic acid [6]. This lowers the acidity and gives a rounder feel in the mouth. In Chardonnay it can add a buttery flavour from diacetyl, a by-product of the reaction [6].

The wine production process step by step

Winemaking follows the same basic stages everywhere, with one big difference between red and white wine: when the skins are removed.

1. Harvest and preparation. Grapes are picked when the balance of sugar and acid is right, then the stems are removed and the grapes crushed.
2. Pressing (white wine). For white wine the juice is pressed off the skins straight away, so the skins play no further part [3].
3. Fermentation. Yeast turns the sugar into alcohol. Red wine ferments with the skins, which are kept pushed down into the juice to draw out colour, flavour and tannin.
4. Pressing (red wine). Once fermentation is finished, red wine is pressed to separate the liquid from the skins and seeds.
5. Ageing. The wine rests in steel tanks, oak barrels or other vessels. Oak barrels add some tannins of their own [1].
6. Blending and bottling. Wines from different barrels or grape varieties may be blended before the wine is filtered or fined and bottled.

Rosé sits between the two: the juice is left on red grape skins for a short time to pick up some colour and then pressed. For more on how grape varieties differ, see our page on wine grape varietals.

The compounds behind colour and taste

The compounds that make red wine look and taste the way it does are a tiny fraction of the glass. Most of them are phenolic compounds, and the most important belong to a family called flavonoids [1][7].

Anthocyanins

Anthocyanins are the pigments in the skins of red grapes, the same family of compounds that colours blackberries and autumn leaves. Their colour depends on acidity: in acidic wine they are red, while in alkaline conditions the same molecules turn blue [1]. As wine ages, anthocyanins react with other compounds to form larger complexes. The amount of free anthocyanin falls over time, but these larger complexes keep the wine red [1].

Flavan-3-ols

Flavan-3-ols such as catechin and epicatechin come mainly from the grape seeds, with some from the skins [1][7]. They make wine taste bitter. In red wine they can reach about 800 milligrams per litre, while about 20 milligrams per litre is enough for you to taste the bitterness, and more alcohol makes them taste more bitter [1]. White wine has much less, because the juice spends little time with the seeds and skins.

Tannins

Tannins are chains of flavan-3-ol units joined together. Compound Interest says a single tannin molecule can contain as many as 27 units when the grapes are harvested [1]. Tannins cause the drying, puckering feel in your mouth after a sip of red wine: they bind to proteins in your saliva and form a precipitate [1]. Some also come from oak barrels. Tannin structure changes as wine ages; it was long thought the chains grow and drop out as sediment, but more recent work suggests they may get shorter [1].

Flavonols

Flavonols such as quercetin have no taste of their own, but they help stabilise and deepen red wine colour by binding to anthocyanins, a process called co-pigmentation [1].

Acids, sulfites and other compounds

Three main acids come from the grapes themselves: tartaric, malic and citric. Lactic, acetic and succinic acids are produced during winemaking [8]. Most wines have a pH between 2.9 and 3.9 [8]. Acidity keeps wine tasting fresh, helps the yeast and protects the wine from bacteria. Too much acetic acid gives the vinegary fault known as volatile acidity [8].

Sulfur dioxide is the preservative most often added to wine, to protect it from oxidation and unwanted microbes [5]. In the US, UK and EU, wine with more than 10 milligrams per litre of sulfites must say “contains sulfites” (or “sulphites”) on the label, whether the sulfites were added or formed naturally during fermentation [9]. White and sweet wines generally contain more sulfites than dry reds [9].

Aroma comes from a large number of volatile compounds, including esters such as ethyl acetate, methoxypyrazines, terpenes such as linalool and norisoprenoids [5].

Is red wine good for you?

Probably not in the way the headlines suggest. Several of the compounds in red wine, including the flavonols and resveratrol, are antioxidants, but the amounts in wine are low. Compound Interest notes that flavonols are present at too low a concentration to be a good source compared with onions or tea, and that a study of resveratrol found the levels in red wine were not enough for any noticeable benefit [1]. Any possible benefit also has to be weighed against the harm from the alcohol itself.

Questions about the chemistry of wine

What is the chemical formula for wine?

Wine has no single formula because it is a mixture of hundreds of compounds. Its alcohol is ethanol, C2H5OH, and it is about 86% water and 12% ethanol [1][4].

What chemical compound is in wine alcohol?

Ethanol, also called ethyl alcohol. Wine also contains small amounts of other alcohols, such as glycerol and fusel alcohols made by yeast [2].

Is fermentation of wine a physical or chemical change?

A chemical change. Yeast breaks sugar molecules down and turns them into new substances, ethanol and carbon dioxide, which cannot be turned back into sugar by physical means.

What is the chemical equation for wine fermentation?

C6H12O6 → 2 C2H5OH + 2 CO2. One molecule of sugar becomes two molecules of ethanol and two of carbon dioxide.

Why does red wine dry your mouth?

Because of tannins. They bind to the proteins in your saliva, which makes it less slippery and gives the dry, puckering feel [1].

What makes red wine red?

Anthocyanins from the grape skins. Red wine ferments with the skins, so the pigments pass into the wine. White wine is pressed off the skins before fermentation [1][3].

Sources

1. Compound Interest (Andy Brunning), The Key Chemicals in Red Wine, Colour, Flavour, and Potential Health Benefits. The original infographic and article.
2. Wikipedia, Fermentation in winemaking.
3. Wikipedia, Winemaking.
4. Wikipedia, Ethanol.
5. Wikipedia, Wine chemistry.
6. Wikipedia, Malolactic fermentation.
7. Wikipedia, Phenolic compounds in wine.
8. Wikipedia, Acids in wine.
9. Wikipedia, Sulfite, section on wine and labelling.

Last reviewed 8 November 2026