Wine is roughly 86% water and 12% alcohol, with the remaining 2% responsible for nearly everything that makes one bottle taste different from another. That small fraction contains hundreds of compounds: sugars, acids, pigments, tannins, minerals, aromatic molecules, and traces of substances added during production. Here’s what’s actually in your glass.
Water and Alcohol: The Two Main Ingredients
Water makes up the bulk of any wine. It comes from the grapes themselves and serves as the solvent that carries every other flavor and aroma compound to your palate.
Ethanol, the type of alcohol produced during fermentation, accounts for about 12% of a standard table wine by volume. Some lighter wines dip to 10% or 11%, while bold reds from warm climates can reach 15% or higher. Fortified wines like port and sherry sit around 17% because extra alcohol is added during production. Ethanol contributes body, warmth, and a slight sweetness to wine, and it’s also the primary source of calories. Pure alcohol delivers 7 calories per gram, compared to 4 calories per gram for sugar, which is why a standard 5-ounce pour of dry wine still runs 120 to 130 calories even when there’s barely any sugar left.
Sugar: From Bone Dry to Dessert Sweet
Grapes start with a lot of sugar. Yeast converts most of it into alcohol and carbon dioxide during fermentation, but whatever remains is called residual sugar. The amount left behind determines how sweet the wine tastes. A dry wine contains up to about 4 grams of sugar per liter, which is low enough that most people can’t detect sweetness at all. Off-dry wines land around 12 to 18 grams per liter, giving just a hint of sweetness. Medium-sweet wines go up to 45 grams per liter, and anything above that qualifies as sweet. A late-harvest dessert wine or an ice wine can contain well over 100 grams per liter.
In a dry wine, sugar contributes very few calories. The overwhelming majority comes from alcohol itself. In sweeter styles, sugar’s caloric contribution becomes more significant.
Organic Acids and pH
Acids give wine its bright, tart, refreshing quality and help preserve it over time. Most wines have a pH between 2.9 and 3.9, making them more acidic than coffee but less acidic than lemon juice. The total acid content runs up to about 6 grams per liter.
Three primary acids come from the grapes themselves: tartaric, malic, and citric. Tartaric acid is the dominant one and is largely responsible for wine’s crisp backbone. Malic acid tastes sharper and greener, similar to a Granny Smith apple. During a secondary fermentation process common in red winemaking, bacteria convert malic acid into lactic acid, which is softer and creamier. This is why many red wines feel rounder and less tart than whites.
Glycerol and Body
After water and ethanol, glycerol is the third most abundant compound in wine, present at 4 to 10 grams per liter. Yeast produces it as a byproduct of fermentation. Glycerol adds viscosity and a subtle sense of richness, contributing to what wine drinkers call “body” or “mouthfeel.” Those slow-moving streaks you see running down the inside of your glass (sometimes called “legs”) are partly related to glycerol and alcohol interacting with surface tension.
Polyphenols: Color, Tannins, and Antioxidants
Polyphenols account for only about 0.1% of wine by volume, but they’re responsible for color, bitterness, astringency, and much of wine’s complexity. They come primarily from grape skins, seeds, and stems, which is why red wines (fermented with their skins) contain dramatically more than whites.
Anthocyanins are the pigments that give red wine its color. A young red wine that hasn’t been aged in oak barrels contains around 400 milligrams per liter. After two years of aging, that drops to roughly 90 milligrams per liter as the pigments bind together and eventually fall out as sediment. White wines contain only trace amounts.
Tannins belong to a group called proanthocyanidins, and they create that drying, astringent sensation on your tongue and gums. Red wines contain 750 to 1,000 milligrams per liter, while whites have only about 20 to 25 milligrams per liter. Resveratrol, the antioxidant compound that generated headlines about potential heart benefits, is also a polyphenol found mainly in grape skins, though its concentration in a glass of wine is quite small.
Aroma Compounds
Wine contains hundreds of volatile molecules that evaporate into your nose and create the aromas you smell. Yeast cells produce six main groups of flavor-active substances during fermentation: organic acids, higher alcohols, carbonyl compounds, sulfur-containing molecules, phenolic compounds, and volatile esters.
Esters are especially important. They fall into two categories. Acetate esters produce fruity and floral notes: isoamyl acetate smells like banana, phenyl ethyl acetate like roses and honey, and hexyl acetate contributes a sweet, perfumed character. The second group, fatty acid ethyl esters, tends toward apple-like aromas. Ethyl hexanoate gives a green apple note, and ethyl octanoate a sour apple quality. The specific balance of these esters depends on the yeast strain, fermentation temperature, and grape variety, which is why a Sauvignon Blanc smells nothing like a Pinot Noir even before oak or aging enters the picture.
Terpenes, which come from the grapes rather than the yeast, are responsible for the floral and citrus aromas in varieties like Riesling and Muscat.
Minerals
Wine contains small amounts of potassium, magnesium, calcium, phosphorus, and other minerals absorbed by grapevines from the soil. A 5-ounce glass of white wine provides roughly 104 milligrams of potassium, 15 milligrams of magnesium, and 26 milligrams of phosphorus. These aren’t nutritionally significant amounts compared to what you’d get from food, but potassium in particular interacts with acidity and can influence how the wine tastes. Vitamins are present in only negligible quantities. Wine is not a meaningful source of any vitamin.
Biogenic Amines
Fermentation doesn’t just produce alcohol and pleasant aromas. Bacteria, particularly during the secondary fermentation that softens acidity in red wines, also generate biogenic amines by breaking down amino acids. The two most notable are histamine and tyramine. Red wines carry median histamine levels around 2.45 milligrams per liter, while white wines average just 0.28 milligrams per liter. Tyramine follows a similar pattern: about 3.20 milligrams per liter in reds versus 0.31 in whites.
For most people, these levels cause no problems. But individuals who are sensitive to histamine, or who have lower levels of the enzyme that breaks it down, may experience headaches, flushing, or nasal congestion after drinking red wine in particular.
Additives and Processing Aids
Wine isn’t just grapes, yeast, and time. Winemakers routinely use a range of permitted additives and processing aids, most of which are removed before bottling.
Sulfur dioxide (often listed as “sulfites” on the label) is the most common preservative. It prevents oxidation and inhibits unwanted bacterial growth. Nearly all wines contain some sulfites, either added or produced naturally by yeast during fermentation. Labels must declare their presence when concentrations reach 10 milligrams per kilogram or more.
Fining agents are used to clarify wine and remove haze, off-flavors, or excess tannin. Common ones include bentonite (a type of clay), activated carbon, egg white, casein (a milk protein), gelatin, and isinglass (derived from fish bladders). These are filtered out before bottling, but trace residues can remain, which is why wines fined with egg, milk, or fish products must carry allergen statements in many countries. PVPP, a synthetic polymer, is sometimes used to reduce bitterness or browning.
If you’re looking for wines with fewer interventions, bottles labeled “natural wine” or “minimal intervention” typically avoid most of these additives, though there’s no universal legal definition for those terms.