Wine is roughly 86% water, 13% alcohol (almost entirely ethanol), and 1% everything else. That last 1% is where things get interesting, because it contains hundreds of compounds that determine how wine tastes, smells, and affects your body. A standard 5-ounce glass of red wine has about 125 to 150 calories and 3 to 4 grams of carbohydrates, while white wine runs slightly lower at 121 to 148 calories per glass.
Water and Alcohol
Water is the single largest component of any wine. The ethanol, which makes up the remaining 13% or so, is produced during fermentation when yeast converts the natural sugars in grape juice into alcohol and carbon dioxide. Table wines typically sit around 12% alcohol by volume, though lighter styles can dip below that and fuller-bodied reds can push past 14%. Fortified wines like sherry and port reach about 17% because extra alcohol is added during production.
Sugars and Sweetness
Not all sugar gets converted to alcohol. What remains after fermentation is called residual sugar, and it varies dramatically by style. Many grocery store wines labeled “dry” actually contain around 10 grams per liter of residual sugar. Noticeably sweet wines start at roughly 35 grams per liter and climb from there. A bone-dry wine has very little residual sugar left, which is why it tastes crisp and tart rather than fruity or sweet. This residual sugar is the main source of carbohydrates in your glass.
Organic Acids
Wine gets its tartness from organic acids, primarily tartaric acid and malic acid. In white wines, tartaric acid concentrations typically range from about 1 to 2.5 grams per liter, while malic acid can range more widely, from roughly 1.8 to over 6 grams per liter. Citric acid is also present but in much smaller amounts. These acids do more than shape flavor. They lower the wine’s pH, which helps preserve it naturally and gives it that bright, refreshing quality. If you’ve ever noticed small crystals at the bottom of a wine bottle, those are tartrate crystals, a harmless byproduct of tartaric acid.
Phenolic Compounds
Phenolics are the compounds responsible for color, bitterness, astringency, and many of wine’s purported health properties. They fall into two broad groups: flavonoids and non-flavonoids.
In red wine, the most abundant phenolics are anthocyanins, pigments found in grape skins that account for 50 to 60% of the total phenolic content. These are what make red wine red. Flavanols, concentrated in grape seeds and stems, are the main source of tannins, which create that drying, grippy sensation in your mouth. White wines have far fewer phenolics because the juice spends little time in contact with the skins.
Resveratrol, a stilbene compound found mostly in grape skins, gets the most public attention. Pinot Noir wines can contain up to 16 milligrams per liter, among the highest levels of any variety. Another phenolic worth noting is quercetin, which can reach about 13 milligrams per liter in Shiraz wines. These amounts are small in absolute terms, but they’re the basis for much of the research into wine and health.
Glycerol and Fermentation Byproducts
Yeast doesn’t just produce alcohol. Fermentation generates a range of secondary compounds that shape how wine feels and smells. Glycerol is the most significant of these, present at 4 to 15 grams per liter. It’s a slightly sweet, viscous compound that contributes to what winemakers call “body” or “mouthfeel,” giving wine a fuller, rounder texture. Glycerol also influences how strongly you perceive aromas by affecting the way volatile compounds are released from the glass.
Esters contribute fruity and floral aromas. Aldehydes add nutty or apple-like notes (and are associated with oxidized wine when present in excess). Fusel alcohols, produced in small quantities alongside ethanol, contribute complexity at low levels but can taste harsh or solvent-like when concentrations are too high. The balance among all these byproducts is a major reason why two wines made from the same grape can smell and taste completely different.
Minerals
Wine contains a surprisingly wide range of minerals absorbed by grapevines from the soil. Potassium is the most abundant, ranging from 200 to 2,000 milligrams per liter. Calcium averages about 80 milligrams per liter. Sodium is present at lower levels, typically 10 to 300 milligrams per liter. Magnesium and phosphorus also show up in meaningful concentrations.
Trace amounts of heavier elements like iron (1 to 10 milligrams per liter), manganese, boron (roughly 20 to 50 milligrams per liter in grape juice), and copper (usually under 0.3 milligrams per liter in finished American wines) round out the mineral profile. The specific mineral content depends heavily on where the grapes were grown, which is part of what winemakers mean when they talk about “terroir.”
Sulfites
Sulfites occur naturally during fermentation, and most winemakers add more as a preservative. Sulfur dioxide prevents oxidation and kills unwanted bacteria, which is why it has been used in winemaking for centuries. U.S. federal regulations cap sulfite levels in finished wine, and any wine containing more than 10 parts per million must carry a “contains sulfites” label. In practice, sweet white wines tend to have the highest sulfite levels because sugar makes wine more vulnerable to spoilage. Dry red wines generally contain less added sulfite because their tannins provide some natural protection. People with sulfite sensitivity, particularly those with asthma, can experience reactions, but this affects a small percentage of the population.
Fining Agents and Hidden Ingredients
Wine labels don’t list ingredients the way food packaging does, which means many drinkers are unaware of what gets used during production. Fining agents are added to clarify wine by binding to unwanted particles and settling them out. The agent is then removed, so it doesn’t remain in the finished product in significant amounts, but traces can linger.
Bentonite, a type of clay, is one of the most common fining agents and is classified as generally recognized as safe by the FDA. Egg whites are a traditional choice for smoothing tannins in red wine. Casein, a milk protein, is considered one of the most effective fining agents because it leaves little residue. Isinglass, derived from fish bladders, is another option. These animal-derived agents are why some wines aren’t suitable for vegans, even though wine is a grape product. Vegan-friendly wines rely on mineral-based fining agents like bentonite or skip fining altogether, bottling the wine unfiltered.
How Red and White Wines Differ
The compositional gap between red and white wine comes down mostly to skin contact. Red wines are fermented with the grape skins, which loads them with anthocyanins, tannins, and higher levels of resveratrol and other phenolics. White wines are pressed off the skins early, resulting in lower phenolic content, lighter body, and generally higher acidity. Calorie counts are close, with red wine averaging about 125 per glass and white about 121. Both contain roughly 4 grams of carbohydrates per 5-ounce serving, though sweeter styles will have more.