Wine is made from grapes, yeast, and very little else. Crushed grapes provide the sugar, flavor, and color, while yeast converts that sugar into alcohol and carbon dioxide. The simplicity of that core recipe is what makes wine fascinating: the grape variety, the soil, the climate, and the winemaker’s choices during fermentation and aging all shape what ends up in your glass.
Grapes: The Primary Ingredient
Nearly all wine comes from varieties of a single grape species, Vitis vinifera, which includes familiar names like Cabernet Sauvignon, Chardonnay, Merlot, and Pinot Noir. Every part of the grape contributes something different to the finished wine.
The pulp is mostly water and sugar. That sugar is the fuel for fermentation, the process that creates alcohol. The skin contributes color, flavor, and a class of plant compounds called polyphenols that affect how wine tastes and feels in your mouth. Red wine gets its color from pigments in dark grape skins called anthocyanins, which can range from 90 to over 700 mg per liter depending on the grape and how long it ages. White wines skip most skin contact, which is why their polyphenol concentration is dramatically lower: roughly 0.2 to 0.5 grams per liter compared to 1 to 5 grams per liter in reds.
Grape seeds and skins also contain tannins, the compounds responsible for that dry, gripping sensation you feel when drinking a bold red. Research on Pinot Noir grapes shows that skin tannins are extracted into wine far more readily than seed tannins, and growing conditions directly influence how much ends up in the bottle. Seeds contribute additional tannins, but their extraction depends heavily on how the grapes are pressed and how long they soak.
How Yeast Turns Juice Into Wine
Fermentation is the chemical reaction at the heart of winemaking. Yeast, most commonly a species called Saccharomyces cerevisiae, consumes the sugar in grape juice and produces two main byproducts: ethanol (alcohol) and carbon dioxide gas. The chemistry is straightforward. Theoretically, yeast converts sugar into nearly equal masses of ethanol and CO₂, with about 51% becoming alcohol and 49% becoming gas by weight.
In practice, the conversion is less efficient. Some sugar goes toward keeping the yeast alive and multiplying, and some alcohol evaporates during the process. Real-world yields run about 90% of the theoretical maximum. According to the Australian Wine Research Institute, it takes roughly 16.4 to 18 grams of sugar per liter of juice to produce each 1% of alcohol in the finished wine. A grape harvest with very ripe, sugar-rich fruit will naturally produce a higher-alcohol wine.
Some winemakers rely on wild yeast already present on grape skins and in the winery. Others add commercially cultivated yeast strains chosen for predictable results or specific flavor characteristics. The yeast strain matters: different strains produce slightly different amounts of alcohol from the same sugar level and generate varying levels of aromatic byproducts that influence the wine’s smell and taste.
What Gives Wine Its Flavor and Body
Beyond alcohol, wine contains hundreds of compounds that contribute to its aroma, taste, and texture. Organic acids are among the most important. Tartaric acid is the dominant acid in wine, typically present at concentrations around 3.5 to 4.0 grams per liter. Malic acid (the same acid that makes green apples tart) contributes another 1.2 to 1.6 grams per liter. These acids keep wine’s pH between about 3.0 and 3.6, making it more acidic than coffee but less acidic than lemon juice. That acidity is what gives wine its freshness and structure.
Many red wines go through a second fermentation called malolactic fermentation, where bacteria convert sharp malic acid into softer lactic acid. This is why some reds and barrel-aged whites taste rounder and creamier than crisp, unoaked whites.
Resveratrol, the compound often cited in discussions about wine and health, is present in red wine but at very low concentrations, generally 0 to 5 mg per liter. Merlot tends to have the highest levels among commonly tested varieties, at around 5 mg/L, while Cabernet Sauvignon and Syrah come in lower, around 1.3 and 2.1 mg/L respectively.
Oak Aging and What It Adds
When wine ages in oak barrels, the wood acts as an ingredient. Compounds from the oak slowly leach into the wine, adding flavors that don’t come from grapes at all. Vanillin, the same compound that gives vanilla its smell, is one of the most recognizable. Oak also contributes compounds that create coconut, spice, and woody notes, along with a subtle sweetness and smoother texture. The barrel’s interior is typically toasted or charred before use, and the level of toasting changes which flavors are most prominent.
New barrels contribute more flavor than barrels that have been used multiple times. Winemakers who want just a hint of oak influence might use older barrels, while those seeking bold vanilla and spice notes choose new ones. Some producers use oak chips or staves inserted into steel tanks as a less expensive alternative to barrels, achieving similar (though not identical) flavor effects.
Common Additives in Winemaking
The romantic image of wine as “just grapes” is mostly true, but winemakers do use a short list of additives to stabilize, clarify, and fine-tune their product.
- Sulfites (sulfur dioxide): The most common additive, used to kill unwanted bacteria and prevent oxidation. Nearly all commercially produced wine contains added sulfites, and even wines labeled “no added sulfites” contain small amounts produced naturally during fermentation.
- Tartaric, malic, or citric acid: Added when grapes don’t have enough natural acidity. This is especially common in warmer growing regions where ripe grapes can taste flat without a boost.
- Sugar or grape concentrate: In cooler wine regions, sugar is sometimes added before fermentation (a practice called chaptalization) to raise the potential alcohol level. This is regulated differently by country.
- Fining agents: Substances used to clarify wine by binding to unwanted particles so they settle out. Common options include bentonite (a volcanic clay that attracts and removes excess proteins), egg whites (which bind to harsh tannins and reduce astringency), and casein (a milk protein that works similarly to egg whites). These agents are removed from the wine before bottling, but trace amounts may remain, which matters for people with egg or dairy allergies.
The fining process works through basic chemistry. Bentonite clay acts like an ion exchange system: positively charged proteins in the wine swap places with metal ions on the clay’s surface, forming a complex that sinks to the bottom of the tank. Protein-based fining agents like egg whites work the way saliva does when you drink tannic wine. The proteins bind to tannins, forming clumps that fall out of suspension, leaving the wine smoother and clearer.
What’s on the Label (and What Isn’t)
Wine has historically been one of the least transparent products on grocery shelves when it comes to ingredient disclosure. Unlike packaged food, wine in the United States still has no requirement to list ingredients beyond allergen warnings for sulfites. The European Union changed this with Regulation 2021/2117, which now requires all wines produced from December 2023 onward to declare their energy value and allergens directly on the label. A complete ingredient list and full nutritional breakdown can be provided either on the label itself or through a QR code printed on the bottle.
This means European wine labels now must show calories per 100 ml and flag common allergens like sulfites, egg, and milk derivatives. The full ingredient list, when you scan the QR code, appears in descending order by weight, just like food packaging. For consumers who want to know exactly what’s in their wine, these labels are a significant step forward.