How Wine Is Made: From Grape to Glass

Everything in winemaking flows from a single, irreversible choice: when to pick. Grapes stop ripening the moment they are removed from the vine, so the winemaker's timing locks in the fruit's sugar level, acidity, and tannin ripeness permanently. Pick too early and the wine will taste sharp and thin. Pick too late and it risks being flabby, overripe, or damaged by rain and rot. Harvest timing is determined through a combination of laboratory measurements and old-fashioned tasting. Sugar content is commonly measured in Brix (a scale where one degree Brix equals roughly one gram of sugar per 100 grams of liquid), while acidity is measured in pH and titratable acidity. But numbers only tell part of the story; experienced winemakers walk the rows, tasting grapes and checking the color and texture of the seeds. White grapes are typically harvested earlier than reds to preserve their natural acidity and freshness. Once the decision is made, picking happens either by hand or by machine. Hand harvesting allows careful selection of individual bunches and is gentler on fragile fruit, while machine harvesting is faster and more practical for large estates. In warmer regions like parts of California or Australia, harvest often happens at night to keep the grapes cool and preserve aromatics.

• Sugar in grapes is measured in Brix; roughly 17 grams of sugar per liter are needed per 1% ABV of finished wine.
• White grapes are typically harvested earlier than reds to preserve acidity and delicate aromas.
• Hand picking allows selective harvesting but is labor-intensive; machine harvesters are efficient but less precise.
• Night harvesting is common in warm regions to keep grapes cool and protect fresh, aromatic compounds.

Once grapes arrive at the winery, the first job is to sort out anything that does not belong: underripe or rotten clusters, leaves, and stems. Many premium wineries use sorting tables, either by hand or with optical sorting machines, to cull unwanted fruit before crushing begins. The next step is destemming, which removes the grapes from their woody stalks. Stems contain green, vegetal tannins that most winemakers prefer to exclude, though some deliberately retain a portion of whole clusters to add structure or spice, a technique common in Pinot Noir production in Burgundy. Crushing gently breaks the grape skins to release the juice. Modern wineries use a mechanical crusher-destemmer, which simultaneously removes stems and cracks the berries. The resulting mixture of juice, pulp, skins, and seeds is called must. At this point, the paths for red and white wine diverge. For white wine, the winemaker moves quickly to press the must and separate the juice from the skins. For red wine, the skins stay in contact with the juice throughout fermentation, which is the key to the wine's color, tannin, and much of its body.

• Sorting removes rotten, underripe, or damaged fruit before crushing; optical sorters are used at many premium estates.
• Destemming removes woody stalks, though some winemakers retain whole clusters for added structure.
• The mixture of crushed grape juice, skins, seeds, and pulp is called 'must.'
• White wine must is pressed immediately; red wine must ferments with the skins still present.

Fermentation is the core transformation of winemaking. Yeast, a single-celled fungus, consumes the sugars in grape juice and converts them into ethanol (alcohol) and carbon dioxide. The primary workhorse is Saccharomyces cerevisiae, the same species used in beer and bread. This yeast is exceptionally well-suited to winemaking because of its tolerance for both the high sugar concentration of fresh grape juice and the rising alcohol levels as fermentation progresses. Winemakers have two choices: inoculate with commercially cultured yeast strains, which are reliable and produce consistent, predictable results, or allow native yeasts already present on the grape skins and in the winery environment to do the work. Natural, or spontaneous, fermentation using wild yeasts is less predictable but often produces more complex and distinctive aromas. Beyond producing alcohol and carbon dioxide, yeast also creates dozens of secondary compounds during fermentation, including esters (which contribute fruity and floral aromas), higher alcohols, and small amounts of acetic acid. Temperature control during fermentation is critical: red wines are typically fermented warmer than whites to encourage color and tannin extraction, while white wines are fermented at cooler temperatures, between roughly 12 and 22 degrees Celsius, to preserve delicate fruit and floral character. Fermentation for red wines generally takes about two weeks. If a winemaker wants a sweeter finished wine, fermentation can be stopped early before all sugar is consumed.

• Yeast converts grape sugar to ethanol and carbon dioxide; the primary wine yeast is Saccharomyces cerevisiae.
• Winemakers choose between cultured commercial yeasts (reliable, consistent) or native wild yeasts (less predictable, often more complex).
• White wines ferment at cooler temperatures (roughly 12 to 22 degrees Celsius) to preserve aromatic freshness.
• Stopping fermentation early leaves residual sugar, resulting in off-dry or sweet wine styles.

The single biggest difference between red and white winemaking is skin contact. Red wine is made from dark-skinned grapes, and the juice ferments together with those skins, seeds, and sometimes stems. This process, called maceration, extracts the compounds that define red wine: color comes from pigments called anthocyanins found exclusively in the skins, and structure comes from tannins, which are natural compounds that create the dry, gripping sensation on the palate and allow red wines to age gracefully. During fermentation, carbon dioxide pushes the grape skins to the surface, forming a thick cap. Winemakers must break this cap up regularly, either by punching it down with a tool or by pumping the liquid from the bottom of the tank over the top. Pump-overs extract more intensely and produce richer reds; punch-downs are gentler and tend to yield more delicate wines. White winemaking works on the opposite principle: it is about separation and protection. Grapes are pressed immediately after crushing, removing skins and seeds before fermentation begins. The clear juice then ferments in a temperature-controlled environment designed to preserve the grape's inherent freshness, fruit, and aroma. Rosé wine sits between the two: red grapes are briefly macerated for a few hours to extract just a blush of color before the juice is pressed and fermented like a white.

• Red wine color comes from anthocyanins in the grape skins; without skin contact, there is no red wine.
• Tannins, which give red wine its structure and aging potential, are extracted from skins, seeds, and sometimes stems during maceration.
• Pump-overs extract flavor more vigorously; punch-downs are gentler and preserve more delicacy.
• White wine is pressed immediately after crushing; the skin-free juice then ferments at cool temperatures to protect freshness.

After alcoholic fermentation is complete, many wines undergo a second biological transformation called malolactic fermentation, or MLF. This is not technically a fermentation in the traditional sense but a bacterial process in which lactic acid bacteria, primarily Oenococcus oeni, convert malic acid into lactic acid and carbon dioxide. Malic acid is the sharp, tart acid associated with green apples; lactic acid is softer and creamier, like the acidity in milk or yogurt. The result is a wine that feels rounder and less sharply acidic on the palate. Virtually all red wines go through MLF, as do many white wines, particularly Chardonnay. Grapes grown in cool regions like Burgundy, Champagne, or Germany's Mosel tend to be naturally high in malic acid, and MLF is especially important for achieving balance in those wines. Winemakers who want to preserve a wine's bright, crisp acidity, such as in an aromatic Riesling or Sauvignon Blanc, will actively prevent MLF by adding sulfur dioxide or keeping temperatures cold, both of which inhibit the bacteria. The famous buttery or creamy texture associated with many California Chardonnays is largely the product of full malolactic conversion combined with oak aging. MLF also improves the wine's biological stability, because the bacteria consume nutrients that other spoilage microbes would otherwise feed on.

• MLF converts sharp malic acid (green apple) into softer lactic acid (cream), reducing the wine's perceived acidity.
• Nearly all red wines and roughly 20% of the world's white wines undergo malolactic fermentation.
• Winemakers block MLF in aromatic whites like Riesling and Gewurztraminer to preserve their vibrant, crisp acidity.
• MLF also improves microbial stability by removing nutrients that spoilage organisms would otherwise consume.

Once fermentation is complete, the winemaker faces one of the most consequential decisions in the entire process: where and how long to age the wine. The vessel chosen is not passive storage; it actively shapes the wine's flavor, texture, and structure. Oak barrels are the most traditional choice for premium wines. New oak adds flavor compounds including vanilla, spice, toast, and in some cases chocolate or mocha notes, and allows slow, controlled exposure to small amounts of oxygen through the wood's pores. The size of the barrel matters: the standard 225-liter Bordeaux barrique has a high ratio of wood surface to wine volume, imparting more oak character quickly, while large Italian botti or French foudres of 1,000 liters or more add very little oak flavor but allow gentle oxygenation. Stainless steel tanks are completely inert and airtight, preserving the wine's primary fruit flavors and crisp acidity with no added flavors whatsoever. Sauvignon Blanc from Marlborough and Riesling from the Mosel are almost always steel-fermented and aged for exactly this reason. Concrete tanks, once considered old-fashioned, have staged a major comeback. Like oak, concrete is slightly porous and allows micro-oxygenation, which gently softens tannins and adds texture; unlike oak, it imparts no flavor, letting the grape speak clearly. Clay amphorae are the oldest winemaking vessel in human history, with archaeological evidence of use dating back approximately 6,000 years. Like concrete, they are porous but flavor-neutral, creating wines with earthy character, gentle texture, and what many winemakers describe as pure terroir expression. Most dry reds need 18 to 24 months of aging before bottling, while many whites are bottled after just a few months.

• New oak barrels add vanilla, spice, and toast flavors and allow slow oxygen exchange; barrel size determines the intensity of oak influence.
• Stainless steel is fully inert and preserves primary fruit and acidity without adding any flavor.
• Concrete tanks allow gentle micro-oxygenation like oak but add no flavor, producing wines with texture and minerality.
• Clay amphorae, used for over 6,000 years, are porous and flavor-neutral, favored for their pure expression of grape and terroir.

Before a wine can be bottled, it must be stable and clear. After fermentation and aging, wine contains suspended particles including dead yeast cells, grape fragments, proteins, and tannin compounds that can cloud the liquid or cause unwanted changes in the bottle. Winemakers address this through two related but distinct processes: fining and filtration. Fining involves adding a clarifying agent to the wine that binds to unwanted particles and pulls them out of suspension, sinking to the bottom of the vessel where they can be removed by racking, or siphoning the clear wine off the top. Common fining agents include egg whites, which are added at a rate of roughly five to eight egg whites per barrel for fine red wines and are particularly effective at softening harsh tannins; bentonite clay, a volcanic ash-derived mineral that removes unstable proteins from white wines and prevents clouding at high temperatures; and casein, a milk protein used primarily for white wines. Filtration is a separate, complementary step in which wine is passed through filter media to remove particles by physical size. Some winemakers, particularly natural wine producers, choose not to fine or filter, believing the processes strip texture and complexity. This is a legitimate philosophical position, though unfined and unfiltered wines require more careful handling. A final dose of sulfur dioxide is typically added just before bottling to preserve freshness and prevent unwanted fermentation in the bottle. The wine is then sealed, traditionally with cork, though screw caps and synthetic closures are now widely used and offer their own advantages in consistency and protection from cork taint.

• Fining uses agents like egg whites, bentonite clay, or casein that bind to particles and cause them to sink for removal.
• Filtration physically removes particles by size; sterile filtration can remove all remaining yeast and bacteria.
• A final addition of sulfur dioxide before bottling preserves freshness and prevents refermentation in the bottle.
• Some winemakers skip fining and filtration entirely, believing these steps can strip texture and complexity from the wine.