Ripening & the Grape's Changing Components

From Flower to Fruit: The Start of the Growing Season

Before a grape can ripen, the vine must first flower and set fruit. Flowering happens in late spring in most wine regions, when small greenish flowers appear on the vine and are pollinated — almost always by wind rather than insects, since most wine grape varieties are self-pollinating. Flowering is a delicate stage: cool, wet, or windy weather at the wrong moment can cause poor pollination, reducing the number of berries that ultimately form and cutting that year's potential yield.

Successful pollination leads to fruit set, when fertilized flowers begin to develop into tiny, hard, green berries. At this stage the berries are full of acid and have almost no sugar — they do not yet resemble the grapes used to make wine.

Veraison: The Turning Point

The single most important moment in the ripening process is veraison, which typically occurs six to eight weeks after flowering. Veraison is the point at which berries begin to change color and soften:

• White grapes turn from hard and green to a translucent yellow or golden color.
• Black grapes turn from green to red, purple, or near-black as anthocyanin pigments develop in the skin.

Veraison marks a shift in the vine's priorities, from vegetative growth (leaves and shoots) toward ripening the fruit. From this point on, sugar accumulates rapidly in the berries as the vine's leaves send the products of photosynthesis into the fruit.

How the Grape Changes as It Ripens

Between veraison and harvest, every major component of the grape changes in a predictable direction:

For black grapes, winemakers must track two things at once: the sugar-and-acid balance in the pulp, and the "phenolic ripeness" of the tannins in the skin and seeds. If grapes are picked when sugar and acid look right but the tannins are still unripe and green, the resulting wine can taste harsh and bitter even though the alcohol level and acidity seem correct. This is one reason producers of premium red wine often taste grapes in the vineyard, biting into skins and seeds, rather than relying on sugar readings alone. For white grapes, skin tannin ripeness matters far less, since white wines are typically made with minimal skin contact — the priority is usually the sugar-and-acid balance and the development of the desired aroma and flavor profile.

Unripe, Ripe, and Extra-Ripe Grapes

Grapes can be picked at different stages of ripeness depending on the style of wine a producer wants to make:

• Unripe grapes — high in acid, low in sugar, with green, tart, herbaceous flavors and, for black grapes, pale color and harsh tannins. Deliberately picking early is sometimes used for lighter, crisper, lower-alcohol wine styles, or for sparkling wine base wines that need high natural acidity.
• Physiologically ripe grapes — the target most producers aim for: a balance of ripe flavors, moderate sugar, and retained acidity, with, for black grapes, ripe and soft tannins along with good color.
• Extra-ripe or overripe grapes — left on the vine well past normal ripeness. Sugar levels climb further, acid drops further, and flavors shift toward dried fruit, honey, and jam-like character. This can happen through late harvest picking, or through deliberate raisining — leaving bunches on the vine, or drying them after picking, so water evaporates from the berries and sugar becomes further concentrated. Extra-ripe and raisined grapes are the starting point for many sweet wine styles covered later in this guide.

Recognizing where a grape sits on this ripeness spectrum, and understanding why a grower chooses a particular picking date, is fundamental to understanding why wines made from the same grape variety can taste so different depending on when the fruit was harvested. A grower picking for a crisp, dry white will make very different decisions from one picking late-harvest fruit destined for a lusciously sweet wine, even if both start with the same grape variety in the same vineyard.

Where Ripening Fits in the Full Growing Cycle

Flowering, fruit set, veraison, and ripening are the middle stages of an annual cycle that repeats every year of a vine's productive life. The cycle begins with budburst in early spring, when the dormant vine's buds swell and small green shoots emerge, followed by leaf and shoot growth through late spring. After flowering, fruit set, and the ripening stages described above, the cycle ends with harvest, and then the vine sheds its leaves and enters winter dormancy, resting until budburst begins the cycle again the following spring. A grower's decisions at every stage of this cycle — how hard to prune during dormancy, how to manage the canopy during the growing season, and ultimately when to pick — all build toward the ripening outcome described in this section.