Véraison — The Onset of Grape Ripening

Véraison is the start of grape ripening, when color change begins. It sits within a three-phase pattern of berry development. Phase 1 starts soon after fruit set, with growth of the seed and the berry; at this point the final number of cells in the berry is determined and acids accumulate. Phase 2 is known as the lag phase, because the berry grows only slowly while the seed matures. Towards the end of Phase 2 the berry starts to soften and to color, and this is known as véraison. Véraison marks the beginning of Phase 3, the period of rapid cell expansion and sugar accumulation.

• Phase 1: starts soon after fruit set; the final number of cells in the berry is determined and acids accumulate
• Phase 2 (lag phase): slow berry growth while the seed matures; it lasts between 7 and 40 days depending on variety and temperature, and it is the most temperature-sensitive stage
• Phase 3: begins at véraison, with rapid cell expansion and sugar accumulation
• The growth stages in order: budburst, flowering, setting (fruit set), véraison and harvest

Abscisic acid (ABA) is made in the seed during Phase 2. Late in Phase 2, ABA is exported from the seed into the pulp and initiates ripening. In Phase 3, hormones activate the genes that make the enzymes for importing sugar into the berry. Color is building before it shows: anthocyanins begin to accumulate in the skins of red varieties about two weeks before the color is visible, and the most important period for phenolic development is the 2 to 3 weeks before véraison. In red varieties, the levels of tannins in grape skins are already relatively high at véraison and remain essentially constant thereafter, while in white grapes phenolic compounds diminish to minimal concentrations as berries mature.

• ABA, made in the seed, is exported into the pulp late in Phase 2 and initiates ripening
• Red varieties: anthocyanins accumulate in the skins about two weeks before color is visible
• Red varieties: skin tannin levels are already relatively high at véraison and stay essentially constant; the ability to extract seed tannins decreases after véraison
• White varieties: phenolic compounds diminish to minimal concentrations as berries mature

Phase 3 is the stage at which potassium, amino acids and phenolic compounds increase, malic acid is degraded, and most flavors are developed. Sugar accumulation is generally more rapid in the weeks following véraison and usually becomes slower later. Berries cannot draw energy for their metabolism from sugars during this phase; instead, for most needs, malic acid in the berry is drawn upon and broken down to provide energy. The amount of tartaric acid per berry stays constant during ripening, but its concentration falls as the berry grows in volume. Aromas shift too: the methoxypyrazines responsible for the capsicum and asparagus aromas of some wines decrease as berries mature, while the terpenoids that give floral or citrus aromas increase. Methoxypyrazines can be retained in fruit under cool conditions, shading of bunches and minimal water stress. Berry cell walls gradually weaken as pectin is dissolved during ripening.

• Sugar: accumulation is generally more rapid in the weeks after véraison, then usually slows
• Acid: malic acid is broken down to provide energy; tartaric acid per berry stays constant while its concentration falls as the berry grows
• Aroma: methoxypyrazines (capsicum, asparagus) decrease; terpenoids (floral, citrus) increase
• Texture: berry cell walls gradually weaken as pectin is dissolved

In a colored grape variety, green berries start changing to red or blue; in a green grape variety, the berry becomes more translucent. The modified E-L system gives each step a number: at stage 34 berries begin to soften and sugar starts increasing, stage 35 is véraison, when berries begin to color and enlarge, stage 36 is berries with intermediate sugar values, and stage 38 is harvest, when berries are harvest-ripe. When growth stages are recorded in field trials, the date of a stage is noted when 50% of the tagged buds or shoots have reached it. Some ripening processes do occur before there are any visible signs of véraison, and bunches removed from the vine before véraison generally do not ripen to maturity.

• Colored varieties: green berries start changing to red or blue
• Green varieties: berries become more translucent
• E-L 34: berries begin to soften, sugar starts increasing; E-L 35: véraison, berries begin to color and enlarge; E-L 38: harvest
• Stage dates are recorded when 50% of the tagged buds or shoots reach the stage

Phase 2, the lag phase that ends at véraison, lasts between 7 and 40 days, and its length depends on both variety and temperature; it is the most temperature-sensitive stage of berry development. In the Willamette Valley, véraison occurs in about mid-August.

• Phase 2 length: 7 to 40 days, depending on variety and temperature
• Phase 2 is the most temperature-sensitive stage of berry development
• Willamette Valley: véraison in about mid-August

The timing of crop thinning around véraison changes its effect. In table grapes, removing fruit clusters before véraison increases berry size, yield is less affected, and the clusters ripen sooner; thinning soon after véraison has little effect on berry size, but yield is reduced and the remaining fruit ripens sooner. As harvest approaches, there are a number of ways to define ripeness, and the one used depends on the wine style intended: juice or pulp maturity, skin maturity, phenolic maturity, aromatic maturity and seed maturity. Full lignification of the seed is desirable for red wine styles but often lags behind other measures of ripeness.

• Table grapes, thinning before véraison: berry size increases, yield is less affected, clusters ripen sooner
• Table grapes, thinning soon after véraison: little effect on berry size, yield is reduced, remaining fruit ripens sooner
• Ripeness can be defined as juice or pulp, skin, phenolic, aromatic or seed maturity, depending on the wine style intended

Primary sources: https://www.awri.com.au/wp-content/uploads/4_phenology_berry_development_1_and_2.pdf, https://www.awri.com.au/wp-content/uploads/5_phenology_berry_development_ripening_3.pdf, https://www.awri.com.au/wp-content/uploads/6_phenology_defining_berry_ripeness.pdf, https://www.awri.com.au/wp-content/uploads/grapegrowth.pdf, https://www.awri.com.au/wp-content/uploads/2014/09/on-farm-trials-manual-3-3.pdf, https://extension.oregonstate.edu/sites/extd8/files/catalog/auto/EC1639.pdf. Last verified 2026-11-02