Whether it’s Pinot Grigio or Cabernet Sauvignon, all wine grapes start out green and hard. Veraison is a stage in the growing process when the grape begins to soften and change color on the vine, indicating the onset of ripening.
Pronounced ver-Ray-zon, it’s both a physical and chemical transformation. It’s also a pretty conspicuous process in red-wine grapes.
“Just prior to veraison, the grape berry looks like a hard green pea,” says Paul Clifton, director of winemaking for Hahn Family Wines in Monterey County, California. “As the grapevine moves into the stage of veraison, the berry starts softening up and enlarging as it accumulates sugar, while the color begins to change, too.”
During veraison, grapes can double in size. White wine grapes become increasingly translucent, while red wine grapes turn pink and later a darker, bluish purple. All become plumper, more elastic and less acidic.
How does this happen? One way to understand grape veraison is that it’s a transfer of energy. Grapevines store the energy they create via photosynthesis in their roots. During veraison, that energy moves up the vine to the fruit. As grapes consume it, they develop sugar, aroma compounds and polyphenols, a class of chemical compounds, to protect them from sun damage.
It’s hard to pin down a precise date for this process, as it’s dependent on climatic and other variables. Generally, veraison begins in January in the Southern Hemisphere and in July/August in the Northern Hemisphere.
Those changing colors are a marker for the crucial next stage.
“Veraison can be one of many indicators that harvest is near,” says Stephanie Franklin, founder of Franklin Vines. To determine when to pick, winemakers and vineyard workers monitor “the color of the grape seeds and stems, and the plumpness and sweetness of the grapes, taking samples of the sugar, pH and acid levels,” she says.
The time between grape veraison and harvest fluctuates due to variety, vineyard site, canopy size and other factors. There may be a shorter duration for Merlot grapes than Cabernet Sauvignon, for example, because the latter requires more heat accumulation to ripen before they can be harvested. Still, grape veraison is a useful event for everyone in the vineyard and winery.
“It gives an indication that harvest is 45 to 60 days away,” says Clifton.