Probably the most important event in the calendar of a grapevine is the point at which the grapes start to turn from green to red and begin to ripen and sweeten. This process is known, in French, as veraison. Veraison happens in white grapes as well, but instead of turning red, they tend to become more translucent instead. This process starts to happen in late July in the Northern Hemisphere and late January in the Southern Hemisphere.

What does it mean?

Veraison is when the grape stops producing and accumulating its various acids and starts to work on accumulating sugars instead, making the grapes sweeter and softer. The color changes help to protect the grapes against the effects of sun and wind – anthocyanin and polyphenols are good for plants too! Once veraison has started, the grapes will be ready to harvest from 30 to 70 days afterwards.

Before veraison starts, wine grapes are small and acidic, green and hard; the green color comes from the pigment chlorophyll. Once ripening starts, the vine moves its energy stores from its roots into its grapes and the chlorophyll is replaced by anthocyanins in the case of red grapes and carotenoids in white grapes, as well as by sugars and other compounds. The grapes also grow – sometimes doubling in size – and develop their aroma compounds, while the acid levels drop. Sugars rise, acids drop and it’s down to the skill of the producer to decide when the perfect balance is struck.

Regional differences

In cooler areas of the world, growers sometimes trim some bunches away from each vine so the bunches left behind get more of the sugars and nutrients.

In warmer regions, some growers trim off leaves to slow down the ripening process so that it occurs later in the year when it’s not so hot.

Some grapes ripen unevenly

There are some varieties of grape that ripen unevenly. Some varieties will have bunches that sport ripe and unripe grapes, not just vines! This uneven ripening is called millerandage and it can make for sweet-smelling but unbalanced and “green” wines. The most commonly-known uneven grapes are Malbec, Zinfandel and Pinot Noir, which is why these are considered to be tricky grapes to grow.