Véraison

Before véraison a grape is hard, green, intensely acidic and photosynthetically active in its own right. After it, the berry behaves as a storage organ.

The change is not gradual across a vineyard: individual berries flip over a few days, and a bunch mid-véraison shows both states side by side.

Berry development follows a double-sigmoid curve: a first growth phase, a lag phase, and a second growth phase that begins at véraison. Véraison is the inflection between the lag and the second phase.

Sugar begins to accumulate in the berry as the vine translocates carbohydrate from the leaves. Simultaneously, malic acid stops accumulating and begins to be respired away.

Anthocyanins begin to be synthesised in the skins of black varieties, which is the visible colour change. White varieties soften and turn translucent gold without an obvious colour shift.

The berry also softens as cell walls change, and it becomes far more attractive to birds and to fungal infection — which is why netting goes up and disease management intensifies from this point.

Uneven véraison across a vineyard is a signal of uneven vine balance or water status, and it complicates the harvest decision because parts of the crop will be at different stages.

It is the reference point for the entire ripening period, and the interval from véraison to harvest is one of the more useful ways to compare seasons and sites.