🌿 Véraison

Véraison is the stage at which grape berries begin to ripen: they soften and start to colour. It comes at the end of phase 2 of berry development and opens phase 3, when the berries expand rapidly and accumulate sugar.

Before véraison, phase 2 is a slow "lag" phase. The berry grows only slowly while energy goes to the seeds, the embryo matures and the seed coat lignifies. According to the AWRI, phase 2 lasts between 7 and 40 days, depending on variety and temperature. It is the most temperature-sensitive stage and is delayed by daytime temperatures below 18 °C or above 35 °C, or night temperatures below 13 °C or above 30 °C. Colour development is also delayed by high temperatures.

After véraison sugar accumulates faster in the following weeks and usually slows later. Potassium, amino acids and phenolic compounds increase and malic acid is broken down. In red varieties anthocyanins begin to accumulate in the skins about two weeks before colour is visible, and tannin levels in the skins are already relatively high at véraison and stay about constant. In white grapes phenolic compounds fall to minimal levels. Bunches removed from the vine before véraison generally do not ripen.

In the IVES observation protocol véraison corresponds to BBCH stage 85, and a berry has completed it when it is soft to the touch. It is assessed either by feeling at least 100 berries (for example 20 berries from each of 5 vines) or by visually estimating the percentage of coloured berries, which is acceptable for comparing years for the same variety at the same site. Observations are best made in the morning, and the date of 50% completion is found by interpolation.