The wonderful summer weather allowed the vines to flower in optimum conditions, resulting in healthy pollen tube growth and accumulation of plant growth regulators. This was followed by a very successful berry set, giving the fruit an excellent head-start to the growing season ahead.
Towards the middle of the summer, the berries go through Growth Phase II, whereby their cells expand rapidly resulting in skins that become elastic, transparent and ready for ripening. The acids develop at this stage too; it is the acids in wine (particularly tartaric acid) that create a juice with poise and balance destined to become a wine.
It is Growth Phase III (veraison) that is most important to growers, because this stage brings about the accumulation of water, nutrients, sugar, phenolics, colour, flavour and aroma compounds within the fruit.
Vines go to the effort of making berries appealing in order to attract seed dispersers, either birds or animals. The same theory applies to vine flowers, which are attractive to pollinators due to their scent and colour. The aroma compounds become more developed at the time that the internal seed (embryo) has reached ripeness and is ready to produce a new plant.
During veraison we can expect to see each variety develop different colour, flavour and aroma compounds. Bacchus, for example, will produce terpenes which impart fruity notes in the resulting wines reminiscent of stone fruit and even tropical characters if berries are exposed to the sun.