"Véraison" means "the onset of ripening" and takes place during the long, hot summer, when the vineyards bask in warmth and light. Bud break has led to blossoms, blossoms have led to tight green buttons that will become grape berries. The air is heavy with the drone of insects and, except for the occasional light breezes that ruffle the leaves, the rows of vines seem to sleep through the days. This, however, is deceptive.
Under the canopy of leaves, the berries swell. The vines have become factories for the conversion of sunlight and water into sugars and acids: véraison. Its success depends on a number of factors which, in turn, are controlled by the vineyard manager, the vintner, and, most importantly, by nature herself. Summer is the season of attentiveness, as the human part of the vineyard concentrates its mind and experience on the vegetative part of the vineyard.
The winemaker and the vineyard manager walk the vineyard, inspecting the growth of the vines. They pay attention to a number of things: general health, the growth of weeds, insect control, disease, and any nutritional deficiencies.
They also inspect the shape of the vines, the "canopy." This is the blanket of leaves under which the grape clusters develop.
Major pruning took place in the winter, when most of the last season's new growth was cut away. A lighter pruning happened in the spring, when any unwanted offshoots from the main vine, called "suckers," are cut away so that they don't take energy from the grape clusters. The winemaker and vineyard manager have a specific vine shape in mind, depending on the type of grape, the type of soil, the degree of slope, sunlight patterns, and the weather. Now each vine is inspected to see whether it helps or hinders the ripening of the grapes. Both help and hindrance can be useful.
If a canopy is too thick sunlight cannot penetrate to the clusters, slowing their development; it diverts moisture and sugars from the grape clusters to the leaves. A canopy that is too thin lets too much light and heat reach the clusters -- even if the grapes escape sunburn, they may still ripen before their sugars and acids are fully developed. Different grape types require different types of canopies to achieve their full ripeness.
In addition, the winemaker takes into account the geographic orientation of the vineyard and may shape the canopy to take advantage of morning sunshine but shade the grapes from the harsher afternoon sun. Canopy management is a craft, but it is also an art as the winemaker uses living vines to create what will, eventually, be premium wine. Wine can never be better than the grapes that make it.
The individual grapes have been changing color. Red varieties shift from green to red; white varieties take on a yellow-green coloration. This is the outward sign of véraison. Not all grapes in a cluster will ripen at the same time. The winemaker, patiently walking the rows, takes note of these color changes, waiting for the moment when the sugars in the grapes are fully developed and the seeds are mature and crunchy. The winemaker may use a refractometer to measure sugar levels and °Brix or titration tests to determine the titratable or total acidity within the grape. The quality of a wine grape is also determined by the tannins in the berry, and the only way to test for these is the simplest and oldest method known: taste.
When the winemaker determines that the grapes have reached their peak, that they are most fit for producing the wine desired, skilled vineyard workers are called in, and the madness and exhilaration of harvest begins.