During summer, a Bourgogne vineyard undergoes one of the most visible changes of the growing season. The small, firm green grapes begin to soften. Pinot Noir gradually turns from green to red and then dark purple, while Chardonnay becomes more translucent and develops a yellow-golden hue. This stage is called véraison. More importantly than the change in colour, it marks the beginning of the grape’s final ripening phase. Before véraison, grapes are hard, green and highly acidic. Their sugar content is low and they are physiologically far from the fruit that will eventually enter the winery. Once véraison begins, the metabolism of the berry changes considerably. The grapes soften and increase in volume, while sugars produced through photosynthesis accumulate in the berries. At the same time, acidity begins to fall.
For Pinot Noir, anthocyanins start accumulating in the skins, creating the characteristic red-purple colour. Chardonnay contains very little anthocyanin, so its transformation is less dramatic: the berries gradually change from opaque green to softer, more translucent shades of green and yellow. A vineyard does not change overnight. Individual berries – even berries within the same bunch – enter véraison at different times. For a period, a Pinot Noir vineyard can therefore contain a mixture of green, pink, red and purple grapes.
From véraison towards harvest
Véraison is an important reference point in the vineyard calendar because the period that follows determines much of the final composition of the grapes. Sugar continues to accumulate while concentrations of important organic acids, particularly malic acid, decrease. Aromatic compounds develop, skins change and seeds gradually mature. For Pinot Noir, the development of tannins and other phenolic compounds becomes especially important.
Warm, dry conditions can accelerate ripening, while cooler weather slows the process. Water availability, canopy health, crop load and the characteristics of the individual vineyard all influence how quickly the grapes progress. This is one reason neighbouring Bourgogne parcels can reach maturity at different times – and why harvest dates cannot simply be decided according to the calendar.
Measuring sugar with a refractometer
As harvest approaches, growers increasingly sample grapes from different parts of the vineyard. Tasting remains essential, but ripeness can also be measured. One of the most practical instruments is the refractometer. A grape is crushed and a few drops of juice are placed onto the instrument. Light passing through the juice is refracted according to the concentration of dissolved substances, of which sugars are by far the most important in grape must. The refractometer translates this into a reading that can be expressed on scales such as Brix or as potential alcohol. It allows a grower to take a grape from the vineyard and obtain a sugar reading within seconds.
Repeated measurements are more informative than a single number. By sampling the same parcel regularly, the grower can follow the progression of sugar accumulation and compare different vineyards, exposures and sections of a vineyard.
Sugar does not determine harvest on its own
A refractometer is useful, but it cannot tell a winemaker when to harvest. Two grapes with exactly the same sugar concentration can taste remarkably different. Acidity and pH matter, but so do the flavour of the fruit, condition of the skins, maturity of the pips and, particularly for Pinot Noir, the character of the tannins. This broader assessment is often referred to as phenolic or physiological maturity.
The decision becomes even more nuanced in Bourgogne because higher sugar levels eventually translate into higher potential alcohol. Waiting longer may produce riper flavours and tannins, but can simultaneously reduce acidity and increase potential alcohol. Picking earlier can preserve freshness but risks harvesting fruit that has not achieved the desired aromatic or phenolic maturity. There is therefore no universally ideal refractometer reading.
A crucial period in Bourgogne
The weeks between véraison and harvest are among the most important of the entire growing season. A heatwave can accelerate sugar accumulation rapidly. Rain can increase berry size and create disease pressure. Drought can slow or temporarily stop vine activity, while cool nights can help preserve acidity.
Growers consequently spend an increasing amount of time walking, tasting and sampling their vineyards as harvest approaches. Véraison is the visible beginning of this final process. What starts as a few pink Pinot Noir berries or increasingly translucent Chardonnay grapes eventually becomes a question at the heart of every vintage: when has this particular vineyard reached the right balance to be picked?