The stage when grapes ripen and change colour is called ‘veraison’. The colour change marks the beginning of the ripening stage, where grapes change from green to their final colour. This can be red, purple or yellow, depending of course on the grape variety. White grapes – like Chardonnay – gain their translucent skin during veraison.
Veraison usually takes place in summer, the exact time varies by region and grape variety. Temperature and weather play a big role in this. Hotter summers make for a faster ripening process. In some countries, such as Brazil, it even occurs twice a year. There, grape plants do not go into hibernation. On average, veraison occurs about 45 days after the grape plants flower.
More sugars, less acids
During veraison, grapes undergo considerable changes at the biochemical level. They stop growing and start accumulating sugars, making them sweeter. At the same time, acids in the grapes change, making them softer in flavour. Tannins in red grapes also soften. This results in less bitter wines. Visually, veraison is striking because the grapes change colour. In red grapes, the green berries turn red or purple, while in white grapes, the green berries show yellow hues and take on a translucent skin.
Measuring sugar
For winemakers, veraison is an important time. They have to keep a close eye on the grapes to start harvesting exactly on time. Do they pick too early? Then the grapes are not ripe enough and not yet developed well enough (too little sugar, for example). But picking too late results in overripe: too much sugar and loss of freshness. Winemakers do not just rely on their experience or visual perception. A refractometer (also known as a ‘brix meter’) is also used. A kind of glucose meter for grapes, among other things (but also for honey, for example). The device measures the sugar content of the grape, thus determining exactly when the right time to harvest is.