When is the right time to harvest? When the grapes are ripe, one would say. But this answer raises another question: what do we mean by ripe? Vines normally bus in the early days of April. June sees the start of the flowering period, which lasts about a month. The grapes remain green and the grapes are small, hard and very solid. In June, during the fruit set period the young grapes start to form. In early August veraison begins. At this point the physiology of the plant alters.
From then onwards the vine puts all its efforts into the fruiting body (the grape which holds the seed or pips).
Growth of the shoots stops and the shoots become brown instead of green. Everything is directed towards the bunches of grapes; the grapes become larger and more elastic, starting to colour. The sugars increase rapidly; they are taken from the plant and photosynthesised in the berry. Once it has started the veraison is not at risk from the weather. As in all plants water is the means of transport. If the earth is wet this assists the passage of different substances to the grape. Ripening starts with the veraison of the first grape.
It normally takes about the same time - from 40 to 50 days depending on the climate, variety and the way the vine is trained. The grape becomes softer and the colour becomes more intense. A key factor in ripening is the day length. In the south, for example, the grapes mature later because at this time of year they have less hours of light. As they mature sugar levels gradually increase, with a corresponding decrease in acidity. For fresh, fragrant white wines or for base wine for sparkling wines the choice is made to harvest early because the aim is to achieve a reasonable level of acidity.
For great wines which are to be aged it is better to wait for the maximum sugar level, until the grapes are overripe, when the plant is resting and the grapes begin to dry out, with an increase in sugars and many other substances as the water evaporates.