Section in the annual growth cycle the grapevine after this fruit set (see also under BBCH Code ). It is about the ripening of the berries. This begins in the northern hemisphere depending on the grape variety and weather conditions from late July / early August, in the southern hemisphere in January. At this time, the still green and hard berries have reached about half of their final size. With the onset of maturity, they gradually change to a softer, plastic state.
From a certain degree of softness, the color change takes place, in which the berries begin to become light (berry lightening) or to discolour. The poisonous green colour the berries are turning green white in the white wine varieties, White, yellow, yellowgreen, gray, pink, red or purple, with the red wines in blue, violet or black, This does not happen at the same time with all berries, but concerns first those, which in the context of the blossom first fertilized and most exposed to sun and heat.
The dye formation in the red wine varieties is favored mainly by a high light intensity. With the color change, the sugar content in the berries begins to rise rapidly, with the berry sugar being mainly from the assimilating Scroll originates, but can be mobilized with reserves of leaves also from reserves of the wood, then at the expense of a good Holzreife. The maturity-related transformation of the malic acid in sugar molecules also leads to acid degradation and sugar accumulation in the berries. With increasing sugar concentration, the total acidity in the berries steadily decreases, the content of tartaric acid remains roughly the same. The decrease in concentration is initially due to the increase in berry volume, because with increasing sugar concentration increases osmotic Pressure inside the berry, allowing water over the Xylem (Xylem) flows passively into the berries.
The berries increase in volume until the final volume is reached and the grape skin is stretched so that the xylem compound is interrupted and no further water can flow. Without this blockage of the water flow, the sugar molecules that would continue to accumulate via the conductive tissue (phloem) would increase the osmotic pressure in the berry so much that the berries would inevitably burst. The final volume of the berries is reached after about three to four weeks, after which only sugar is stored until fully ripe. In this late maturing period, especially the varietal specific flavorings formed in the berries. This comes with the relatively new term Engustment circumscribed. The one for the vintage optimal state or time in the vegetation cycle is called physiological maturity designated. Since this is not done at the same time for all the grapes of the vineyard, a selective vintage with several passes may be carried out.
Parallel to the phase of Véraison also begins drove maturity that is, the young shoot of grapevines. For the formation of excess sugar in the leaves, their storage in the berries and for a good wood maturity, a sufficient water supply during the growing season is of crucial importance. Water deficiency is indicated by premature yellowing of the lower leaves and may temporarily halt the whole metabolism. at water stress (Dry stress), the vine must keep the guard cells of the leaves as closed as possible in order to lose as little tissue water and escape the Welketod.
With closed guard cells, however, no more carbon dioxide can be absorbed, which is used for sugar production photosynthesis necessary is. The Yellowing phenomena Dry-stressed plants can be interpreted as starvation symptoms, because without carbon dioxide uptake and assimilation, the plant can not maintain its metabolism in the long term. Such dry stress phases always have a negative effect on the balance of pulp and sugar production and thus also the quality of the grapes. The conclusion of the Véraison or the next point in the cycle is called maturation (Maturity).