After fertilization at flowering, the berries begin to grow very quickly. The acid concentration in the unripe berries rises to a maximum value, then the acid concentration is reduced and the sugar content increases rapidly. At this point, the ripening phase, known as the véraison, begins. This is the period within the annual vegetative cycle of the vine, at which the berries become soft and begin to discolour. The end of the ripening phase, or the peak of maturation, is characterised by an optimum Zuckersugar/acidity ratio (see also physiological ripeness). The time between blossoming and ripening varies greatly from one grape variety to another, which is why we speak of early to late ripening grape varieties. Soil type, climate, weather and the work of the winegrower also have an influence on this. The time of ripening also depends on the microclimate in the vineyard and can also differ for individual clones of the same grape variety. So even in smaller wine-growing areas the same grape variety can produce different results.