The fruit have now reached a stage known as veraison, during which they change colour, as they start to ripen. The olives start losing some of their firmness, while increasing the concentration and quality of their oil. The duration of this process varies from cultivar to cultivar. In some, progress is slow, and oil quality and content peak contemporaneously. In other varietals however, the drupes soften and change colour more rapidly: in these olives, oil quality peaks before the olive has accumulated the highest percentage of oil, because the plant is still physiologically active, and continues to produce fatty compounds. The narrowness of a cultivar’s harvest window is dictated by the amount of oil accumulated, but in general, the drupes should be harvested when olive detachment force decreases, natural fruit drop is in its early stages, and the analytical and sensory composition of the oils are at their best.