Veraison is the point during the red grape's growth cycle that the berry turns from green to red, which is when some of the best wine producers remove the green grapes that haven't turned red. The purpose is to create more concentrated and higher quality wines by reducing the yield and ensuring more even ripening at harvest. At the beginning of veraison the grapes are small (just half of their final expected size), hard, and green; very high in acidity; and lack glucose and fructose. Shortly thereafter the grapes gain color, size, and ripeness as acidity diminishes.