Saffron flavor is characterized by a notable bitterness and a penetrating, hay-like aroma. It arises largely from another sugar-hydrocarbon combination, picrocrocin, which may be up to 4% of the fresh weight of the stigmas, and is probably a defense against insects and other predators. The combination itself is bitter. When the stigmas dry out and their cell structures are damaged, both the drying heat and an enzyme act on picrocrocin to liberate the hydrocarbon portion, which is a volatile terpene called safranal. Drying the saffron stigmas thus moderates the bitterness and develops the aroma. Several chemical relatives of safranal round out the overall aroma.