Solar-cured tobacco, Bastam, Iran Curing and subsequent getting old allow for the gradual oxidation and degradation of carotenoids in tobacco leaf. This makes particular compounds from the tobacco leaves and provides a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes towards the "smoothness" on the smoke. https://broadfar.com/non-combusted-cigarettes-a-safer-alternative-or-just-a-myth/