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