Sunshine-cured tobacco, Bastam, Iran Curing and subsequent ageing let with the sluggish oxidation and degradation of carotenoids in tobacco leaf. This produces particular compounds while in the tobacco leaves and provides a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes to your "smoothness" of your smoke. https://broadfar.com/non-combusted-cigarettes-a-safer-alternative-or-just-a-myth/