Sun-cured tobacco, Bastam, Iran Curing and subsequent aging allow for for that sluggish oxidation and degradation of carotenoids in tobacco leaf. This produces certain compounds during the tobacco leaves and offers a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes to the "smoothness" in the smoke. https://broadfar.com/non-combusted-cigarettes-a-safer-alternative-or-just-a-myth/