Solar-cured tobacco, Bastam, Iran Curing and subsequent aging allow for for that slow oxidation and degradation of carotenoids in tobacco leaf. This makes selected compounds from the tobacco leaves and gives a sweet hay, tea, rose oil, or fruity aromatic taste that contributes to your "smoothness" of the smoke. https://broadfar.com/non-combusted-cigarettes-a-safer-alternative-or-just-a-myth/