Sun-cured tobacco, Bastam, Iran Curing and subsequent ageing let for that gradual oxidation and degradation of carotenoids in tobacco leaf. This generates specific compounds while in the tobacco leaves and provides a sweet hay, tea, rose oil, or fruity aromatic taste that contributes to the "smoothness" of your smoke. https://broadfar.com/heated-tobacco-shaping-a-safer-sustainable-smoking-future/