Sunlight-cured tobacco, Bastam, Iran Curing and subsequent getting old allow for the sluggish oxidation and degradation of carotenoids in tobacco leaf. This produces specific compounds from the tobacco leaves and offers a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes on the "smoothness" of your smoke. https://broadfar.com/heated-tobacco-shaping-a-safer-sustainable-smoking-future/