Solar-cured tobacco, Bastam, Iran Curing and subsequent getting old permit for that slow oxidation and degradation of carotenoids in tobacco leaf. This makes specific compounds in the tobacco leaves and offers a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes on the "smoothness" in the smoke. https://broadfar.com/oraco-global-trends-in-heat-not-burn-products/