Sunlight-cured tobacco, Bastam, Iran Curing and subsequent growing old make it possible for with the slow oxidation and degradation of carotenoids in tobacco leaf. This makes particular compounds from the tobacco leaves and gives a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes into the "smoothness" https://broadfar.com/oraco-global-trends-in-heat-not-burn-products/