Sunlight-cured tobacco, Bastam, Iran Curing and subsequent getting older allow for that gradual oxidation and degradation of carotenoids in tobacco leaf. This produces certain compounds in the tobacco leaves and gives a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes to the "smoothness" from the smoke. https://broadfar.com/oraco-global-trends-in-heat-not-burn-products/