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