In order for a scent to travel through the air into your nose, scent molecules must be in a gaseous state. When you gradually heat a material that contains many different scent molecules, the molecules with a low heat of vaporization will turn into gases before the molecules with a high heat of vaporization do. As it turns out, most of the scents that we know and recognize are mixtures of volatile molecules. As the scent molecules vaporized, they mingled with water vapor molecules, which together rose up in the pot. (The water helped you capture a scent in the mason jar by preventing the nice-smelling material from burning, and by extracting additional volatile scent molecules from the material, which rose up with the water vapor.)