Heat, can also have the undesired effect, of "cooking off" desirable volatile flavor notes... those most often responsible for the lighter, more aromatic, flavor nuances. This can leave a flatter, more one dimensional, final flavor profile. I have found fruits, florals, and aromatics, to be especially susceptible.Heating up the ejuice causes the nicotine to oxidize at at much faster rate then it would naturally and could possibly make the ejuice taste harsh.. If ethyl alcohol is used by a flavor maker as an extraction method - it is still present in the finished product so leaving the cap off for a day or 2 will allow it to evaporate at a normal pace.