I am reading a little about alchemical preparation of tinctures, and they are all using heat, maybe not boiling heat, but heat is used, and according to them not only that spirit in plants is not destroyed, but it is actually improved. But they are all capturing the evaporation of solvents, so perhaps that is the trick. Perhaps that is what we are doing wrong in our preparation of food, we are letting the evaporation escape. If that is the case, then cast iron pots which recondense vapors are a good solution for such problem.