Essential oils like those of lemon and orange, and concentrated aromatic compounds like vanilla, are to flavor what Klaxon sirens are to sound. Thanks largely to the perfume industry, a huge variety of essences are available, from allspice to wormwood. Some chefs have begun using laboratory-style distillation equipment to derive their own concentrates as well.
But using these powerful ingredients--especially diluting them for taste in food and drink--requires finesse. The oils and the solvents in which they are suspended can be flammable. Not all are safe for human consumption. And in high concentration, essences may smell nothing like they do when used by the discerning chef.