Gary Reineccius, a professor in the department of food science and nutrition at the University of Minnesota, explains.
Natural and artificial flavors are defined for the consumer in the Code of Federal Regulations. A key line from this definition is the following: "¿ a natural flavor is the essential oil, oleoresin, essence or extractive, protein hydrolysate, distillate, or any product of roasting, heating or enzymolysis, which contains the flavoring constituents derived from a spice, fruit or fruit juice, vegetable or vegetable juice, edible yeast, herb, bark, bud, root, leaf or similar plant material, meat, seafood, poultry, eggs, dairy products, or fermentation products thereof, whose significant function in food is flavoring rather than nutritional." Artificial flavors are those that are made from components that do not meet this definition.
The question at hand, however, appears to be less a matter of legal definition than the "real" or practical difference between these two types of flavorings. There is little substantive difference in the chemical compositions of natural and artificial flavorings. They are both made in a laboratory by a trained professional, a "flavorist," who blends appropriate chemicals together in the right proportions. The flavorist uses "natural" chemicals to make natural flavorings and "synthetic" chemicals to make artificial flavorings. The flavorist creating an artificial flavoring must use the same chemicals in his formulation as would be used to make a natural flavoring, however. Otherwise, the flavoring will not have the desired flavor. The distinction in flavorings--natural versus artificial--comes from the source of these identical chemicals and may be likened to saying that an apple sold in a gas station is artificial and one sold from a fruit stand is natural.
This issue is somewhat confusing to the average consumer in part because of other seeming parallels in the world. One can, for example, make a blue dye out of blueberry extract or synthetic pigments. These dyes are very different in chemical composition yet both yield a blue color. Similarly, consider one shirt made from wool and another from nylon. Both are shirts, but they have very different chemical compositions. This diversity of building blocks is not possible in flavorings--one makes a given flavor only by using specific chemicals. Thus, if a consumer purchases an apple beverage that contains an artificial flavor, she will ingest the same primary chemicals that she would take in if she had chosen a naturally flavored apple beverage.
When making a flavor, the flavorist always begins by going to the scientific literature and researching what chemicals nature uses to make the desired flavor. He then selects from the list of flavor components found in, say, real apples, generally simplifying nature¿s list to eliminate those chemicals that make little contribution to taste or are not permitted owing to toxicity. (Nature has no restrictions on using toxic chemicals, whereas the flavorist does.) The flavorist then either chooses chemicals that are natural (isolated from nature as described above) or synthetic chemicals (made by people) to make the flavor.
So is there truly a difference between natural and artificial flavorings? Yes. Artificial flavorings are simpler in composition and potentially safer because only safety-tested components are utilized. Another difference between natural and artificial flavorings is cost. The search for "natural" sources of chemicals often requires that a manufacturer go to great lengths to obtain a given chemical. Natural coconut flavorings, for example, depend on a chemical called massoya lactone. Massoya lactone comes from the bark of the Massoya tree, which grows in Malaysia. Collecting this natural chemical kills the tree because harvesters must remove the bark and extract it to obtain the lactone. Furthermore, the process is costly. This pure natural chemical is identical to the version made in an organic chemist¿s laboratory, yet it is much more expensive than the synthetic alternative. Consumers pay a lot for natural flavorings. But these are in fact no better in quality, nor are they safer, than their cost-effective artificial counterparts.