In order to be considered "natural" an ingredient must adhere to the standard that "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."
Anything that does not follow this definition is considered artificial. Quite a mouthful, no?
There is actually a trained professional, known as a "flavorist," who creates these ingredients. What may surprise you is that both natural and artificial flavors are made in a laboratory! That's right - the flavorist actually uses the same chemicals to make natural or artificial flavors.
The difference is that the chemicals are either naturally derived or synthetically created. This is not like the difference between wool and nylon, which are both used for making clothes but are different substances.
At a molecular level, natural and artificial flavors appear to be the same. In fact, there is an argument that artificial flavors are safer. This is because they can be created in their pure form. For natural flavors, the source product (for example, an apple) must be dissolved and filtered, even treated with other chemicals, in order to yield the chemicals for the flavoring. This creates a greater potential for impurities to exist in the flavoring.
It is therefore wise to note that natural and artificial flavorings are both chemical additives used to enhance flavor. If a product indicates that it contains a natural flavor, that does not mean the vendor ground their apples to flavor the product - it means they purchased or extracted a specific set of chemicals and artificially added these to the food to alter the taste.
If you are not concerned with flavorings, then pay less attention to whether the source is natural or artificial, and more attention to the position in the ingredients list. If you want a natural food in the sense that it is something you could produce in your own kitchen, ditch the packages that have any added flavoring other than natural spices.
There are certain red flags to look for in an ingredients list. This is by no means a comprehensive list, but a recommendation based on my own experience with purchasing quality foods. When looking at an ingredients list, examine the beginning (initial ingredients), the middle, and the end of the list.
Here is my list of red flags: