Vanillin, C8H8O3 is one of the constituents that contribute to the distinct flavor and aroma of vanilla.
It’s an organic crystal that forms on the outside of the vanilla bean. Although it does occur naturally, a cured vanilla pod only contains about 2% dry weight of vanillin. The extraction of naturally occurring vanillin is not only expensive, but highly inefficient.
The demand for vanilla flavoring has always outweighed the possible supply. The target markets are the ice-cream and chocolate industries, making up almost 75% of the market. Smaller industries include confections, baked goods, perfume, medicines and cleaning products. In 2001, the annual demand or vanillin was 12,000 tons, but only 1800 tons of natural vanillin was produced. The remaining vanillin was chemically synthesized vanillin .
Although the chemical structure of synthetically produced vanillin and naturally-occurring vanillin are identical, it’s just a cheap alternative for the real thing.
Today, a small amount of synthetic vanillin is made from with lignin wastes, a by-product of the paper/wood pulp industries. However, most of the synthetic vanillin is made from guaiacol, which is a petrochemical precursor.
Now call me fussy, but I do not want to be eating something that is a product of petrochemicals. I put petrochemicals in my car, I use plastics made from petrochemicals, I wear materials made from petrochemicals, but I do NOT want to be eating the stuff.
I can understand why synthetic vanillin is produced – it’s cost-effective and there’s more room for profit. It’s also produced because there’s a supply and demand chain. But I’m willing to pay more for the real deal.
If vanillin is listed as an ingredient, it’s most likely that it’s synthetically made. If the product contained naturally occurring vanillin, they call it vanilla. Suffice to say, that I avoid anything that contains vanillin.
 M. J. W. Dignum, J. Kerlera and R. Verpoorte, Vanilla Production: Technological, Chemical and Biosynthetic Aspects, Food Reviews International, 17 (2): 119–120 (2001)