This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
The following test depends on the chemical difference between coumarin and vanillin, the odorous principles of the two beans. Coumarin is the anhydride of coumaric acid, and on fusion with a caustic alkali yields acetic and salicylic acids, while vanillin is methyl protocatechin aldehyde, and when treated similarly yields protocatechuic acid. The test is performed by evaporating a small quantity of the extract to dryness, and melting the residue with caustic potash. Transfer the fused mass to a test tube, neutralize with hydrochloric acid, and add a few drops of ferric chloride solution. If Tonka be present in the extract, the beautiful violet coloration characteristic of salicylic acid will at once become evident.
A substitute for vanilla extract is made from synthetic vanillin. The vanillin is simply dissolved in diluted alcohol and the solution colored with a little caramel and sweetened perhaps with syrup. The following is a typical formula:
Vanillin........... 1 ounce
Alcohol........... 6 quarts
Water............. 5 quarts
Syrup............. 1 quart
Caramel sufficient to color. An extract so made does not wholly represent the flavor of the bean; while vanillin is the chief flavoring constituent of the bean, there are present other substances which contribute to the flavor; and connoisseurs prefer this combination, the remaining members of which have not yet been made artificially.