Approximately 400 chemical substances make a whiskey to the noble spirit that it is. Crucial for the flavor-related uniqueness of individual spirits is the concentration of those chemical compounds. And even if whisky always has something mystical in itself, several of its ingredients are anything but mysterious, and can be found not only in the most expensive chemistry laboratories. The best example is vanillin, which everyone knows, who has ever been in a kitchen. Vanilla powder, vanilla sugar and almost any taste of vanilla bases on this very compound. In this article I am therefore going to present both vanillin and its derivative vanillic acid, and hence bring some light into the golden brown liquid. (Image: Joselito Tirados)

Vanillin

“Vanillin” C8H8O3 is known as 4-hydroxy-3-methoxybenzaldehyde according to IUPAC. It is a colorless, vanilla-smelling substance with high solubility in alcohol and ether. Vanillin is one of those compounds, which occur frequently in nature. According to its name, vanilla can be found in vanilla pods in high concentrations. Even in the flowering of black salsify, potatoes and other foods, it is located. Thus, amongst others, the smell of old yellowed paper can be attributed to the formation of vanillin. Chemical basis for this is the oxidation with atmospheric oxygen. Today, for the most part vanillin is obtained by lignin, guaiacol and glyoxylic acid, including the possibility of the fermentative production from ferulic acid and eugenol. The odor threshold of vanillin in water is at 20 – 200 ppb. Each year 10000-14000 tons of vanillin are produced by industry to meet the high demand for perfume, vanilla sugar, pharmaceuticals, or as a brightener in zinc electroplating. In the spirits production vanillin gets into the crude distillate by means of oxidative degradation of ferulic acid – one of several components of lignin. A chemical reaction for detection of vanillin is the reaction with iron (III) chloride. This results in a color change to blue violet.

Vanillic acid

Vanillic acid” C8H8O4 whose proper chemical name is 4-hydroxy-3-methoxy-benzoic acid, is a substance that forms colorless and odorless needles at room temperature. As it occurs in some concentration in whiskey, it is readily soluble in alcohol but poorly in water. As well as vanillin, vanillic acid is obtained by the oxidative reaction of the wood’s lignin during the maturing period. The aldehyde group of a limited amount of vanillin in the spirit reacts by oxidation to the acid typical carboxy group. Measurements showed a ratio of vanillin to vanillic acid of 2:1 in whisky. In the laboratory scale, this acid can be created by the oxidation of vanillin by Ag2O or by gradual oxidation using the oxygen in air. Both variants lead to the formation of the characteristic needles. Naturally, vanillic acid is found in many fruits like strawberries, red currants, plums, etc.

Related posts:

1. Aromatic substances of whisky: Syringaldehyde and Syringa acid
2. Aromatic substances of whisky: Eugenol and Guaiacol
3. Aromatic substances of whisky: Acetic acid and Maltol