phenols are a group of volatile aromatic compounds, consisting of a hydroxyl group bonded with an aromatic hydrocarbon group, that give many of the most pungent spirits their characteristic flavor. They perform a number of functions in plants, only one of which is relevant for our purposes: the bitterness they impart discourages feeding by animals (it can even be toxic to insects). In distilled spirits, these useful compounds, when present as congeners, barrel extracts, or components of added botanicals, impart various woody and smoky aromas and flavors. See botanical; congeners; and maturation.
As congeners, phenols are most prominent in Islay scotch whiskies, to which (smoke-derived) guaiacal, furfural, and cresol add the characteristic notes of smoke, and bromophenols (perhaps derived from the island’s peaty water) add iodine and seaweed. But (presumably) cane-derived phenols such as dihydroeugenol also have a significant presence in high-ester, pot still Jamaican rums and in Martinique rums. Other spirits heavily influenced by phenols as congeners include pomace brandies, mescal and tequila, and sauce-aroma baijius. See pomace brandy and sauce-aroma-style baijiu.
Aging spirits in toasted, heated, or burnt wooden barrels draws out numerous polyphenols—molecules consisting of multiple phenols—that contribute a wide variety of flavors. Phenols and polyphenols may oxidize gradually during barrel maturation, thereby producing flavors and aromas including fruit, vanilla, cinnamon (cinnamic acid), almond (benzoic acid and others), tonka bean (coumarin), coffee, smoke (guiaicol and others), pepper, flowers, clove, sawdust, caramel, brown sugar (maltol), walnuts (phenol aldehyde), and molasses.
Trying to understand the complexity of wood and its influence upon spirits (which can include addition, subtraction, and transformation of compounds) can lead to an alphabet soup of names, including other wood phenols such as 4-methylguaiacol (which gives sweet, candy, eugenol, vanilla, leather, spicy, and smoky aromas), 4-propylguaiacol, 4-ethyl 2, 6-dimethyloxyphenol, and other compounds such as phenyl ketones and aldehydes.
Phenol aldehydes (or phenolic aldehydes), such as vanilla, have properties characteristic of both phenols and aldehydes and are sometimes grouped with phenols. Along with other phenol-derived molecules, the variety of compounds that operate under the term “phenols” combine and interact in so many ways as to justify describing tens of thousands of phenolic compounds and interactions, each potentially contributing to the flavors, aromas, and textures of a wood-aged spirit. See Aldehydes.
For botanical-derived phenols, one must look to things such as Italian amari, French apéritifs, aromatic bitters—all of them rich in bitter phenolics—and, of course, gin: juniper berries are particularly rich in polyphenolic flavonoids. See aperitif and digestive; bitters; and gin.
Miller, Gregory H. Whisky Science Cham, Switzerland: Springer, 2019.
Nykänen, Lalli, and Heikki Suomalainen. Aroma of Beer, Wine, and Distilled Alcoholic Beverages. Berlin: Akademie Verlag, 1983.
By: Doug Frost