The Flavor–Chemistry Association

Sources of Volatile Aromatic Congeners in Whiskey

“…It is said that Irish Christian monks obtained the secrets of distilling from the Moors of Spain during their voyages to the Mediterranean in the 11th century [11][12][13]. Initially, the monks produced distilled alcohol based on essential oils and herbs, known as aqua vitae, and used it for medicinal purposes, translating in Gaelic to 'Uisce Beatha' (water of life) [12]. Irish whiskey dates back to 1405 (reported in the Annals of Clonmacnoise), 90 years before its notation in Scotland by monk Friar John Cor in 1494 [13].…”

“…Sulfur compounds can have a positive contribution at low levels but begin to have a negative contribution as their concentration increases [44,61]. For example, so-called grapefruit mercaptans/thiols have a grapefruit juice character at <10 ppm but are sulfurous and rubbery at >10 ppm [12].…”

“…In addition to extracting volatiles from the wash, the distillation process involves a reaction stage during which congeners are formed from precursors or interact with other compounds, most of which are impacted by thermal energy, reflux, and the metal composition of the still [44]. Along with other key considerations of still design, the choice of metal can impact the overall flavor of the new spirit while also aiding in the overall efficiency of the process [11,12,29]. Copper is widely used due to its malleability, ease of cleaning, and ability to conduct heat (it disperses the heat evenly across its surface, creating a more even distillation), but it can also remove many undesirable sulfuric malodors that develop during fermentation, such as mercaptans (cabbage odors) and disulfides (burnt plastic and rotten vegetable odors) [61,101].…”

“…Both the foreshots and feints are then recycled into the following batch of low wines, and the process is repeated. This gives the final product a more intense taste, as it allows additional congeners to come through and ensures waste is minimized [12]. Most whiskey is double distilled, i.e., the wash still is followed by the spirit still; however, some whiskey is triple distilled, which is more common in Irish whiskey.…”

“…The angle of the lyne arm can affect the overall flavor; an upwardly sloping arm undergoes the most reflux, resulting in a lighter spirit (less congeners and higher purity of ethanol) [102]. A downwardly sloping arm will produce a heavier spirit, lower in ethanol but with more congeners [7,11,12]. Wash carryover will also be more pronounced with a downwardly sloping arm, sometimes indicated by a higher abundance of furans and pyrazines [33].…”