Fusel oils are the double-faced Janus alcohols that can ruin or enhance whisky’s unique aromatics, body, and flavour complexity.
They are a group of long-chain alcohols with higher-than-water boiling points that manifest as oil after fermentation, and concentrate through distillation. Ethanol, the desirable alcohol in all spirit drinks, evaporates before water at 78.2˚C. The primary fusel alcohols, amyl (60–70 per cent of fusel oils), butanol, and propanol, are insolvent in water, carrying two extra carbon molecules. Odourless, colourless fusel oils have a fetid, offensive smell, and an acrid taste. Small doses make whisky unpalatable and injurious to drinkers’ health.
As the spirits industry arose, distillers found fusel oils contaminated cereal fermentations and distilled spirits, observing considerable variations in residual oil volumes between grain species. First described as phlegm in the…
