Fusel alcohol

What it tastes and smells like

• solvent
• nail varnish
• harsh alcoholic heat
• burning finish

Responsible compound: higher alcohols.

Styles this tends to affect

Not where it belongs — where it is most likely to appear when something has gone wrong.

• American barley wine — A strong malt-dense ale with assertive American hop bitterness and citrus-pine aroma alongside the caramel depth.
• Baltic porter — A strong dark lager descended from exported English porter: deep roast and dark fruit, remarkably smooth for its strength.
• Belgian dark strong ale — The strongest of the Belgian dark ales: raisin, fig and dark caramel over substantial warmth, with a surprisingly dry finish.
• Belgian golden strong ale — Pale, very dry and highly carbonated, with intense pepper and fruit and a strength its lightness completely conceals.
• Bock — A strong, dark, malt-dominated lager with deep bread-crust and toasty character and only enough hop to keep it from being sweet.
• British strong ale — A broad category of strong English ales, malt-led and fruity, sitting between strong bitter and barley wine.
• Doppelbock — Intensely malty strong lager, dense with bread crust, caramel and dark fruit, and remarkably clean for its strength.
• Double IPA — IPA scaled up: more strength, more hops and more bitterness, while staying dry enough to remain drinkable.
• Eisbock — A doppelbock concentrated by partially freezing it and removing the ice, intensifying malt, body and alcohol together.
• English barley wine — The strongest traditional English ale: dense malt, dried fruit and marmalade, built to be kept for years.
• Helles Bock — A pale, strong lager with the body of a bock but a brighter, more hop-balanced character — traditionally a spring beer.
• Imperial stout — The strongest stout: dense, viscous and intensely roasted, with dark fruit, chocolate and substantial alcohol warmth.
• Old ale — A matured English strong ale with dried fruit, treacle and often a trace of oxidative or wild character from age.
• Tripel — A strong pale Belgian ale that is simultaneously rich and dry, with pepper, orchard fruit and a sparkling, deceptive drinkability.
• Wee heavy — A strong, intensely malty Scottish ale with deep caramel and dried fruit and almost no hop presence.
• Weizenbock — A strong wheat beer combining Weissbier yeast character with bock malt depth — banana and clove over dark fruit and bread.

If you are drinking it

A harsh solvent burn in a beer that is not especially strong indicates a hot fermentation. Warming a strong beer slightly in the glass often integrates its alcohol; genuine fusel harshness will not improve.

Not a safety issue. Beer’s alcohol, hop compounds and low pH make it inhospitable to organisms that cause illness.

What causes it

If you are brewing it

• Brewer: Control fermentation temperature actively and measure the beer rather than the room, since active fermentation runs warmer than ambient. (prevents)
• Brewer: Pitch an adequate quantity of viable yeast and oxygenate wort properly before pitching. (prevents)

Where in the process this comes from

Steps that can produce this fault when they go wrong. Each links to what the step is for and how it is controlled.

• Freeze concentration — Concentrate a finished beer by freezing it and removing ice, raising strength and body without further fermentation.
• Pitching — Add yeast to cooled, oxygenated wort at a rate matched to the volume, gravity and fermentation temperature.
• Pressure fermentation — Ferment under applied top pressure to suppress ester and fusel production, allowing warmer and therefore faster fermentation without the flavour penalty.
• Primary fermentation — Convert wort sugars into ethanol, carbon dioxide and the esters, phenols and higher alcohols that give beer much of its character.
• Top fermentation — Ferment warm with Saccharomyces cerevisiae, producing the ester and phenol character that distinguishes ales from lagers.
• Wort oxygenation — Dissolve oxygen into cooled wort before pitching, because yeast needs it to build the cell membranes required for healthy growth.