Beer off-flavours: how to recognise them, causes and fixes
Does your beer smell of butter, green apple, cardboard or sticking plaster? These are the most common off-flavours in homebrewing: how to recognise them, where they come from and how to avoid them next time.
- Diacetyl
- Acetaldehyde
- DMS (dimethyl sulphide)
- Light-struck
- Oxidation
- Chlorophenols
- Fusel alcohols
- Acetic acid
- Hydrogen sulphide
- Astringency
- Ethyl acetate
- Yeast autolysis
Diacetyl
How to recognise it: Your beer smells of butter or buttered popcorn and feels slightly slick.
Cause: The yeast had too little time to reabsorb the diacetyl at the end of fermentation.
What helps: Do a diacetyl rest near the end of fermentation: leave it a little warmer for two days.
Acetaldehyde
How to recognise it: Your beer smells of green apple or freshly cut pumpkin.
Cause: The beer is too young: the yeast has not finished its work.
What helps: Let it mature on the yeast for longer and only package once fermentation is truly finished.
DMS (dimethyl sulphide)
How to recognise it: Your beer smells of cooked corn or canned vegetables.
Cause: The wort was boiled too briefly or with the lid on, or it cooled too slowly.
What helps: Boil for at least 60 minutes, uncovered and rolling, then chill quickly.
Light-struck
How to recognise it: Your beer smells like a skunk or burnt rubber.
Cause: Light has split hop compounds – usually in green or clear bottles.
What helps: Use brown bottles and store the beer in the dark.
Oxidation
How to recognise it: Your beer tastes of wet cardboard or paper and the hop aroma has gone.
Cause: Oxygen got into the finished beer during transfer or packaging.
What helps: Avoid splashing after fermentation, fill from the bottom with a tube and drink the beer fresh.
Chlorophenols
How to recognise it: Your beer smells of sticking plaster, hospital or mouthwash.
Cause: Chlorine from tap water or cleaning agents has reacted with the malt.
What helps: Treat the brewing water with a Campden tablet or an activated carbon filter and rinse cleaning agents thoroughly.
Fusel alcohols
How to recognise it: Your beer burns in the throat and tastes of solvent, almost like spirits.
Cause: Fermentation was too warm, or too little yeast was pitched.
What helps: Control the fermentation temperature and pitch enough healthy yeast.
Acetic acid
How to recognise it: Your beer smells and tastes of vinegar.
Cause: Acetic acid bacteria have infected the beer, usually together with oxygen.
What helps: Clean and sanitise everything after the boil thoroughly and keep the fermenter sealed.
Hydrogen sulphide
How to recognise it: Your beer smells of rotten eggs.
Cause: Some yeasts, especially lager yeasts, produce sulphur early on. Stressed yeast does as well.
What helps: Patience: with enough time and lagering the smell usually disappears by itself.
Astringency
How to recognise it: Your beer makes your mouth pucker like over-steeped black tea.
Cause: Sparge water that was too hot or a pH that was too high has extracted tannins from the husks.
What helps: Sparge at 78 °C at most and check the mash pH.
Ethyl acetate
How to recognise it: Your beer smells of nail polish remover or glue.
Cause: Stressed yeast from fermenting too warm or too little oxygen at the start.
What helps: Aerate the wort well, pitch enough yeast and ferment cooler.
Yeast autolysis
How to recognise it: Your beer smells of meat stock, soy sauce or rubber.
Cause: The beer sat too long and too warm on dead yeast, and the cells broke down.
What helps: Do not leave the beer warm on the yeast cake for weeks after fermentation.