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Context decides
A hint of fermentation character may suit one style and feel wrong in another.
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Beer quality · Faults
Beer faults explained: when an unusual flavour is a warning — and when it is the style.
Butter, green apple, sweetcorn, vinegar, cardboard and sulfur can all appear in beer. The useful question is not simply “Is that flavour present?” but “Does it belong in this beer, at this level, for this reason?”
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Faults have causes
Fermentation health, boiling, oxygen, microbes, storage and dirty dispense can all leave sensory clues.
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One descriptor is not a diagnosis
Smelling butter or apple is a starting point, not proof of exactly what happened.
Diacetyl: butter or butterscotch
Diacetyl is produced during fermentation and is normally reduced as healthy yeast finishes its work. At higher levels it can smell like melted butter or popcorn and may also come from contaminated draught systems.
Acetaldehyde: green apple
Acetaldehyde is part of normal fermentation on the way to alcohol. If too much remains, the beer can seem like green apple, cut pumpkin or fresh paint.
DMS: sweetcorn
Dimethyl sulfide is often described as canned or creamed corn at high levels. It originates from compounds in malt and is managed through brewing and fermentation practice.
Oxidation: paper, honey or sherry
Oxygen and time can flatten fresh beer or create papery, honeyed, nutty and sherry-like notes. Some aged strong beers tolerate or even integrate oxidative character better than delicate ones.
Acidity and “funk” need context too
Vinegar-like acidity or wild-fermentation aromas can be deliberate in sour and mixed-fermentation beer. In a clean lager, the same clues would usually be unwelcome.
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Put it to work
If this page has done its job, the next glass should make a little more sense.