A few beer faults and their origin – in a nutshell
By Moritz Kallmeyer
Master Brewer of Drayman’s Brewery & Distillery, Silverton Pretoria, January 2003
Abnormal water composition, insufficient boil, excess tannin, excessive or alkaline sparging, insufficient kettle evaporation, hot-side aeration.
Fruity aroma /flavour:
From esters, higher alcohols, acetates of higher alcohols. The consequence of under oxygenation of the pitching yeast, too high fermentation temperature, too low pitching rate, or a deteriorated yeast strain. When unpleasant estery and combined with vegetal aroma and flavour it is from coliform contamination of the wort or yeast culture.
Hafnia protea contamination, probably from tainted yeast culture.
From deteriorated hops (oxidized beta-acids)
Buttery (diacetyl) flavour:
Where it is strong and like rancid butter, from lactic-acid bacteria – significantly Pediococcus. Slight or pleasant diacetyl flavour more often from low pitching rate, under oxygenation, petite mutants in culture yeast, or characteristic of specific yeast strain. Also from beer racked off its primary sediment too early or oxidized in the secondary.
Oxidation from too much air in the bottle headspace; trub carried into / lipids oxidized in the ferment; warm storage mishandling; insufficient boil; when with poor head retention, from lipids in the beer.
Sulfury aroma and flavour:
Too low on fermentation temperature; poor rinsing of sulphur-based sterilant; from wild yeast, Zymomonas or coliform bacteria. May be yeast strain specific, or from autolization of sedimented yeast. Except when from bacterial contamination, may be reduced by aging or by scrubbing with carbon dioxide.
Tinned sweetcorn ( Big Corn Bites) aroma and flavour:
Is characteristic of dimethyl sulphide (dms), from poorly malted barley especially sixrow; high moisture malt; hot wort not chilled quickly enough; coliform bacteria contamination.
From too low Ph (too much acid added); from lactic or acetic acid bacterial contamination.
Medicinal aroma / flavour (Phenolic):
From wild yeast or bacteria; chlorine in the ferment either from water source or improper rinsing of chlorine sterilant; plastic leaching contamination; excess of phenolic material from over sparging or weak wort boil. Accentuated by high fermentation temperatures.
Excessive sparging, hot-side aeration; yeast autolization, excessive or oxidized trub carried over into the ferment.
Disagreeable smell / taste; turbidity, acidity:
Pediococcus or Bacillus contamination of the primary ferment.
Green apple flavour:
From acetaldehyde, the principal volatile acid in beer. From too high a fermentation temperature; yeast strain characteristics; bacterial contamination from the ester Ethyl hexanoate.
Banana aroma / flavour:
Acetates. Yeasts strain characteristics; wild yeast contamination; too high fermentation temperature.
Wort extract too low; excessive mash protein digestion; dextrin-poor extract, from too low conversion temperature.
Poor mash digestion; Insufficient boil; wild yeast; bacteria; oxidation of beer; poor starch conversion in mash.
Excessive sparging; poorly degraded hemicellulose.
Lack of head:
Excessive protein rest; over modified malt; too high on adjunct ratio; lipids in the ferment (excessive sparging or autolized yeast) over-foaming in the ferment, repeated foaming due to rough beer transfers; over-boiling; insufficient or deteriorated hops; contact with oil.
Excess of priming sugars; beer not fermented out before packaging; temperature fluctuation; mishandling; old infected malt; iron in water; wild yeast contamination.
Beer light-struck. Avoid direct sunlight during brewing and in package; reduce headspace.
Rotten egg odour:
Hydrogen sulphide; yeast strain characteristics; fermentation by wild yeast; weak fermentation; in bottled or kegged beer it may be from contamination by Zymomonas bacteria.