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Here is a list of common off flavors and aromas and potential causes for troubleshooting.

Alcoholic: A warm prickly sensation in the mouth and throat.

  • Increase Fermentable sugars through use of malt or Adjuncts.
  • Healthy and Attenuattive yeast strains
  • Within the general 145-158 degree F range of mashing temperatures the lower mash temperature produce more fermentables, thus more resulting alcohol.
  • Aeration of wort before pitching aids yeast activity.
  • Fusel (solvent-like) alcohols are procuded at high temperatures
  • Age and oxidation will convert some of the ethanol to higher solvent like alcohol.

Bitter: A sensation generally percieved on the back of the tongue, and sometimes roof of the mouth, as with caffeine or hop resin.

  • High: Black and roasted malts and grains
  • High: Great amounts of boiling hops
  • High: Alkaline water can draw out bitter components from grains
  • High: Effective boiling of hops
  • Low: High fermentation temperatures and quick fermentation rates will decrease hop bitterness
  • Filtration can remove some bitterness.

Body: Not a flavor but a sensation of viscosity in the mouth as with thick (full body) and thin (light body)beers.

  • Full: Use of Malto-dextrin, dextrinous malts, lactose, crystal malt, caramel malt, dextrin (CaraPils) Malt
  • Thin: Use of highly fermentable malt
  • Thin: Use of enzymes that break down carbohydrates in mash, fermentation or storage.
  • Full: High Temperature Mash
  • Low: Low Temperature mash
  • Low: Age will reduce body
  • Low: Wild Yeast and bacteria may reduce body by breaking down carbohydrates

Diacetyl: Butter or butterscotch flavor.

  • High Levels: Unhealthy, non-flocculating yeast
  • High Levels: Not enough soluble nitrogen-based yeast nutrient in wort.
  • High Levels: Not enough oxygen in wort when pitching yeast
  • High Levels: Bacterial contamination
  • High/Low: Yeast strain will influence production of diacetyl
  • High Levels: Excessive use of adjuncts such as corn or rice, deficient in amino acid (soluble nitrogen-based nutrients)
  • High Levels: Chilling fermentation too soon
  • High Levels: High-temperature initial fermentation
  • High Levels: Premature fining takes yeast out of suspension too soon
  • Low Levels: Agitated extended fermentation.
  • Low Levels: High temperature during extended fermentation.
  • Low Levels: Kraeusening
  • High levels: Bacteria from equipment.
  • High/Low: Configuration and size of fermenting vessel will influence production.

DMS (dimethylsulfide): Cooked cabbage or sweet cornlike aroma.

  • High Levels: High-moisture malt, especially six row varieties
  • High Levels: bacterial contamination of wort.
  • Low Levels: Use of two row English malt
  • High Levels: Under pitching of yeast.
  • High Levels: Bacterially infected yeast slurry.
  • Low Levels: Longer boil will diminish DMS
  • High Levels: Oversparging at low temperatures (especially lower than 160 degrees
  • High Levels: Bacteria from equipment.
  • High Levels: Introduction of unfiltered co2 produced by fermentation. Bottle priming will produce small amounts.
  • High Levels: Covered pot during boil.

Husky/Grainy (astringent) : Raw grainlike flavor, dry, puckerlike sensation as in grape skins.

  • Alkaline or high sulfate water.
  • Stems and skins of fruit.
  • Six row more than two row malt
  • Oversparging grains
  • Boiling grains
  • Excess trub
  • Poor hot brew (improper boiling)
  • Over milling/grinding
  • High temperature sparge water (over 175 degrees)

Phenolic: Medicinal, band-aidlike, smokey, clovelike, plasticlike.

  • High: Chlorinated (tap) water.
  • Wheat malt (clovelike) or roasted barley/malts (smoky)
  • Oversparging of mash
  • Boiling grains
  • Cleaning compound residue
  • Plastic hoses and gaskets
  • Bacterial and wild yeast contamination.
  • Defective bottle cap linings.

Sour/Acidic: Sensation generaly perceived on the sides of the tongue sort of like with lemonjuice or sour candy.

  • Introduction of lactobacillus, acetobacter and other acid forming bacteria.
  • Too much refined sugar.
  • Addition of citric acid.
  • Excessive ascorbic acid. (Vitamin C)
  • Mashing too long promotes bacterial growth and acid byproducts in mash.
  • Bacteria in wort, fermentation.
  • Excessive fermentation temperatures promotes bacterial growth.
  • Bacteria harbored in scratched surfaces of plastic, glass, stainless, improper welds, valves, spigots, gaskets, discolored plastic.
  • Use of wooden spoon in cooled wort or fermentation.
  • Storage at warm temperatures.
  • Unsanitary bottles or keg.

See Also