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