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.