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CHARACTERISTICS: Acetaldehyde is the flavor and aroma of green apples. Itcan also taste and smell acetic/cidery.

CHEMISTRY: Formed as a precursor to alcohol by the yeast, or as a product of the oxidation of alcohol to acetic acid.

CAUSES: Yeast metabolism (fresh-cut apples) uses acetaldehyde as a step in the production of alcohol from glucose. This is a fresh, fruity flavor. The second cause is the oxidation of alcohol to acetic acid, whether by oxidation or by acetobacter (gram-negative). This flavor will be more vinegary and less pleasant.

PROCESS: As a product of yeast metabolism, it can be caused by the strain itself or by premature termination of the yeast’s fermentation, such as oxygen depletion, premature flocculation, etc. such that the reaction from glucose to alcohol is stopped at the acetaldehyde stage.

The other causes are oxidation and contamination by acetic acid bacteria. This will occur during splashing when racking quiet beer (non-kraeusened) and bottling.

REMOVAL: Use a good yeast strain that will attenuate the wort properly. Oxygenate the wort at yeast-pitching time. DO NOT splash or oxygenate the wort when racking or bottling. Long lagering periods will also reduce acetaldehyde.

EXAMPLES: Budweiser deliberately manipulates their yeast and process to give 6-8 ppm acetaldehyde in the beer.


CHARACTERISTICS: Both an aroma and a mouth-feel. A hot, spicy flavor detected by the nose as a vinous aroma and by the tongue by a warming sensation in the middle of the tongue. A warming, prickling sensation in the mouth and throat.

CHEMISTRY: The end product from the conversion of glucose into carbon dioxide and ethyl alcohol. Other, higher alcohols can also be present. These are called fusel oils and contribute to vinous aromas and tastes.

CAUSES: A normal reaction desired in beer, alcohol content is a function of the amount of fermentable sugars in the wort, the fermentation temperature, and the yeast strain.

Fusel oil production will be a function of the yeast strain used and the fermentation temperature (higher temperatures give more fusel oils).

PROCESS: Amount and types of fermentables in wort determine content; yeast strain and attenuation characteristics; fermentation temperature determines fusel oil characteristic.

REDUCTION: The amount of alcohol and fusel alcohols should be appropriate for the beer style. Control alcohol by wort start gravity and wort content (avoid large amounts of sugars). Wort should attenuate to about 1/4 of starting gravity.

Control fusel oils by using colder fermentation temperatures.

EXAMPLES: High, lots of fusel oils: Thomas Hardy’s; Moderate fusel oils: British Bitter; Low fusel oils: Pilsner Urquell.


CHARACTERISTICS: Unlike bitterness, astringency is present as a stimulation of the nerve endings throughout the mouth. It is not an aroma. The taste is a puckering, dry, unpleasant situation. It is a very acidic, tannic, tart sensation reminiscent of grape skins.

CAUSES: Bacterial contamination (lactobacillus and acetobacter); added astringency from grains or hops.

PROCESS: Caused by: poor sanitation; excessive hopping; excessive wort attenuation (small dextrin content) giving greater perception of astringent; boiling grains; excessive grain crushing; too high a lauter run-off temperature (170 degrees max); to much run-off in lautering; letting beer sit too long on trub; non-blowoff primary fermentation; alkaline mash or runoff water; too much sulfate, magnesium or iron; excessively high acidity.

REDUCTION: Process changes to eliminate the above. Crack grain properly, watch mash/runoff pH, 170 degrees maximum for lauter runoff water, use blowoff fermentation; good sanitation practice.

EXAMPLES: Young wine and grape skins; blowout from primary fermentation.


CHARACTERISTICS: Generally a desired characteristic of hop use. Bitterness will be tasted on the back of the tongue and the roof of the mouth. One of the four basic tastes.

CAUSES: Hop content and alpha strength; length of hop boil; presence of dark malts, alkaline water.

PROCESS: How long hops are boiled, type of hop, fermentation temperature (high temperature and quick fermentation decrease bitterness), filtration reduces bitterness.

REDUCTION: Lower alpha hops, hops added at stages through boil, filtration,high temperature ferment.

EXAMPLES: Bittering hop extract in water will sensitize you to bitterness.


CHARACTERISTICS: Mouth feel (will feel full). A sensation of viscosity in the mouth.

CHEMISTRY: Caused by polysaccharides (dextrins) in the beer that are unfermentable by the yeast.

CAUSES: Caused by presence of unfermentable sugars or dextrins.

INCREASE: Desired in beer. High-temperature saccharification rest in mash;use of crystal malt and cara-pils malts; use of malto-dextrin, use of lactose.

REDUCTION: Generally not desired. Use of low-temperature saccharification rest in mash, highly-fermentable wort, use of large amounts of corn sugar in wort, long storage, bacterial breakdown, not boiling wort that may have diastase enzymes present.

EXAMPLES: Low: "lite" American beers; High: Samuel Adams


CHARACTERISTICS: Visual clarity in beer contributes to its appeal and increases points given in competitions.

INCREASE: Use of well-flocculating yeast strains; clearing agents such as polyclar, papain, Irish moss, bentonite, gelatin, etc.; filtration; long, vigorous boil and quick chilling; lagering and aging.

DECREASE: Poor, wrong, weak or mutated yeast strains, some ale yeasts, wheat malt, unmalted barley, poor cold break, poor starch conversion in mash, poor malt crush with lots of flour, bacterial contamination, wild yeast contamination, all-malt beer, high protein content due to ineffective proteolytic rest (especially with undermodified malts), tannin present in beer due to excessive or high temperature sparge.

EXAMPLES: Clear - any American commercial beer; Cloudy - wheat beers


CHARACTERISTICS: As appropriate for style. Properly colored beers win more points in competitions.

LIGHTER: Use of pale malts, use of sugar or other starchy adjuncts, filtration.

DARKER: Use of higher-temperature kilned malts, use of crystal malt, use of dark malts, carmelization of the boil, oxygenating hot wort.

EXAMPLES: Light: Coors Light; Amber: Sam Adams; Dark: Celebrator or Guinness.


CHARACTERISTICS: The presence of carbonic acid in beer gives the head and bubbles when the bottle is opened and pressure released. Gives head characteristic. Taste is tart and acidic, increasing with the carbonation. This is especially noticeable on overcarbonated brews. An overall prickly or stimulating mouth feel. Small bubbles are desired, as these will retain both the head and the carbonation for a longer period.

CAUSES: CO2 from the fermentation process or from bacterial action dissolved in the beer gives carbonation.

TOO MUCH: Excessive priming sugars, bacterial contamination, presence of amylase enzymes in bottled beer, iron or calcium oxalate in the water, isomerized hop extract, autolyzed yeast sediment, excessive starch, not boiling extract worts, fusarium mold on barley or in extract, precipitation of excess salts in the bottle.

TOO LITTLE: Poor bottle cap seal, not enough priming sugar, weak or dead yeast culture when bottling (as from long lagering periods).

EXAMPLES: Highly carbonated: Wheat beers; low: English bitters.


CHARACTERISTICS: A butterscotch aroma and taste, and a slickness on the palate. Not desired in excessive quantities.

CAUSES: A normal product of yeast during fermentation, it is re-absorbed during the course of a normal fermentation. Another cause is the gram-positive bacterium Pediococcus cerevisiae and similar strains in cooled beer, young beer, and aging beer. Lactobacillus strains in the mash can also cause this flavor if the mash held at low temperatures (below 131 degrees). Note that the aroma/taste produced by all of these causes is indistinguishable.

CHEMISTRY: One of a family of vicinal diketones. Presence recognized down to 0.05 ppm, but identified at 0.15 ppm.

HIGH RATES FROM PROCESS: Underpitching of yeast; long periods of wort cooling (overnight); contamination from equipment; poor yeast strain; too-soon clearing (fining) of yeast (before it can reabsorb the diacetyl); too long an acid rest in mash; high adjunct ratio in wort; low fermentation temperature; premature lagering; any process that stimulates yeast then immediately removes it from suspension; use of contaminated sediment for re-pitching (bacteria coexists with yeast in the sediment).

REDUCTION: Sanitation, quick wort chilling combined with adequate yeast starter amount (8 ounces of slurry to 5 gallons), adequate time for primary ferment before lagering or fining/filtering, all-malt recipe, higher temperature primary fermentation, pure yeast culture, washing yeast sediment prior to repitching.

EXAMPLES: HIGH: contaminated homebrew; MODERATE: Sam Smith’s Nut Brown Ale, Pete’s Wicked Ale.


CHARACTERISTICS: Volatile sulfur-based compounds that can give beer a taste and aroma of cooked corn, celery, cabbage or parsnip to almost oystery-shellfish-like in high concentrations. These include dimethyl sulfide (DMS), diethyl sulfide, and di-isopropyl sulfide. DMS is first perceived in aroma at around 30 ppb, and the other compounds at considerably lower concentrations. These compounds are undesirable in beer in high amounts.

CAUSES: Wort bacteria (Obesumbacterium or Hafnia) is a major cause, especially of DMS. Coliform bacteria strains can also give a strong cooked-vegetable note. Additionally, these compounds can be formed during the kilning of green malt and during mashing. DMS is also formed by the yeast in a normal fermentation, and during slow cooling of the wort by a non-microbiological chemical reaction.

HIGH LEVELS DUE TO PROCESS: Poor sanitation (primary cause); not boiling the wort for at least one hour; long cooling times (overnight) before pitching; underpitching; contaminated yeast (especially packet yeast and recovered sediment); high moisture malt; over-sparging with water below 160 degrees.=

REDUCTION: Good sanitation; fresh yeast culture; good one hour or more rolling boil; quick wort cooling; high pitching rates; use of 2-row English malt; proper sparging.

EXAMPLES: Contaminated homebrew.


CHARACTERISTICS: Aromatic compounds that are identified as fruity and estery in higher amounts. The flavor and aroma of fruits such as strawberry, grapefruit, banana, raspberry, apple and pear and others can appear in beer due to these esters. Depending on the style, this can be a desired flavor or one totally unsuitable. Ales and high gravity beers are high in fruity-estery content, while pilsners and American lagers are low.

CHEMISTRY: A by-product of fermentation produced by the yeast. Fruity-estery characteristics increase with fermentation temperature.

INCREASE DUE TO PROCESS: Yeast strain used, higher fermentation temperatures, fermenting some lager yeasts at temperatures above 50 degrees, high-gravity wort.

DECREASE DUE TO PROCESS: Yeast strain used, fermenting ales around 60 degrees or less, lagers around 50 degrees or less, lower gravity wort.

EXAMPLES: High: Old Nick Barley Wine; Low: Coors.


CHARACTERISTICS: The aroma and flavor of fresh-cut grass

CHEMISTRY: The aldehyde called Hexenal, which is detectable in concentrations of 0.2 ppm.

INCREASE DUE TO PROCESS: Poor quality malt, poor storage of malt, cracking grains well in advance of brewing

DECREASE DUE TO PROCESS: Good, fresh malt stored under airtight conditions; cracking grains the day you brew or the night before.

EXAMPLES: Fresh-cut grass


CHARACTERISTICS: Good head on the beer when poured, not excessively large or small, Belgian lace on glass, head remains for a long time. Very much desired.

CAUSES: Small bubbles, dextrins, high molecular weight proteins, isohumulones from hops, nitrogen in wort.

GOOD HEAD FROM PROCESS: Use of cara-pils; use of crystal malt; use of malto-dextrin; all-malt beer; good one hour rolling boil to extract the isohumulones from the hops; use of extracts, especially those designed for use with sugar (but using malt instead of sugar); use of wheat malt; adequate protein rest in mash to allow the proteolytic enzymes to break down the large proteins into albumin and smaller fractions and increase the nitrogen; high-temperature saccharification rest; racking to secondary to get beer off sediment; lower temperature fermentation; bottle conditioning.

POOR HEAD FROM PROCESS: Use of fully modified malts; use of underkilned malts; not using a one-hour boil; inadequate protein rest, low-temperature saccharification rest; oversparging; yeast autolysis from long sediment contact; excessive fusel oils; higher temperature fermentation; excessive fatty acids; overboiling of wort; insufficient or deteriorated hops; some finings.

POOR HEAD WHEN SERVING: Soap, detergent or oils on glasses; lip balm, Chapstick or lipstick on lips.

EXAMPLES: HIGH: Wheat beer; LOW: English bitter, especially cask-conditioned.


CHARACTERISTICS: A taste spectrum that includes astringent tastes, cereal or grainy tastes, and husky tastes. Generally the grainy notes may or may not be desirable, depending on the style, but the husky astringent tastes are undesired. Husky-grainy is generally perceived as a taste, although grain notes can be present in the aroma.

CAUSES: Tannins from grain husks causes the astringent huskiness, while the graininess comes from the starches in the barley malt.

INCREASE DUE TO PROCESS: Excessive grain crushing; powdering the malt during crushing; sparge temperature in excess of 170 degrees; excessive sparging; high pH during sparging (above 6.0); boiling grains; improper decoction mashing; improper wetting of grist during mash-in; direct-firing of mash tun without proper stirring; old beer; too many salts in water (sodium, magnesium, sulfate, chloride); iron in water.

DECREASE DUE TO PROCESS: Proper crush; slow mash-in; lautering temperatures between 164-170 degrees; monitoring pH of runoff and adding gypsum to keep pH below 6; proper sparge amounts; temperature controlled or infusion mash; steeping adjunct grains (such as crystal malt added to extract brews) below 170 degrees instead of bringing to boil; water appropriate to style; iron-free water.

EXAMPLES: Grainy (appropriate): Stoneys, many Midwestern regional lagers


CHARACTERISTICS: Skunk odor; unmistakable; smells like a road kill skunk; tastes like it smells. Totally undesirable in beer.

CHEMISTRY: Light will change some of the hop content of the wort to skunklike sulfuric compounds.

HIGH CONTENT: Light-struck fermenter; clear or green glass bottles; sunlight on brown bottles; bar cooler fluorescent lights on green or clear bottles.

REDUCTION OR ELIMINATION: Fermenter shielded from light; brown or opaque bottles opaque to 400-520 nm light wavelengths; isomerized hop extract; storing beer in a cool, dark place.

EXAMPLES: Any green-bottle Eurolager left in sun for 15 minutes. =


CHARACTERISTICS: A harsh, metallic taste noted both on the tip of the tongue and the roof of the mouth. Can be felt throughout the tongue and mouth in large concentrations. Not desired in beer. Also described as tinny or bloodlike.

CHEMISTRY: The ferrous ion (iron) and some organic compounds formed by hydrolysis of cereal lipids in grain, and oxidization of free fatty acids.

HIGH RATE FROM PROCESS: Iron or mild steel in contact with beer; freshly-scrubbed stainless steel that has not been allowed to oxidize; improper filtering material; high iron content in water; poorly processed grain.

REDUCTION: Use of stainless steel; low-iron water; use of citric acid to re-oxidize stainless that has been abrasively cleaned; use of filtering materials that are acid-washed to remove iron; use of fresh, high-quality grain malt.


CHARACTERISTICS: A cellarlike, damp-earth, rank cabbagy or moldy bread odor. Not a common defect in beer.

CAUSES: Fungal contamination.

CAUSES DUE TO PROCESS: Secondary fermentation or transferring beer in a moldy environment, like a cellar. Secondary fermentation or lagering in a moldy cellar where the temperature fluctuates and permits air to be drawn into the carboy. Poor sanitation.

REMEDIES: Only expose beer to the air for transferring in a reasonably clean environment. Moldiness smelled in the air is a good indication of an unacceptable environment. Constant-temperature secondary or lagering environment (to prevent air entering carboy). Good sanitation practice.


CHARACTERISTICS: An aroma of Brazil nuts, hazelnuts, almonds, or slightly sherry-like. Not necessarily a defect, unless excessive or inappropriate for the style.

CAUSES: A product of oxidization or prolonged overheating during aging or after bottling.

CURES: Store beer in a 55 degree or less cellar; prevent oxidization or splashing when bottling or racking.


CHARACTERISTICS: Cardboard, paper, wet paper, sherry-like, rotten fruit, garbage are all characteristics of oxidation, perceived both as an aroma and a flavor.

CAUSES: Oxidation of beer and the alcohol component into fusel alcohols, trans-2-nonenal, acetaldehyde.

HIGH LEVEL: Aeration of beer when transferring or bottling; excessive head space in bottle; poorly functioning air lock; excessive age; high storage temperatures; widely-varying secondary or lagering temperatures; adding tap water to finished beer.

LOW LEVEL: Quiet transfer of beer when siphoning and bottling; flushing out bottles and kegs with CO2 before filling and capping; cool (<55 degree) storage of bottled beer; proper head space in bottle; use of ascorbic acid; good airlock; constant-temperature secondary/lagering; adding only boiled/chilled water to beer after primary fermentation.


CHARACTERISTICS: A hospital-medicine chest flavor and aroma, best detected by its aroma components; caused by phenols. Some phenolic tastes are desired depending on the style. Other descriptions include Band-Aid-like, plasticlike, smoky, clovelike.

HIGH LEVELS DUE TO PROCESS: Yeast strain; chlorophenols in the water; improper rinse of chlorine sanitizers; oversparging; sparging above pH 6.0; sparging above 170 degrees; wild yeast contamination.

LOW LEVELS DUE TO PROCESS: Charcoal filtering of tap water; good healthy yeast strain; proper sparging while monitoring temperature and pH, good rinse of sanitizers or use of non-chlorine sanitizers.

EXAMPLES: Wheat beers have a high amount of the phenol 4-vinyl guaiacol that gives the characteristic clove taste.


CHARACTERISTICS: Salty is one of the four basic tastes. Saltiness will be found on the tongue, to either side just behind the tip. Excessive saltiness is not desired in beer for the most part, but fair quantities will be a characteristic of Dortmunder lagers and Burton ales.

CHEMISTRY: From sodium chloride and magnesium sulfate and other mineral salts.

HIGH LEVEL FROM PROCESS: Excessive addition of Burton salts or table salt or Epsom salts, especially adding these to water already high in mineral salts; water high in sodium chloride or magnesium sulfate.

LOW LEVEL: Use salt-free water; don’t use or use smaller amounts of added salts, especially Burton water salts.

EXAMPLES: High salty mineral content: Bass ale; Dortmunder lagers.

Low: Pilsner Urquell


CHARACTERISTICS: An acetone-like, laquer-thinner-like, pungent, acrid aroma which is followed up by a harsh, burning sensation on the tongue and possibly the back of the throat.

CHEMISTRY: Ethyl acetate in larger quantities (>33 ppm) is the primary cause, either by wild yeast or the yeast strain used. Other compounds may also be present.

HIGH LEVELS DUE TO PROCESS: Wild yeast contamination due to poor sanitation; high fermentation temperature; non-food grade plastic equipment in contact with the beer; open fermenter, especially after high kraeusen subsides; excessive oxygenation of the wort before pitching; oxygen in secondary fermenter.

LOW LEVELS DUE TO PROCESS: Good sanitization of equipment; only food-grade plastic used; cooler fermentation temperatures; proper wort oxygenation; closed fermenter.


CHARACTERISTICS: Another of the basic tastes. This is perceived on the sides of the tongue towards the back of the mouth. At higher levels it can be felt all the way down the throat. Generally in beer this is perceived as a sour aroma and a tartness or vinegarlike aroma. Bacteria contamination sourness can also be perceived as spoilage or putrefaction.

CHEMISTRY: Caused by lactobacillus, pediococcus, acetobacter and some yeast strains.

HIGH CONTENT DUE TO PROCESS: Poor sanitization; bad yeast strain; too much corn sugar; excessive amounts of citric or ascorbic acid; high fermentation temperatures; excessive acid rest; mashing too long; use of wooden spoon in cooled wort or fermentation; storage at warm temperatures; scratched plastic fermenter.

LOW CONTENT DUE TO PROCESS: Good sanitization; stainless steel equipment and spoons; cool fermentation temperatures; cool beer storage; mashing for not more than two hours; glass carboy fermenter.


CHARACTERISTICS: Strong sulfuric aroma and taste reminiscent of rotten eggs(hydrogen sulfide), sulfur dioxide, or yeast. Other descriptions include garlic, burnt rubber, shrimp-like, meaty.

CHEMISTRY: Formed by amino acids methionine and cysteine in the malt and by certain yeast strains and bacteria, notably Zymononas, Pectinatus, and Megasphaera. Also formed by yeast autolysis.

HIGH LEVEL IN PROCESS: Yeast strain; rapid temperature changes to fermenting wort; bacterial contamination; beer left on sediment; wild yeasts; high fermenter back pressure; poor oxygenation of wort at yeast-pitching time; use of metabisulfite in beer; old beer (yeast autolysis).

LOW LEVEL IN PROCESS: Good yeast strain; good sanitation practice; racking off sediment before lagering; cooling lagers no more than 5 degrees per day; cold-pitching lagers; strong, healthy active primary fermentation (scrubs out the gaseous sulfur compounds).


CHARACTERISTICS: One of the four basic tastes, on the tip of the tongue. Desirability dependent on the beer style.

HIGH LEVELS FROM PROCESS: Quick flocculating or low attenuating yeast strain; lack of yeast nutrients in wort; poor ferment due to lack of oxygen, yeast nutrient or other flaws; higher gravity wort with low-alcohol tolerant yeast; addition of crystal malt or licorice; high-temperature mash; addition of dextrin malt or malto-dextrin combined with a quick fermentation; addition of sugar and pasteurization; addition of lactose; premature lagering.