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Unfortunately sometimes your beer has a ‘bad’ the aroma or taste that can remind of what? For an example, sulfur or bad eggs.

There are many off flavors in beer but only a handful of very common ones. The majority of these off flavors in beer are naturally occurring. Some are even necessary in certain beers and a few are actually characteristic of specialist styles. They become off flavors only when present in high concentrations and when inappropriate for the style.

A common language has been devised to describe beer flavors and brewers throughout the world have agreed on a terminology that is used for beer.  Whether a flavor is regarded as undesirable or not depends upon several factors: the beer style, the sensitivity of the taster, and the consumer’s expectation.

Sources Referenced: Beer Judge Cert. Program (BJCP), Thomas Barnes'Beer Fault Guide
Acetaldehyde- Green Apples flavor/aroma

Acetaldehyde / Apple Like

Detected In: Aroma, flavor.
Tastes/Smells Like: Aldehydic, bready, bruised apples, cidery, fruity, grassy, green apple, green leaves, latex paint (AKA emulsion paint), raw apple skin, “rough.” Sometimes mistaken for cellar-like, musty or sour notes, sweet apple esters and/or acetic sourness (and vice-versa).
Typical Origins: Yeast activity, Microbial contamination.
Beer Flavor Wheel Number: 0150

A flavor and aroma of fresh-cut green apples, which can be compared to grass, green leaves and latex paint. Typically it is reduced to ethanol by the yeast during the secondary fermentation, but oxidation of the finished beer may reverse this process, converting ethanol to acetaldehyde. Acetaldehyde is generally present in green beer or if the beer is prematurely removed from the yeast.

Low levels of acetaldehyde can be present without causing trouble in some styles, like bière de garde. However, she says, the compound can manifest at inappropriately high levels when a brewer pitches too much yeast into the fermentation tank, ferments too quickly, ferments at unacceptably high temperatures, or takes the liquid off the yeast before the acetaldehyde converts to ethanol.
Acidic / Sour - Vinegar like off-flavor

Acidic / Sour

Detected In: Aroma, flavor.
Tastes/Smells Like: Acidic, cidery, lingering sourness, sharp sourness, sour, sour apples, tangy, tart, vinegary.
Typical Origins: Microbial contamination.
Beer Flavor Wheel Number: 0190

Sour and acidic flavors in beer are readily identifiable through the sour aroma and tartness or vinegar like flavors. The two most prevalent souring acids in beer are acetic and lactic acid. Bacterial infection can sometimes be identified by turbidity and ropiness in beer.

The sour aroma can be perceived as bacteria spoilage of putrefaction. Acid stimulates the sides of the tongue; at high acid levels stimulation can be felt all the way down the throat.

Certain yeast strains produce more acid, giving beer a citrus flavor. Lactic acid produced by lactobacillus and pediococcus bacteria can be introduced by low mash temperatures, by airborne infection in open fermenters, and by unsanitized equipment in contact with beer after the kettle boil.
Arm & Hammer Baking Soda

Alkaline / Bitter

Detected In: Flavor, mouthfeel, aftertaste.
Tastes/Smells Like: Biscuity, bitter, caustic, chalky, detergent-like, drying, harsh, line-cleaner, lye, mineral-like, salty, sodium bicarbonate, soapy. Excessive alkalinity might affect perception of hop bitterness and malt character before it becomes obvious on its own.
Typical Origins: Water, process/equipment faults, contamination.
Beer Flavor Wheel Number: 1310

Alkalinity in beer is a direct result of excessively high pH (above 4.6). It is usually due to excessive residual alkalinity in brewing water or due to excessive additions of brewing salts which increase residual alkalinity (e.g., calcium carbonate or magnesium sulfate). Alkaline materials are typically used as brewhouse cleaners and sanitizers (e.g., soap, caustic cleansers). In the bar trade, they are also used to clean the lines of draught dispense systems. If not properly rinsed, they can impart harsh, unpleasant flavors and mouthfeel to beer.

An excessively alkaline (above ~ pH 5.6) mash, or excessively alkaline sparge water promotes the extraction of polyphenols (see Phenols) which cause astringency and chill haze.

Almond / Oxidation, Malt

Detected In: Aroma, flavor
Tastes/Smells Like: Benzaldehyde, bitter almond, marzipan, nutty. Also described as Brazil nuts, hazelnuts or other types of tree nuts. In some cases it can be reminiscent of Playdough™, plastic or cherries.
Typical Origins: Aging, specialty grains, yeast strain.
Beer Flavor Wheel Number: 0224

An occasional off-flavor in beer which arises due to aging. Similar smelling and tasting compounds might arise due to use of brown or toasted malt. Nutty oxidative notes occur when melanoidins, alcohol and oxygen interact reducing volatile molecules such as esters and hop compounds. They often occur with other oxidative notes such as dark fruit or sherry-like aromas and flavors. These compounds might be reduced back into their original form by oxidizing alcohols into aldehydes. Almond aroma is mostly caused by benzaldehyde.

Some strains of yeast produce aldehydes other than acetaldehyde during the initial phases of fermentation, which can result in aromas which are reminiscent of nuts, Playdough™ or plastic.
Alpha Acids - Hop Bitterness

Alpha Acids / Bitter

Detected In: Flavor, mouthfeel
Tastes/Smells Like: Hoppy bitterness. Some hop varieties produce a “clean” bitterness, while others produce a harsher, “coarser” bitterness. Extreme levels of hop bitterness can impart a drying, harsh resinous and/or tongue-coating mouthfeel.
Typical Origins: Hop additions during wort boil. Additions of hop extracts to wort or beer.
Beer Flavor Wheel Number: 1200

Hop bitterness is imparted to beer by isomerization of humulones during wort boil, converting them to soluble iso-humulones. Iso-alpha-acids derived from hop resins. There are 6 different variants and they all differ in relative bitterness. Of these, cohumulones are the most easily isomerized. Hop bitterness in beer is first detected at about 10 IBU. Thereafter, changes in hop bitterness can typically only be detected in changes of +/- 5 IBU. Conventionally, the maximum threshold for perception of hop bitterness is about 100 IBU, although some people might be able to detect higher levels of bitterness.

To some degree, hop bitterness is expected in virtually all beer styles, with the exception of American lagers, Scottish ales and lambics. Extremely high levels of hop bitterness are expected in American pale ales, American stout, Russian imperial stout, IPA and barleywines.
astringency - tea bag like off-flavor

Astringent (Polyphenols) / Tart

Detected In: Mouthfeel, aftertaste
Tastes/Smells Like: Mouth puckering, puckery, tannin-like, tart
Typical Origins: Yeast, microbial contamination, process faults.
Beer Flavor Wheel Number: 1340

Phenols are an enormous family of aromatic alcohols consisting of a benzene ring plus a hydroxyl group and side chains. Technically, they are alcohols. Unlike esters or fusel alcohols, phenols are largely nonvolatile and don’t get converted into other compounds. This means that once they’re in a beer, they tend to remain in it. There is genetic variation in the ability to detect certain phenolic compounds and some people are completely insensitive to them. Astringent flavors tend to be caused when high molecular-weight proteins (from malt) & polyphenols (from husks & hops) complex and begin to precipitate. It is especially noticeable when beer is chilled to 55° F or lower, since cooling accelerates the rate at which the particles bind together.

Balanced low to strong polyphenol (woody, vanilla, oaky) character is expected in wood-aged beers. Subtle peat character is acceptable in Scotch Ale. Harsh or astringent notes are a fault in other styles of beer.
Matt Kenseth celebrates with a burnout on the track after winning the Bank of America 500 NASCAR race at the Charlotte Motor Speedway in Concord, North Carolina on October 15, 2011.

Autolyzed / Sulfury

Detected In: Appearance, aroma, flavor.
Tastes/Smells Like: Bitter, brothy, decaying/rotten yeast, Marmite™, meaty, muddy, soy sauce, Umami (q.v.), Vegemite™, vitamin B, vitamins, “yeast bite.” Ammonia-like, burned rubber, burnt tires, dirty diaper, eraser, ripe cheese, rotten meat, rubber bands or rubbery at extreme concentrations.
Typical Origins: Yeast, Aging.
Beer Flavor Wheel Number: 0725

Autolysis occurs when yeast cells die, weeks or months after they’ve flocculated and dropped to the bottom of the fermenter or conditioning vessel.. Enzymes within the cell rupture the cell walls, literally making it “spill its guts” into the surrounding liquid. Chemically, autolysis allows amino acids, fatty acids, lipids, phosphorus compounds, vitamins (e.g., riboflavin - vitamin B2) and other compounds to get into the beer. Since the enzymes aren’t destroyed when the yeast cell is ruptured, they can degrade other chemicals in the beer, accelerating the process of aging.

Extremely low autolyzed notes, in the form of brothy, meaty or soy sauce notes are acceptable in strong, aged bottle-conditioned beers, especially dark beers such as old ales. Even in these beers, however, high or unpleasant autolyzed character is a fault.
Soapy flavor

Butyric & Caprylic Acids / Fatty Acid, Sulfury

Detected In: Aroma, flavor
Tastes/Smells Like: (Butyric) Baby sick, butyric acid, putrid, rancid/spoiled butter, rancid/spoiled milk, vomit.
(Caprylic) Goaty, soapy, sweaty, tallowy, waxy, vegetable oil.
Typical Origins: Microbial contamination, aging.
Beer Flavor Wheel Number: 0614 / 0611

Butyric and 2-methyl butyric acids are produced by bacterial infections, usually Clostridium ssp., either during wort production or after packaging. Clostridium can also infect sugar syrups used in brewing, as well as sour mashes exposed to aerobic conditions. All butyric compounds produce distinct, pungent unpleasant rancid odors. Flavor and aroma activity of butyric acid compounds is heavily dependent on pH - their flavors are more intense at lower pH levels.

Capric, caproate and caprylic acids are short chain fatty acids believed to be by-products of yeast metabolism, produced during lipid synthesis by the yeast. They are released into wort either due to leakage through ethanol-damaged cell membranes or due to autolysis. Flavor and aroma activity of caprylic, capric and caproate acid compounds are heavily dependent on pH - their flavors are more intense at lower pH levels.

Catty (p-Menthane-8-thiol-3-one) / Hops, Oxidation

Detected In: Aroma, flavor
Tastes/Smells Like: Black currant leaves, “litter box,” oxidized beer, ribes (a genus of flowering plants which includes black currants and gooseberries), tomato plants, tomcat, tomcat urine.
Typical Origins: Aging, hops, contamination of ingredients.
Beer Flavor Wheel Number: 0810

p-Menthane-8-thiol-3-one and similar compounds are produced by some varieties of hops (e.g., Citra™, Strisselspalt). They can also arise during the early phases of beer oxidation. Rarely, catty note can occur when ingredients contaminated with p-Menthane-8-thiol-3-one precursors are used in brewing.

A catty flavor can be avoided by choosing the appropriate hop strain. Using fresh clean malt and hops. Avoiding oxidizing wort or green beer (e.g., avoiding hot side aeration, and not splashing wort or beer during transfer or packaging). And by Storing the beer at the correct cool temperatures.

Beer made with certain strains of hops might naturally have catty notes. As a sign of oxidation, it is a defect in all styles of beer.
band-aid, plaster

Chlorophenol (Phenol) / Baid Aid™

Detected In: Aroma, flavor, mouthfeel.
Tastes/Smells Like: Adhesive tape, antiseptic, Band-Aid™, Chloraseptic™ disinfectant, “hospital-like,” medicinal, mouthwash, plastic, trichlorophenol (TCP), uncured lacquer. In high levels they might have an astringent, drying, numbing, prickly or puckering mouthfeel.
Typical Origins: Process/equipment faults, contamination.
Beer Flavor Wheel Number: 0504

Chlorophenols (e.g., 2,6-dichlorophenol) are a class of phenols (see Phenols); a large family of aromatic alcohols consisting of a benzene ring plus a hydroxyl group and side chains. Chlorophenols are phenols with a chlorine side chain.

Chlorophenols are formed from chemical reactions between alcohol and chlorine-based sanitizers, chlorine or chloramines used to treat water supplies, or water polluted with chlorine compounds. Unlike esters or fusel alcohols, phenols are largely nonvolatile and don’t get converted into other compounds. This means that once they’re in a beer, they tend to remain in it. There is genetic variation in the ability to detect certain phenolic compounds and some people are completely insensitive to them.
butter or butterscotch flavor

Diacetyl (Vicinal Diketones -VDK) / Buttery Flavor

Detected In: Aroma, flavor, mouthfeel.
Tastes/Smells Like: Butter, buttered popcorn, buttery, buttermilk, butterscotch (at higher levels), honey, milky, movie/theater popcorn, toffee, vanilla. Oily, slick or creamy mouthfeel. Can give illusion of fuller body.
Typical Origins: Yeast, microbial contamination.
Beer Flavor Wheel Number: 0620

Vicinal diketones (VDK) consist of diacetyl & pentanedione. Since they are virtually indistinguishable by typical chemical tests, they are grouped together. Both are natural byproducts of fermentation, formed from minor metabolic products produced during the initial stages of yeast growth and fermentation, which leak out of the yeast cells into the beer. The highest concentrations are found in the initial stages of fermentation, during the reabsorbed by yeast in final phases of fermentation and are metabolized to relatively flavorless diol compounds. High temperature fermentation both produces higher levels of VDK, but does an even better job of reducing them as long as the yeast remains active until the end of fermentation.

Low levels of diacetyl are acceptable in Bohemian Pilsner, English Pale Ales, Scottish Ales, English Brown Ales, Brown Porters, Robust Porters, Sweet Stouts, Oatmeal Stouts, Foreign/Extra Stouts, English IPA, and Strong Ales. They are a fault in other styles of beer, especially most lagers.

Low (sub-threshold) levels of diacetyl can give the illusion of richness or body in any beer style, although this is undesirable in thin-bodied beers.
(Dimethyl Sulfide (DMS) / Cooked Vegetables)

Dimethyl Sulfide (DMS) / Cooked Vegetables

Detected In: Aroma, flavor
Tastes/Smells Like: Cooked broccoli, cooked corn, cooked vegetable, corn, celery, cabbage, canned vegetables (e.g., canned asparagus), creamed corn, grainy, green beans, malty, olives, oysters, parsnips, sea vegetable, seaweed, sulfury, sweet corn, tomato juice, tomato sauce, vegetal, worty. Garlic or leeks (in pure form).
Typical Origins: Malt, microbial contamination.
Beer Flavor Wheel Number: 0732

Dimethyl sulfide is a volatile sulfur‐based organic compound which, when present in excessive amounts, contributes to beer a flavor and aroma varying slightly in character with intensity from cooked corn, celery or parsnip like to almost shellfish or oyster like in high concentrations.

The presence of this compound in beer can stem from two sources: bacterial infection of wort, and/or inefficient elimination or inadvertent entrainment of normally occurring DMS during beer processing.

The major source of high levels of DMS is usually attributable to the presence of an infecting bacteria Obesumbacterium Proteus, commonly referred to as “wort bacteria.” This organism, which generates DMS as a metabolic byproduct, is sometimes found either in inadequately sanitized wort receivers or fermenters and associated transfer lines, pumps, sight glasses and CO₂ collection lines, or in trub mixed with, and infecting, collected yeast that is to be subsequently repitched.
Damp earth - beer off-flavor

Earthy or Musty / Sulfury

Detected In: Aroma, flavor
Tastes/Smells Like: Basement/cellar-like, compost, damp basement/cellar, damp soil, dank, earthy, freshly-dug soil, fusty, moldy, mushroom-like, musty, wet basement/cellar. Occasionally described as “beet-like” or “corky” or as “old books” or “packaging materials.”
Typical Origins: Microbial contamination.
Beer Flavor Wheel Number: 0841, 0842

Earthy characteristics are a defect in beer caused by using water contaminated by microorganisms or by contamination with chemicals produced by bacteria which live in cellars and other damp places. The active ingredient is 2-ethyl fenchol and similar compounds.

Musty characteristics are caused by 2,4,6-Tricholoroanisole and other chloroanisoles produced by molds or fungus, as well as compounds such as geosmin. These chemicals are responsible for “cork taint” in wine, but are less commonly found in beer. While black mold can grow in beer, typically these compounds get into beer because of mold which has grown on equipment which has been put away wet or which has been stored in damp, moldy conditions. Mold can also grow on wooden barrels and corks, or can be introduced to beer if bottles are corked using improperly prepared corks. Moldy aromas can also migrate through soft plastic, contaminating hoses or buckets which are left standing on surfaces prone to mold growth (e.g., damp basement floors).

Earthy or musty flavors are never appropriate. Although the BJCP guidelines allow that some commercial examples of bière de garde might have a bit of musty character, this should be due to yeast strain, not due to actual contamination or “corked” notes.
Fruity Esters

Esters (Isoamyl Acetate) / Fruity

Detected In: Aroma, flavor
Tastes/Smells Like: Bubblegum, butter, candy (e.g., Artificial fruit, bubblegum, Circus Peanuts, Froot Loops™, Juicy Fruit™ gum, pear drops, Trix™ cereal), cream, citrusy (e.g., lemon, lime, orange, tangerine), floral (e.g., feijoa, flowery, geranium, jasmine, lavender, perfumy, rose, ylang-ylang), herbal (e.g., pine, sage), honey, plant-like (e.g., “green,” green banana, new-mown hay, parsnip, waxy), soft fruit (e.g., grape, raspberry, strawberry), spicy (e.g., aniseed, cinnamon, wintergreen, liniment), tree fruit (e.g., apple, apricot, cherry, peach, pear), tropical fruit (e.g., banana, canned pineapple, coconut, mango, papaya, passion fruit, pineapple, “tutti-frutti”), “sweet” (aroma only) and/or vinous (e.g., wine-like, rum, sherry). Bitter, solventy or glue-like in very high concentrations.
Typical Origins: Yeast
Beer Flavor Wheel Number: Variable.

Esters formed in beer are aromatic compounds identified as fruity and estery at high levels. At lower levels, esters become part of the overall flavor Profile. Esters are highly aromatic and the aroma is sometimes described as bananalike or grapefruity.

Esters are developed in different ways. Some yeast strains produce more esters than others, and lower pitching rates produce more esters.

Esters are expected low to medium concentrations in American ales and hybrid styles. They can be present in low to high concentrations in Belgian, English & German Ales. Younger, fresher ales will have higher ester concentrations. German wheat and rye beers are noted for isoamyl acetate (banana) esters. Belgian ales often have for bubblegum, tutti-frutti, pineapple & “tropical fruit” notes.

Fusel Alcohols / Higher Alcoholic

Detected In: Aroma, flavor, mouthfeel
Tastes/Smells Like: Alcoholic, “harsh,” solventy, spicy or vinous in flavor and aroma, sometimes reminiscent of cheap distilled liquors (e.g., cheap vodka or rum). Some fusel alcohols might have an initial sweetness, but a harsh aftertaste. Fusels are detected in mouthfeel as burning, harsh, hot, numbing or prickly sensations. Can also be detected as a prickliness, warming, pepperiness or pain in the nasal passages.
Typical Origins: Yeast
Beer Flavor Wheel Number: 0110, 0120

Various fusel (“higher”) alcohols are produced as minor respiratory byproducts by yeast during the metabolism of amino acids. Acetate and fusel alcohols can all react chemically with oxoacids to produce esters. Yeast can convert amino acids in the wort into higher alcohols by deamination (i.e., removing amine groups), decarboxylation and reduction. Metabolism or oxidation of hydroxy acids or ketoacids can form higher alcohols. Higher alcohols can be produced from sugars which are converted to acetate and then to higher alcohols.

In well-made beer fusels are usually present in subthreshold concentrations. Distressed or wild yeast might metabolize fatty acids (carried into the wort as trub from the hot and cold break) as a source of oxygen and carbon, producing a greater fraction of long chain alcohols and raising fusels to detectable levels. Likewise, high gravity worts, high fermentation temperatures and high concentrations of alcohol also encourage yeast to produce higher alcohols.

Detectable levels of higher alcohols are always a fault. They are likely to appear in strong beers, especially beers fermented at high temperatures (e.g., Belgian strong ales), but can also appear in poorly-made or inadequately aged Eisbocks or strong ales.
Husky - Grainy

Grainy or Husky

Detected In: Aroma, flavor
Tastes/Smells Like: Cereal husks, Fresh wheat or barley, Grainy, Grape Nuts™, “green,” “green malt,” “harsh,” husky, nutty, raw grain flavor.
Typical Origins: Process/equipment faults, Malt.
Beer Flavor Wheel Number: 0310, 0311

Huskiness and graininess are among the potential flavors that malt and cereal adjuncts can contribute to beer. Grain flavors may constitute part of the flavor band of a given beer and be in harmony with its overall flavor. A grain note in a beer is not necessarily a defect. The flavor is often detectable in commercial beer with a high corn adjunct content. Huskiness, on the other hand, is harsher, unpleasant and always a flavor defect.

Both huskiness and graininess are more likely to be perceived by tasting than by a beer’s aroma bouquet, although staling beer often has a grainy smell. Grainlike flavors in a spoiled beer are usually masked by cardboardy and papery tastes. Both grainy and husky flavors can be sampled by tasting pale malt. Following with crystal or caramel malt points them up even more. The highly kilned, essentially saccharified malts have less raw‐grain character than is experienced in the chewing of brewer’s malt. The longer it is chewed, the more the initial flour like and cereal flavors give way to drier, bitter, mouth‐coating huskiness.

Huskiness is even more evident in the taste of the spent grains after sparging. It is a flavor that the taster will recognize ever after, and one that no brewer would want in the beer.


Detected In: Aroma, flavor
Tastes/Smells Like: Alfalfa, crushed green leaves, fresh grass, grass clippings, green leaves, hay, hedge trimmings, leafy, new-mown hay, sagebrush.
Typical Origins: Aging, aldehydes.
Beer Flavor Wheel Number: 0231

Flavor tones reminiscent of freshly cut grass have been detected in beer, although their presence is not very common. They are best detected by their unmistakable aroma. Barley is a member of the grass family, and thus it is not surprising that grassy flavor tones can arise from grains. Because this effect is uncommon it has not been given much attention. Nevertheless, it clearly arises from unfavorable metabolic activity of various microorganisms and high moisture malt.

Grassy tones are unfavorable and reflect careless brewing practices. The best practical measure for avoiding grassy flavors involves the proper storage of malt, which, like hops, is a perishable product. High temperatures and humid conditions should be avoided. Malt, given time, will absorb moisture until it reaches an equilibrium with its environment. Malt that has been ground will do this very quickly, and is very hard to store without deterioration taking place.

Some strains of English and American hops produce grassy notes when used in large quantities, but such notes are only appropriate at low levels and only in highly hopped beers (e.g., IPA).

Horsey / Fatty Acids, Sulfury

Detected In: Aroma, flavor
Tastes/Smells Like: Barnyard, goaty, horse blanket, horse harness, horse stable, horse sweat, leathery, saddle, sweaty, wet dog, wet fur. Rarely described as bacon, Band-Aid™, burnt beans, burnt plastic, clove-like, creosote, plastic, rancid, rotting vegetation, spicy, smoky or woody.
Typical Origins: Microbial contamination..
Beer Flavor Wheel Number: n/a.

Distinctive aromas and flavors produced by various species of Brettanomyces and Dekkera yeast, usually B. Bruxellensis, but also B. Lambicus and B. Clausenii . The active chemicals are primarily 4-ethyl phenol (4-EP) and 4-ethyl guaiacol (4-EG), but also isovaleric acid, guaiacol, 4-ethyl phenol, 2-phenyl ethanol, β-damascenone, isoamyl alcohol, ethyl decanoate, cis-2-nonenal and trans-2-nonenal. On its own, 4-EP produces medicinal phenolic aromas and flavors, while 4-EG produces smoky, bacony or spicy notes.

Some degree of brett character is expected in Lambics. Extremely low levels are permissible as a point of complexity in dry stout and old ales, but such character shouldn’t be obvious. Historically, until the 1950s, Brett strains were present in the yeast blends British brewers used to pitch their wort. So more or less prominent Brett character might be expected in historical recreations of aged English beers, such as 18th or 19th century “stale, vatted” porter, 19th and early 20th century English IPA, and 19th and early 20th century aged “Burton” ales (what the BJCP calls English Barleywine, as well as certain varieties of English Pale Ale and Old Ale).

Barnyard flavor

Indole / Sulfur

Detected In: Aroma, flavor
Tastes/Smells Like: Barnyard, coliform, enteric, fecal, pig-like, and a variety of much more descriptive, but less polite, terms. Some people perceive it as a floral (jasmine) aroma, especially at low levels.
Typical Origins: Microbial contamination..
Beer Flavor Wheel Number: n/a.

While indole and similar compounds naturally occur at trivial levels in beer, due to the thermal decomposition of the amino acid trypophan, “enteric” notes only appear in detectable levels as a result of coliform bacteria (Escherichia Coli spp.) infection. These bacteria metabolize tryptophan to produce a family of chemicals called indoles as well as DMS. Since coliform bacteria are naturally found in the guts of most animals, indole is one of the major components in the smell of feces.

In beer, detectable indole aroma is a sign of serious contamination by coliform bacteria, which can occur when fermentation is slow to start and the wort becomes infected. It can also occur when brewing operations take place close to sources of coliform bacteria (toilet facilities). Rarely, it might be due to use of adjunct sugar syrups which have been spoiled by E. coli infection

Lambic brewers attempting true wild fermentations might occasionally run into problems with E. coli, however, since coliform bacteria are the first “wave” of microflora to colonize the wort during spontaneous fermentation. For this reason, “enteric” aroma and flavor is described as an “unfavorable” characteristic for lambics.
Iodine Solution

Iodoform / Phenol

Detected In: Aroma, flavor.
Tastes/Smells Like: Bitter, hospital-like, Iodophor™, iodine, metallic, sweet.
Typical Origins: Contamination.
Beer Flavor Wheel Number: 0505

Iodoform is an organoiodine compound with the formula CHI3. It has a distinct pungent aroma and a medicinal, sweetish taste. Despite the fact that it isn’t a phenol, the Meilgaard Beer Flavor Wheel classes it, and similar iodine bearing organic chemicals, with the Phenol flavors.

Iodoform notes in beer arise when iodine-based sanitizer isn’t properly rinsed from brewing equipment, or brewery equipment or packaging materials sanitized with “no rinse” iodine cleansers (e.g., Iodophor™) isn’t allowed to dry. Rarely, iodoform notes can arise in beer when wort samples used treated with iodine, used to test mash conversion, are returned to the mash.

Iodoform characteristics can best be avoided by using iodine-based sanitizers in the proper concentrations - more isn’t always better. Thoroughly rinsing any sanitizer from equipment or packaging, or allow “no rinse” sanitizers to thoroughly dry before using equipment. Discard all wort samples that have been tested with iodine rather than returning them to the mash.

Isovaleric Acid / Cheesy

Detected In: Aroma, flavor
Tastes/Smells Like: Blue cheese, cheesy, hydrolytic rancidity, old hops, rancid, Rochefort cheese. Less commonly described as dirty laundry, dirty socks, goaty, putrid, stale cheese, stinky feet, or sweaty.
Typical Origins: Hops, aging, process faults.
Beer Flavor Wheel Number: 0613

Caused by oxidation of alpha acids in hops, usually during storage, which produces valeric, butyric and 2-methyl butyric acids. All of these produce distinctive “blue cheese” notes. Somewhat related to Caprylic (q.v.). Often accompanied by Grassy (q.v.) notes. The intensity of this characteristic decreases with time, both in aged hops and beer made with aged hops. Cheesy notes can also be produced by bacterial infections.

Best ways to avoid cheesy characteristics is by using the freshest hops possible. Store the hops in vacuum-sealed, oxygen-free containers at low temperatures. Badly treated hop cones will often be papery and pale, with no residual greenness. Badly treated pellets or plugs will lose their greenness and might be brown or buff colored. In all cases, they will have significantly less aroma than they would if fresh. If the beer is allowed to age; cheesy notes will recede with time.

Isovaleric notes are never appropriate. While “suranne” (literally, “superannuated”) hops are used in lambics, these should be aged for long enough that any cheesy notes are long gone.
Lightstruck (Sulfury) / Skunky

Lightstruck (Sulfury) / Skunky

Detected In: Aroma, flavor
Tastes/Smells Like: Catty, farty, fecal, mercaptan, polecat, skunky, sulfury, sunstruck. Inaccurately described as methane or natural gas.
Typical Origins: Mishandling.
Beer Flavor Wheel Number: 0724

Light‐struck is an olfactory‐based taste perception, having the characteristic smell of a skunk. It is in the sulfury area of the taste classifications. The major constituent is the sulfur compound, 3‐ methyl‐2‐butene‐1‐thiol.

The light‐struck or sun‐struck flavor also is related in some cases, to the hoppiness, especially in those European imports in green bottles that have been exposed to fluorescent light. Sunlight has a very deleterious effect on beer, a fact brewers have known for well over a hundred years. This comes mostly from altering the hop flavors to sulfury compounds., Beer in clear glass bottles is most affected by sunlight, though beer in green glass bottles is also susceptible. It has been found that fluorescent light is perhaps even more damaging than sunlight. Amber‐brown bottles are the best protection against light damage. One rarely sees green bottles in Europe, and one never sees clear bottles there.

Lightstruck character is never appropriate. Sadly, it is so common in mishandled, badly-packaged, imported European and Mexican “green bottle” beers, especially light lagers, that many people believe that the beers were intentionally brewed that way!
rotten vegetables

Mercaptan (Sulfury) / Rotton Vegetables

Detected In: Aroma, flavor
Tastes/Smells Like: Catty, drains, farty, fecal, leeks, polecat, rotten vegetables, skunky, sulfury, sunstruck. Inaccurately described as methane or natural gas.
Typical Origins: Yeast, microbial contamination.
Beer Flavor Wheel Number: 0722

Caused by chemicals such as ethanethiol, methanethiol, methyl mercaptan, which are typically formed at low levels by some strains of yeast during fermentation. These compounds are produced in detectable quantities by infection by anaerobic bacteria such as Pectinatus frisingensis, P. cerevisiiphilus and Megasphaera Cerevisiae, usually in conjunction with other sulfur-bearing compounds such as hydrogen sulfide or dimethyl sulfide.

Mercaptans are also produced during yeast autolysis due to the decomposition of sulfur-bearing amino acids or peptides. Also see DMS, Hydrogen Sulfide and Lightstruck.

Best avoided by practicing proper sanitation processes. And remove beer from yeast cake soon after fermentation stops (i.e., within 2-4weeks).

Mercaptans are never appropriate in beer, although extremely low sulfury notes are permissible in some varieties of beer fermented with sulfur-producing yeast strains.


Detected In: Appearance, aroma, flavor, mouthfeel.
Tastes/Smells Like: Aluminum foil, Bitter, blood-like, bloody, coin-like, coppery, ferrous sulfate, harsh, inky, iron, iron-like, rusty, rusty water, tingling, tin-like or tinny. Metallic ions can cause haze in beer and can affect foam quality.
Typical Origins: Contamination.
Beer Flavor Wheel Number: 1330

While trace amounts of copper, manganese, iron and zinc are necessary for yeast health, detectable levels of metallic ions are rare in beer. When they arise, they are usually due to high levels of metallic ions in brewing liquor or due to ions leached from metallic brewing equipment or brewing supplies such as filter powders or syrups stored in steel cans. Metallic notes might also arise due to products of lipid oxidation, through processes which aren’t fully understood. Metallic ions can also promote the formation of other staling compounds. High levels of some metallic ions can also be toxic to yeast.

Metallic flavor is definitely an undesirable flavor when present at a readily detectable level. At very low levels (trace concentration) it may be tolerable, but well above the threshold level beer becomes undrinkable, and so should be minimized if it cannot be totally eliminated. Metallic flavor adversely affects the drinkability of beer by building up in the mouth.

There is some scientific controversy over whether metallic tastes are properly part of mouthfeel or flavor, and the exact neurological pathways involved in perceiving metallic sensations.
Moldy Bread

Moldy - Musty

Detected In: Aroma, flavor
Tastes/Smells Like: Basement-like, cellar-like, cork taint, damp, damp basement/cellar, dank, dusty, earthy, fusty, moldy, mildew, mushroom-like, musty, wet basement/cellar. Occasionally described as “beet-like” or “corky” or as “old books” or “packaging materials.”
Typical Origins: Contamination.
Beer Flavor Wheel Number: 0840 - 0842

Moldiness is a clearly recognizable flavor. Mild, barely detectable mustiness that develops in a bottled beer is an aging defect caused by a comparatively slight contamination. Where it is pronounced, moldiness‐mustiness is the result of serious fungal contamination. The contamination may be a result of airborne fungi, or from equipment or packaging the beer has contacted.

Molds, like yeast, are fungi. Barley, malt, wort and beer are ideal substrates for the growth of a range of different fungi. Black bread molds, slimes and mildews can all grow in wort or beer. Brewing in a damp or musty environment risks contamination of the cooled wort or fermenting beer by any of a host of airborne fungi.

Secondary fermentation and aging in a moldy smelling cellar risks contamination by reverse passage of atmospheric air through the fermentation lock (sudden cooling) and by contact of the beer with exposed fermenter surfaces. Where the fermenter’s cap or stopper seals against its rim offers a concealed, often moist area for fungal growth.
Cardboard, paper flavor

Oxidation / Papery

Detected In: Aroma, flavor
Tastes/Smells Like: Cardboard, dull, papery, shoe box, stale, wet cardboard. At low levels papery character can be taste or smell “like ball-point pen,” inky, musty, peppery or prickly. Less commonly, it is perceived as smelling like cucumbers, fat, honey, "library," "old people,” orris root, soy sauce or stale bread crumbs. In dark beers it might be detected as “tomato juice” notes.
Typical Origins: Aging, process faults.
Beer Flavor Wheel Number: 0820

Cardboard and papery notes are caused by long-chain aliphatic (non-aromatic) aldehydes (e.g., 2-nonenal). These are produced when lipid compounds naturally found in malt, which are liberated during mashing and wort boil, but initially bound to other molecules, undergo auto-oxidation.

The most notorious compound, 2-nonenal, is detectable at levels above 0.1 μg/l in water. It is responsible for cardboard or papery notes. Some people describe it as smelling like “library” (decaying paper) or “old people.” The latter sensation might be because 2-nonenol is present in human sweat and the human body produces more 2-nonenal as we age!

Obvious papery notes develop in the mid to late stages of aging, especially in light-colored, light-flavored, relatively weak (i.e., below 6% ABV) beers. At low levels, papery notes might be mistaken for one or more of the sensory descriptors listed above. As described for Oxidation, the time needed to develop papery notes depends mostly on how much oxygen is present in the beer and the temperature at which it is stored. Also see Almond, Leathery, Oxidation and Sherry-like.
Fruit Pits, Cherry


Detected In: Appearance, Aroma, flavor, mouthfeel.
Tastes/Smells Like: Bitter, fruit skins, fruit pits, grape seeds, grape skins, husky, oaky, roasted, tannic, tea-like, vanilla or woody. Some have an astringent, drying, numbing, prickly, puckering or rough mouthfeel, sometimes detectable only in the aftertaste. Some spicy phenols can also be detected as a prickliness, warming, pepperiness or pain in the nasal passages. Polyphenols can combine with proteins in beer to form chill (protein) haze.
Typical Origins: Yeast, microbial contamination, process faults.
Beer Flavor Wheel Number: 0500

Phenols are an enormous family of aromatic alcohols consisting of a benzene ring plus a hydroxyl group and side chains. Technically, they are alcohols. Unlike esters or fusel alcohols, phenols are largely nonvolatile and don’t get converted into other compounds.

The most common phenols found in beer are:
  • Flavanoids (AKA Bioflavanoids, Flavanols:) This is a huge family of phenols with ketone-containing compounds which are naturally found in many plants. They have often little aroma. They produce flavors ranging from mildly to intensely bitter. Specific flavanoids relevant to brewing have aromas flavors reminiscent of chocolate, cocoa, coffee, earth, nuts and/or roasted or toasted foods. Some have an astringent, drying mouthfeel or aftertaste.
  • Polyphenols (AKA Tannins): These are phenols composed of two or more benzene rings. They have bitter, husky, oaky or vanilla-like aromas and flavors, also sometimes described as tasting like grape skins or grape seeds. Most also have an astringent, drying or puckering mouthfeel. They commonly occur in woody or husky plant materials.
  • Salt


    Detected In: Flavor
    Tastes/Smells Like: Salty. Can be described as bitter, harsh, mineral-like or sour at low levels. At very low levels it can increase perceptions of sweetness.
    Typical Origins: Water, process faults.
    Beer Flavor Wheel Number: 0150

    Similar to sugar, salt (NaCl, sodium chloride) is one of the six basic tastes (the others are bitter, umani, fat, sweet, and sour). The taste of salt is quite difficult to describe, but everyone is familiar with its taste, and a touch of it on the tongue is very educational. The perception of saltiness is localized in the gustatory receptors at the upper sides of the front of the tongue, to the rear of those for sweetness. The taste of salt is totally imperceptible in normal beer, and anytime it can be detected it constitutes a flaw.

    Saltiness in beer is due to excess sodium ions, usually due to excessive sodium chloride (table salt) additions rather than brewing with naturally salty water. Potassium chloride (a form of potash, also added to “lite” or dietetic salts) can also have a salty character. Salt is also found in trace amounts in malt, but this isn’t a significant source of salt in beer.

    Saltiness is never appropriate. For the styles listed in the BJCP style guidelines. Dortmunder export comes the closest to having detectable levels of salt since the profile for Dortmunder water has 60 ppm. Scottish beer styles come next, since Edinburgh has 55 ppm of sodium. Specialty beers, such as German gose, might have detectable levels of salt, but only at low to medium-low levels.