Beer faults & off-flavors

Yeast.

? mg/l.

See Esters.

5.2™ mash stabilizer.

unknown.

5.2 is a proprietary blend of phosphate salts (mostly sodium phosphate) sold by Five Star Chemical which claims to reduce mash pH to 5.2 and buffer it at that level regardless of starting pH. Under certain conditions, notably when using highly alkaline water, or if you use excess amounts, it can affect flavor and mouthfeel. Also see Alkaline and Salty.

Yeast activity, Microbial contamination.

5-20 mg/l. At 6-8 g/ml it is perceived as a “fruity” flavor. At higher levels it has a distinctive “green apple” aroma flavor and aroma.

Acetaldehyde is the most important aldehyde (carbonyl compound) in beer, although there are others. Acetaldehyde is found in all beer, although detectable levels are considered to be a defect in most beer styles. * It is typically produced as a precursor to ethanol produced during fermentation: glucose is metabolized into pyruvic acid which is then converted to acetaldehyde and then to ethanol. During fermentation some acetaldehyde escapes from the yeast cell. During the final phases of fermentation, the yeast scavenges free acetaldehyde and finishes converting it. * In young beer orf ermenting wort, acetaldehyde levels range from 20-40 mg/l, decreasing to 8-10 mg/l in finished beer. * Oxidation of finished beer might convert ethanol back into acetaldehyde. In this case, acetaldehyde is usually accompanied by other oxidation and/or age-related defects. * The combination of bacterial action and oxidation can reduce acetaldehyde to acetic acid (vinegar) due to the chemical reaction of ethanol and acetaldehyde. In this case, acetaldehyde is usually accompanied by acetic acid and other contamination defects. This is indicative of infection by Acetomonas, Gluconobacter or Zymomonas species. Some Aldehydes Found in Beer Aldehyde Descriptor Detectable range 3-Methylbutanal Unripe banana 0.01-0.3 Acetaldehyde green apples 2-20 mg/l Benzaldeyde Bitter almonds, burnt almonds, cherries 0.035-3.5 Butyraldehyde melon, varnish 0.03-0.2 Hexanal Bitter, vinous 0.003-0.07 Trans-2-nonenal Papery, cardboard 0.00001-0.002

Microbial contamination.

130 mg/l.

Acetic acid is one of the more common sour (q.v.) tastes found in beer. It naturally occurs at low levels in all beers as a result of yeast activity during fermentation, although detectable levels are considered to be a defect in most beer styles. * Acetic acid is volatile and has a relatively low perception threshold, so it can easily be detected in a beer’s aroma as well as in its flavor. * High levels of acetic acid are caused by oxidation of ethanol by bacteria; most commonly Acetobacter species which produce a white pellicle or film on top of the beer in the conditioning vessel. Acetomonas bacterial infection also produces high levels of acetic acid. These infections produce a slimy, ropy film on top of the beer. Both of these infections take time to develop and can only proceed in the presence of oxygen. Zymomonas bacteria (typically Zymomonas mobilus) also produce acetic acid, along with esters, acetaldehyde and sulfur dioxide. Yeasts of the Kloeckera and Brettanomyces families can also produce acetic acid, in conjunction with other distinctive off-flavors (e.g., leathery, sweaty). Infections by these organisms can occur in anaerobic conditions, usually at ale fermentation temperatures or higher.

Yeast activity, process faults.

? mg/l.

See Solventy.

Bacterial contamination.

? mg/l.

See Acetic (Sour), Lactic (Sour) or Sour.

Yeast activity.

See Ethanol, Fusel Alcohol and Solventy.

Aging, specialty grains, yeast strain.

1 mg/l.

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. Also see Catty, Leathery, Oxidation, Papery and Sherry - like.

Hop additions during wort boil. Additions of hop extracts to wort or beer.

5-7 mg/l, ~5 IBU.

Hop bitterness is imparted to beer by isomerization of humulones during wort boil, converting them to soluble iso-humulones. Alpha acid utilization rates (AKA “Kettle Utilization Rates” or KUR) are determined by original gravity of the wort, alpha acid percentage of the hops, freshness of hops & boil time, to a maximum of about 25-33%. Hop bitterness is measured in terms of International Bitterness Units (IBU) or just Bitterness Units (BU), although this also measures soft hop resins in the beer overstating actual alpha acid concentrations by 5-15%. 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. Despite IBU levels, the character of hop bitterness is somewhat subjective. Cohumulones are said to produce harsher, coarser bitterness than humulones, which are believed to impart a mellower, pleasanter bitterness. Perception of hop bitterness is also influenced by mineral additions, malt selection, alcoholic strength and other aspects of the finished beer. Unlike bitterness from phenolic compounds, hop bitterness is generally described as being “cleaner” and much more pleasant, with much less lingering aftertaste. Perception of hop bitterness is increased by the presence of high concentrations of sulfate and magnesium ions. Sulfate ions also aid in extracting alpha acids from hops. Excessive levels of these ions can impart an unpleasant bitterness and aftertaste on their own, however. While higher (more basic) pH conditions aid in the extraction of alpha a cids, hop resins extracted at lower pH conditions (5.2 pH) is said to give a finer, more balanced bitterness. In addition to providing bitterness, polyphenols and hop resins from hops adsorb to the hot break during boiling, helping it to precipitate. Unfortunately, some isohumulones (isomerized alpha acids) are precipitated with the hot break rather than going into the beer.

Yeast action.

? mg/l.

See Esters.

? mg/l.

See Phenols (Polyphenols), also see Cloudiness.

Yeast, Aging.

Variable depending on beer style and exact chemical.

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. In particular, esterases break down esters, destroying fruity or floral aromas and flavors. Other cellular compounds (notably lipids) increase beer pH increasing perception of hop bitterness and possibly imparting slight alkaline notes. Proteolytic enzymes and lipids degrade beer foam proteins and increase carbohydrate (starch) and protein (“chill”) hazes. Note that flocculated yeast takes a while to die. Freshly flocculated yeast (i.e., a few days to a few weeks old) are mostly dormant and have high levels of internal food reserves (glycogen and the disaccharide trehalose). In this state, “yeast cake” or “yeast slurry,” mostly consisting of healthy flocculated yeast can be reused to ferment another batch of beer. On the other hand, old or unhealthy yeast cells will quickly die and rupture. In aged wild beers, the products of yeast autolysis provide food for subsequent colonies of souring bacteria, such as Acetobacter, Lactobacillus, Pediococcus, as well as wild yeasts such as Brettanomyces. Products such as Marmite™ and Vegemite™ are produced by intentionally inducing yeast autolysis by heating yeast. Their meaty, brothy character comes from glutamaic acid (see Umami). Also see Butyric, Caprylic, Dimethyl Sulfate, Isovaleric, Oxidation, Sulfury, Sulfidic, Sulfitic, Umami and Yeasty.

Process faults.

See Bromophenols or Chlorophenols.

Yeast action.

? mg/l.

See Esters (Isoamyl Acetate)

Bacterial contamination.

? mg/l.

Vegetal.

Hops.

? mg/l.

See Phenols (Flavanoids) and Alpha Acids.

Oxidation.

? mg/l.

See Esters and Oxidation.

Malt.

n/a

Fullness of body is determined by the level of dextrins, proteins and other non-fermentable materials in beer. In thin-bodied beers, the reduced viscosity of the liquid makes it seem more watery, while full-bodied beers are more viscous and seem fuller. Lack of suspended particles and body-forming compounds can also contribute to poor head retention and poor foam stability in thin-bodied beers. Likewise, high levels of those materials aid in foam formation and head retention in fuller beers. Combination of thin body and high carbonation in beers which have been stored for a while, especially in beers which started out with fuller body and lower carbonation levels, is a classic sign of a bacterial or wild yeast infection by a species which consumes dextrins.

Malt.

? mg/l.

See Malt.

Process/Equipment faults, contamination.

1.3 µg/l.

A rather unusual off-characteristic, caused by contamination of brewing ingredients or packaging materials with bromophenols (e.g., 2-bromophenol). These compounds are often found in recycled paper and cardboard, as well as fireproofing materials. Also see Chlorophenols, Iodoform, Phenol, Smoky, Spicy and Vanilla.

Malt, process faults.

? mg/l.

See Malty.

Microbial contamination, aging.

2-3 mg/l.

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

Equipment problems, contamination.

? mg/l.

See Plastic.

Microbial contamination, aging.

4-6 mg/l. Levels of 10+ mg/l produce goaty notes.

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.

Malt, adjunct sugars.

? mg/l.

See Malty or Sweet.

Contamination, Process faults.

? mg/l.

See Phenol or Chlorophenol.

Carbonation.

? mg/l.

See Mouthfeel.

Aging, hops, contamination of ingredients.

15 ng/l.

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. Also see Almond, Leathery, Oxidation, Papery and Sherry - like.

Essential oils, contamination.

n/a.

Celery-like notes in beer are caused by essential oils found in old hops (see Citrusy or Hoppy), spices such as coriander (see Ham-like or Spicy), or produced by wort - spoiling coliform bacteria (also see DMS, Indole, Sulfury and Vegetal).

Poor recipe design.

? mg/l.

See Body, Bitterness, Esters, Malty.

Hops, oxidation.

n/a.

See Butyric and Isovaleric Acid.

Process/equipment faults, contamination.

1-5 µg/l in water, 3-40 µg/l in beer.

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. They 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 non - volatile 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. Also see Bromophenols, Iodoform, Phenol, Smoky, Spicy and Vanilla.

Adjunct sugars, yeast.

n/a.

Beer made with a high proportion (20% or more) of sugar often has a cidery flavor and aroma, which is usually reinforced by thin body. Cidery character might be due to weak or incomplete fermentation caused by insufficient yeast nutrients, which results in higher levels of acetaldehyde.

Hops, fruit or spice additions, yeast.

n/a.

Citrusy notes in beer are caused by Esters and Phenols (q.v.). The more floral and fruity notes are usually produced by esters, while the spicy and herbal notes are typically caused by phenols. Hops, especially modern American, high - alpha acid varieties, contain essential oils, such as b-Selenene, a-Muurolene, Limonene, Limonene-10-ol, Citral, Nerol, l - Cadinene, D-Cadinene and oxidized Myrcene, which are also found in citrus fruits. Some yeast strains can also produce citrusy notes, notably Belgian witbier yeast, which can produce orange-like notes. Belgian witbier, is traditionally flavored with bitter (Curaçao) orange (Citrus Aurantium), which produces herbal, citrusy notes, reminiscent of chamomile. Some American interpretations of the style use sweet orange (AKA Valencia orange), which produces a familiar “orange peel” aroma like that found in Grand Marnier or Triple Sec liqueur, or orange flavoring. Likewise, specialty beers flavored with bitter orange or sweet orange might also have similar flavors and aromas. Regular navel oranges don’t have such strongly flavored peel, and have much thicker pith. This pith contributes bitterness, and possibly ham-like notes, but no orange aroma. Finally, some herbs and spices can produce aromas and flavors which are reminiscent of orange or lemon, notably coriander and melissa (AKA lemon balm). Also see Esters, Ham, Hoppy and Spicy.

n/a.

Haze is cause by tiny particles suspended in beer. There are five types of haze: 1) Biological Haze (AKA Bacterial or Yeast Haze): Caused by suspended microorganisms. 2) Oxidation Haze: Haze formed when protein compounds in beer become oxidized. With sufficient aging, oxidation haze will eventually form in all beer. 3) Pectin Haze: Haze cause by suspended pectin (polysaccharide) from fruit. Only found in fruit beers. 4) Protein Haze (AKA Chill or Tannin Haze): 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. 5) Starch Haze (AKA Permanent Haze): Caused by large molecular weight carbohydrates, including beta-glucans, suspended in beer. To Avoid or Control Cloudiness 1) Filtration: 10-20 micron “trap filtration” removes most sediment & ice crystals. 3-5 micron filter removes dead yeast and most starch and hop particles, giving brilliant clarity. 1 micron filter removes yeast and chill haze particles. 0.65 - 0.5 micron filter removes most bacteria. 0.2 micron filter removes all bacteria. 2) Cold Conditioning: Extended cold - conditioning/lagering time can help yeast flocculate and allows protein or starch particles which come out of solution at lower temperatures to precipitate. Lagering is cold conditioning at ~32 °F for 2 or more weeks. 3) Finings: All finings require at least 50 mg/l calcium in water to work. Most work by electrostatically attracting suspended particles to the particles of fining material, forming larger particles which precipitate more quickly. A) Kettle/Copper Finings: Help coagulate hot break, proteins responsible for protein/chill haze and flavor instability. All work by coagulating proteins. Typical kettle finings are: Irish moss (dried seaweed - Chondrus Crispus - at 50-150 mg/l), ProtoflocTM (added at 30 mg/l), carrageen (a gum used in food production - derived from seaweed), and Whirlfloc TM (20-60 mg/l). All are added at the rate of approximately 1 tsp or tablet/5 gallons in the last 15 minutes of the wort boil. B) Fermenter/Cold Side Finings: Either added to conditioning vessel near the end of conditioning period or added to the cask (for cask-conditioned ales). Used to remove yeast, protein, polyphenol or starch hazes. Fining are often packaged as powders and must be rehydrated using sterilized hot water. They take time to work - at least 25 hours. Common yeast flocculants are isinglass (dried collagen obtained from the dried swim bladders of fish, historically sturgeon or cod, now various fish species from the South China Sea. Added at 1-3.5 mg/l at 42-55 ºF), brewers’ gelatin (added at 60-90 mg/l - not as effective as isinglass), PolyclarTM or PVPP (tiny beads of polyvinyl pyrrolidone - plastic) is a polyphenol binder used to remove chill haze (6-10 g/5 gal). Silica gel is a protein binder used to remove protein haze (usually added at 1-3.5 mg/l). 4) Other Methods: Depending on the type of haze and beer style, other methods might work: A) Biological Haze: Yeast strain (some yeasts don’t flocculate well). Increase conditioning time. Use proper sanitation to avoid bacterial or wild yeast infection. Fine using cold side finings (see above). Use protease enzymes such as papain. B) Oxidation Haze: Avoid aeration of wort & beer, except after pitching yeast. Store beer at cool temp. (32-55 °F). C) Pectin Haze: Don’t expose fruit or fresh fruit juice to temperatures above 170 °F. Add papain or pectinase enzyme as necessary. D) Protein Haze: - Alter Grain Bill: Use malt with lower protein content. Limit the use of protein-rich grains (e.g., wheat, rye, oats). Use adjunct grains to reduce overall protein content of grist. - Use a protein rest (113-131°F). - Avoid Polyphenol/Tannin Extraction. Don’t over-crush grain to avoid getting polyphenol/tannin rich husk particles into wort. Don’t over-sparge mash (i.e., pH above 5.8, S.G. below 1.008). Don’t heat mash above 168 °F. Don’t heat grains or tannin-rich fruits, herbs, spices or vegetables above 168 °F. Recirculate or vorlauf mash runoff until it runs clear to avoid carrying husk particles into copper. - Get a good hot break. Boil wort for at least 1 hour at a rolling boil. Use hot-side finings (see above) - Get good separation of hot break from wort so trub isn’t carried into the fermenter. Commercial breweries sometimes use filtration or a hopback to achieve this. - Quickly cool wort to precipitate cold break. Ideally, temperature should drop from boiling to below 100 °F within 30 minutes. - Get good separation of cold break so trub isn’t carried into fermenter. But, some cold break in the fermenter is necessary for yeast health. - Use cold side finings in the conditioning tank, as described for Biological haze. Papain can break down proteins, but its action is indiscriminate and can affect body and head formation. - Increase cold conditioning time. - Serve beer at temperatures above 55 °F. E) Starch Haze: - Use high-quality malt (lower beta-glucans). - Don’t over-crush grains to avoid getting starch particles into beer. - Use a beta-glucan rest during mashing (110 °F for 15 min.). - Improve mashing technique. Increase mashing time to insure complete starch conversion. Make sure that mash temperature is in the correct range for optimal starch conversion (~143-158 °F). Test for complete starch conversion before mashing out. Recirculate or vorlauf mash runoff until it runs clear (to avoid carrying starch particles into copper). - Some brewers use amylase enzyme in the fermentation or conditioning tank, but this is problematic since amylase will eventually destroy all starches in your beer, not just beta - glucans.

Wood-aging.

? mg/l.

Associated with wood-aged beers, especially those aged in oak casks. Whiskey lactone is a major flavor and aroma in some whiskeys and to a lesser extent in oak-aged beers and other distilled spirits. While the exact origin of whiskey lactone is unknown, it is believed to come from the metabolism of malt-derived compounds by lactic acid bacteria (especially Lactobacillus spp.) during fermentation.

n/a.

n/a.

In every flight of doctored beers, there should be at least one fault-free undoctored beer. For tracking purposes, it is called the control and is sometimes given the tracking number of 0000.

Bacterial contamination.

? mg/l.

See Onion or Vegetal.

Bacterial contamination.

? mg/l.

See Vegetal.

Bacterial contamination.

? mg/l.

Mainly dialkyl sulfides, sulfurous-RSR, methyl thioacetate. See Onion or Vicinal Diketones (VDK).Vegetal.

Grain adjuncts.

? mg/l.

See DMS, Grainy or Malty.

Malt, microbial contamination.

10 - 150 μg/l, 25-50 µg/l in beer.

Dimethyl sulfide (DMS) is a volatile sulfur - based organic compound derived from S-methyl methionine (SMM) which is an amino acid derivative synthesized when grain germinates during malting. No DMS is produced during germination, though. SMM levels depend on barley strain and how the grain is malted; British pale ale malthas the lowest SMM levels, while Pils and 6-row lager malts have the highest levels (up to 8 times that of pale ale malt). Drying and kilning the malt at higher temperatures converts some SMM also drives off some DMS, so darker malts have less DMS than paler malts (e.g., the difference between Pils malt and Munich malt). Adjunct grains such as corn also contain high levels of SMM. SMM is liberated into solution during mashing and is degraded into DMS during wort boiling. The chemical reaction is SMM > Dimethyl Sulfoxide (DMSO) > DMS. Fortunately, DMS is a volatile compound, so it can be driven off during a long, vigorous boil. Since DMS is produced at temperatures below boiling, slow cooling of the wort means that DMS is formed which isn’t boiled away. Vigorous fermentation, especially open fermentation, also helps to drive off DMS. Wild yeast or Zymomonas or Proteus bacteria may produce high enough DMS levels as to make beer undrinkable, but these also produce other off-flavors such as acetic acid, phenols and other sulfur compounds.

Dry hops added in tank or cask.

? mg/l.

See Hoppy.

Astringency, dark malt character, lack of residual sugars.

? mg/l.

See Astringency, Body or Malty.

Microbial contamination.

5 µg/l.

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. Closely related to Musty character (see Musty). The active ingredient is 2-ethyl fenchol and similar compounds. Also see Musty.

Yeast.

0.4-1.6 mg/l. Beer flavor wheel number: n/a. Also see Solventy. Other Esters Ester Description Threshold Butyl acetate Banana, sweet 0.04-0.4 mg/l Ethyl caprate Goaty 0.01-1.0 Ethyl caprylate Apple, sweet, fruity 0.01-1.5 Ethyl dodecanoate Soapy, estery 3.5 Ethyl lactate Fruity, strawberry 250 Ethyl myristate Vegetable oil 0.4 Isoamyl propionate Aniseed, pineapple 0.015 Phenylethyl acetate Apples, honey, roses 0.05-3.8

In beer, esters are formed by the esterification of fatty acids by Ethanol, and also in small amounts by the esterification of Fusel Alcohols. Ester precursors are produced as minor elements of yeast metabolism: Alcohol Acetyl Trans ferase (AAT) and Acetyl Coenzyme A (aCoA ); aCoA is normally used for the synthesis of lipids, which the yeast cell needs to build cell membranes. Esters are formed under conditions when aCoA isn’t needed for synthesizing cell components. So factors which promote yeast growth (e.g., high levels of aeration) lower ester production. Also see Solventy. Esters are mostly produced during the main (fermentation) phase of primary fermentation, but can increase slowly during the late phases of fermentation and during secondary fermentation. During long secondary fermentation, the level of esters might double. Acceptable thresholds for esters in bottom fermented beers are up to 60 mg/l. Top fermented beers can contain up to 80 mg/l of esters. Type and character of esters produced depends on the exact chemical reaction. Perception thresholds vary depending on the exact molecule. While there are about 60 different esters found in beer, the most important are: ethyl acetate, isoamyl acetate, isobutyl acetate, β-phenyl acetate, ethyl hexanoate, and ethyl caprylate. - Ethyl Acetate: The most common ester in beer, most typically described as smelling like ripe apples, pears or pear drops. Typical Concentration in Beer: 5-30 mg/l. Perception

Yeast.

5,000-13,000 mg/l. (About 6% ABV in beer).

Yeast produces ethanol (along with carbon dioxide) as a major product of anaerobic respiration during fermentation. Acetate and various fusel (“higher”) alcohols are produced as minor respiratory byproducts during the metabolism of amino acids. Ethanol, acetate and fusel alcohols can all react chemically with oxoacids to produce esters. Ethanol is detectable at 1.5-2% ABV. Also see Fusel Alcohol and Solventy.

Contamination, additions of oily adjuncts.

?.

This category covers a variety of edible and inedible lipids (waxes, oils, sterols, etc.) and hydrocarbon compounds. They are all very rare in beer. While fat is arguably one of the basic tastes (scientists are still debating over whether there are specific taste receptors for fat or fatty acids), detectably fatty substances (as opposed to fatty acids) don’t naturally occur in beer. Oily or fatty substances in beer are associated with unusual adjuncts added to the beer (e.g., coconut, peanuts) or with accidental contamination of wort, beer or brewing equipment. When evaluating beer, oil on glassware or on your lips can affect head formation and retention.

Yeast activity, infection.

n/a.

See Body and Head Formation

? mg/l.

See Esters.

Yeast.

Variable, usually ~50-200 mg/l. Beer Flavor Wheel Numbers: 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. - Acetate and fusel alcohols can all react chemically with oxoacids to produce esters. Oxidation of beer due to aging can convert fusel alcohols to esters. In well-made beer fusels are usually present in sub - threshold 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. In beer, even if it’s not harsh or unpleasant, strong alcoholic notes are usually due to elevated levels of higher alcohols. Pure ethanol has little aroma or flavor of its own and is mostly detected in mouthfeel. Fusel alcohol concentrations in top-fermented beers should not exceed 100 mg/l. Fusel alcohol concentrations in bottom-fermented beers should not exceed 60 - 90 mg/l. Solventy notes can also be produced by very high levels of ethyl acetate and similar esters (see Esters). While technically alcohols, Phenolic compounds are described in their own sections. Also see Ethanol and Solventy. Alcohols in Beer Alcohol Flavor Detectable range 2-phenylethanol Roses, bitter, perfumed 8-35 4-vinyl guaiacol Clove-like 0.05-0.55 Cis-3-hexen-1-ol Fresh cut grass 0.025 Ethanol Alcoholic, strong <5,000 - 100,000 mg/l Glycerol Sweetish, viscous 1,300-2,000 Isoamyl alcohol Vinous, banana, sweet 30-70 Isobutanol Alcoholic 80-100 n-propanol Alcoholic ~600 Phenol Phenol 0.01-0.05 Propan-1-ol Alcoholic 3-16 Tyrosol Bitter 3-40

Infection.

? mg/l.

See Onion or Sulfury.

Carbonation.

? mg/l.

See Head Formation and Retention.

? mg/l.

See Hoppy.

Process/equipment faults, Malt.

10 µg/l.

Caused by compounds such as isobutyraldehyde which are naturally found in grain husks. As with Polyphenols (see Cloudiness and Phenols) these compounds are extracted from husks due to over-crushing, oversparging, sparging with hot or alkaline water, or excessively long mashes. Higher levels of isobutyraldehyde are found in freshly-made malt which hasn’t had sufficient time to rest (2-8 weeks).

Aging, aldehydes.

15 mg/l.

Caused by various compounds, including the aldehydes hexanal (e.g., cis-3-hexenol), furfuryl octanoate, and heptanal, which are produced by the use of large quantities of hops (especially fresh, undried hops), oxidation of alcohols in the finished beer, and/or the deterioration of improperly stored malt or hops. Certain strains of hops also impart grassy flavors and aromas to beer.

Herb or spice additions.

n/a.

Ham-like aromas are occasionally found in homebrewed interpretations of Belgian witbier, or beers where similar ingredients have been added. These aromas can occur when common or aged coriander is substituted for fresh, Oriental coriander. When this happens, oxidized essential oils can also give rise to soapy or celery-like notes. The chemicals which produce ham-like aromas are furans and, possibly, essential oils such as b-Selenene and Cadinenes.

Yeast, Packaging.

n/a.

Head on beer is formed when pressurized gas, typically carbon dioxide, but sometimes nitrogen (CO 2 or N 2) comes out of solution & interacts with surface-active materials, which form a skin around the gas bubbles, keeping them from escaping into the air. As gas vents from the beer, the foam gradually collapses. More gas means more potential foam. Smaller, more even bubbles produce a longer-lasting, more stable head. Head-Forming Materials: Head forming materials in the beer are short - to medium-chain proteins and starches (dextrins) in the beer, along with appropriate levels of dissolved gas (carbon dioxide or nitrogen) in the beer and sufficient nucleation sites (due to suspended particles of material) to encourage bubble formation. Head Retention: Head retention is due to the factors listed above, as well as alpha acids and larger starch and protein particles in the beer. Head retention is measured in terms of the time required for the head to collapse to half its initial height. It should last at least a minute for in well-made beers. Head texture should be uniform and tight, leaving “lace” on the glass as the beer is consumed. Foam positive substances: The main foam producers are medium-length proteins (10k - 60k molecular weight) and water-soluble gums (e.g., beta-glucans), but also isohumulones and dextrins. Unoxidized tannins and anthocyanogens play a minor role. Increasing viscosity also increases foaming, so beers with fuller body produce more foam. Nitrogen gas aids foam by forming smaller bubbles than CO 2. Higher temperature kilning promotes foam-forming materials in malt. Commercial brewers also use heading agents to promote head production and retention. Foam detrimental substances: Oils, fats, waxes & alcohols are all detrimental to foam production. High levels of amino acids, low molecular weight polypeptides, oxidized tannins & anthocyanogens are also detrimental to foam. Lack of Head Retention: Lack of head retention and/or formation is caused by a number of factors: 1) Presence of Oils: Oils in beer or on the inside of the glass reduces surface tension. This keeps bubbles from forming and breaks down bubbles faster. 2) Lack of proteins. Short-chain polypeptides (proteins) are needed for head formation, while medium length polypeptides are necessary for head stability. 3) Lack of carbonation. Low levels of dissolved carbon dioxide and/or low levels of pressure mean less carbon dioxide to form bubbles. 4) Lack of nucleation points. In order for bubbles to form, there must be places where bubbles can “attach” themselves. In beer, nucleation points can form on the inside of the glass or on suspended material. This iso ne of the reasons why hazy beers tend to form bigger heads than clear beers, especially those which have been highly filtered. 5) Lack of hops. Alpha acids from hops help bubbles to cling together which aids head stability. Suspended hop particles help bubbles form. This explains why hoppy beers, such as pilsners and IPA have bigger, frothier heads than similar beers with less hop bitterness. 6) Lack of dextrins and starches. Starches aid foam stability. This is the reason that beers with high levels of starches, such as wheat beers, form bigger heads. 7) High levels of fatty acids. Fatty acids (from wort trub) inhibit bubble formation and head stability. 8) High alcohol levels. High levels of ethanol and/or fusel alcohols reduce surface tension. This is why strong beers don’t form as much head as weaker ones. 9) Age. Age reduces carbon dioxide levels and breaks down compounds which help form and retain head. 10) Large bubbles. Smaller bubbles produce greater head. Nitrogen served beer works on this principle. 11) Excessive agitation. Shaking up beer can make it “use up” foam-producing compounds. To Improve Head Formation and Retention: 1) Clean. Properly clean brewery equipment & serving containers. Oils and fats kill head retention, as do dish and dishwashing soap. Use different cleaners and rinse thoroughly. Use proper beer glassware cleaning agent for your beer glasses. 2) Alter Grist. Use body & head enhancing malts with high dextrin & protein levels., e.g., Crystal, Carafoam™, wheat, oats. Reduce percentage of fermentable adjunct sugars. Drawbacks: Can interact with tannins to promote chill haze, suspended starch/protein particles reduce clarity. Risk of stuck mash when using malts with high levels of proteins or gums. 3) Alter mash schedule to enhance head-retaining proteins. A) Avoid Beta-Glucan rest (110 °F) unless dealing with v. gummy mash (e.g., rye, oats). B) Use a protein rest (122 - 140 °F for 20 minutes). Use a protein rest to increase polypeptide levels, especially when using undermodified malts. This promotes the formation of short and medium-chain proteins, thus promoting head forming compounds. C) Avoid a long protein rest (1+ hour): This can break down proteins too much, which will negatively affect head formation. D) High Temperature Mash. Mashing at 154-162 °F at 5.5 - 5.6 pH promotes Dextrin formation by favoring Alpha-Amylase action. E) Reduce wort gravity to reduce alcohol levels. Drawback: Less booze in your beer, not appropriate for all styles. 4) More high alpha acid bittering hops. Increasing isohumulones increases head formation. Drawback: Increased hop bitterness. 5) Vigorous wort boil. Breaks down proteins into short and medium-length polypeptides. 6) Proper separation of cold break. Trub formed during cold break consists largely of fatty acids, which can impair head retention. 7) Pitch healthy yeast in sufficient amounts. Damaged or insufficient yeast can produce higher levels of a mino acids, which can damage foam. Pitch at least 1 million cells x 1 °P x 1 ml wort (usually 1-1.2 gal. yeast starter/5 gallons of wort, more for lagers). Properly aerate wort immediately after pitching to avoid formation of fusel oils. Avoid fusel oils/h igher alcohols by fermenting at lower temperatures for yeast strain. 8) Proper sanitation. Bacteria & wild yeast can metabolize dextrins & proteins, destroying compounds which aid head formation as well as increasing alcohol levels. 9) Don’t filter excessively. Extremely fine filters can remove suspended yeast/starch particles, as well as dextrins and polypeptides, all of which aid foam formation and stability. 10) Don’t use amylase or protease enzymes. Enzymes such as amylase and papain added to green beer indiscriminately attack dextrins and proteins, causing thinner body and poorer head retention. 11) Avoid oily additions to beer (e.g., meat, nuts, some fruits, spices, herbs & vegetables). 12) Proper packaging and serving. Get the proper carbonation level for the beer style. Don’t agitate kegs to get CO2 into solution., it breaks down foaming and stabilizing compounds. Some styles of beer are dispensed using nitrogen gas and special taps (“sparklers”) to produce smaller bubbles. Use proper glassware ( smaller, properly-shaped glasses with etched nucleation points). Don’t eat oily food or wear lip balm or lipstick when tasting beer. 13) Heading Agents. Most added at bottling time. Common types are iron salts, gums (e.g., xantham, gum Arabic), alginates & medium molecular weight polypeptides, such as Pepsin - derived from pork. Drawbacks: All alter flavor & mouthfeel, making beer seem "softer." Usually not necessary for all-malt beers, used for commercial high-adjunct lagers. 14) Nitrogen ( N2) or Mixed ( CO2/N2) gas dispense. Produces finer, longer-lasting bubbles. Drawbacks: Removes CO2 "prickle" or "bite" altering mouthfeel. Difficult for homebrewers to set up. Requires special equipment. Not appropriate for many styles. 15) Don’t age beer. Head-forming proteins and gums can break down over time. When Is Low/High Head Formation and/or Retention Appropriate?: High head formation, usually with lingering persistence, is expected in any beer with a high level of alpha acids, proteins and/or starches, specifically: Dortmunder export, German pilsner, Bohemian pilsner, Vienna Lager, Oktoberfest, Munich dunkel, schwarzbier, bock (except eisbock), American wheat or rye, Düsseldorf altbier, strong Scotch ale, Baltic porter, stouts, IPA, German wheat and rye beers, French and Belgian ales (except for some Belgian specialty ales), Berlinerweisse, Gueuze and Belgian strong ales. Low head retention is appropriate for any thin-bodied and/or aged beer, specifically light American lager, standard American lager, premium American lager, dark American lager, eisbock, cream ale, Kölsch, Berlinerweisse and unblended lambic Some beers, especially aged and high alcohol beers, might have poor head retention, even if they have strong initial head formation: strong Scotch ale, Russian imperial stout, Berlinerweisse and strong ales. Cask-conditioned ales (e.g., English pale ales, mild, Scottish ales, Irish ale) might have low head formation and retention due to low carbonation levels rather than thin body.

Honey-like aromas and flavors are caused by specialty malts, yeast character, actual honey additions or oxidation. Chemicals which can produce honey-like notes include 2, 3-pentanedione, ethyl hexanoate, ethyl phenylethyl acetate and phenylacetic acid. See Esters, Malty, Oxidation, Sherry-Like, Sweet and VDK for more information.

Hops.

? mg/l.

Imparted by additions of flavor hops, aroma hops and/or distilled hop oils. See Hoppy.

Hops.

Variable, usually ~0.15 mg/l for dry hops, 0.01 - 0.2 mg/l for kettle hops.

Various essential oils found in hops impart distinctive hoppy aromas and flavors to beer. They are imparted to beer by adding hops during wort boiling, during wort cooling (e.g., by letting hops steep in cooling wort or by running hot wort through a hopback), or by dry-hopping finished beer. The most volatile chemicals (usually the smallest molecules) are quickly driven off during wort boil and only survive in aroma hop and dry hop additions. The larger, less volatile molecules last longer and are responsible for hop flavor (apart from hop bitterness, which is due to isomerized alpha acids). Of the essential oils, the two most important families are: A. Hydrocarbon-Based Oils: Monoterpenes & sequiterpenes. They represent about 75% of essential oils. Within this group, the most important sub-groups are: I. Monoterpenes. a) Humulene has a delicate, refined flavor and oxidizes to produce spicy notes. “Noble” hops have high humulene levels. b) Myrcene is more pungent, and is higher in U.S. hops. It oxidizes to produce citrusy or piney notes. II. Sequiterpenes: Farnesene & Caryphyllene. They oxidize to compounds with “grassy” aromas. B. Oxygen-Bearing Oils: Also called essential alcohols, they represent about 25% of essential hop oils. Within this group, the two most important molecules are: I. Linalool has a hoppy aroma. II. Geraniol has a floral, perfumy aroma like geraniums, roses or cheap perfume. In some cases it can smell like fresh grass. Typical Concentration in Beer: 0 - 100 µg/l (depending on hop level and strain used). Perception Threshold: A third of the population have a threshold of about 18 µg/l. The remainder have thresholds around 350 µg/l. Beer Flavor Wheel Number: 0162. C. Ketones: Ketones are similar to alcohols and aldehydes, but they have a double-bonded oxygen molecule in the middle of the molecule. Hop-derived ketones can have floral, herbal or spicy notes.

Microbial contamination.

~420 µg/l.

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. See Oxidation, Phenolic and Sour for more information. Since Brettanomyces are slow-growing yeasts, Brett infection rarely appears by accident, and usually only shows up in aged beers. Brett infections are more likely in beer with higher pH, where oxygen is present in the beer and the beer temperature is warm (68 °F or above). Typically, Brett produces 4-EP to 4-EG at about an 8:1 ratio, but since humans are more sensitive to 4-EG, the flavors balance out.

Malt.

? mg/l.

See Astringent and Grainy.

Yeast, infection.

? mg/l.

See Sulfidic.

Improper packaging.

n/a.

When judging homebrew, judges should never deduct points for an unusually high or low fill level, nor should they assume that a high or low fill level is a sign that the beer is flawed. In properly-filled 12 oz. bottle (i.e., filled with about 12 oz. of fluid) the fill level just reaches the bottle’s neck, leaving 1-3” of empty space between the beer and the bottle cap. Likewise, larger bottles are designed so that when the bottle is properly filled the contents just reach the neck of the bottle. Legally commercial beer must be packaged so that the consumer gets at least the volume of beer stated on the label. But, for reasons of cost, brewers d on’t want to give away free product by overfilling their bottles. So, the ideal fill level is one which is right at, or just above listed volume. To hide the fact that the neck of the bottle is empty, most beers have labels around the neck. Historically, the need for the space between the fill level and the cap was to keep the beer from touching the bottle cap, since the cap could rust and impart metallic off - flavors to the beer. Fill levels for bottles of homebrew are much higher, sometimes 14 oz. or more in a 12 oz. bottle. This is because homebrewers want to fill as few bottles as necessary to bottle their beer and because the filled bottle “looks right” if the fill level is at least halfway up the bottle’s neck. Homebrewers who force carbonate their beer and bottle using counterpressure bottle fillers often “cap on foam” by filling the bottle right up to the lip. This helps to reduce oxidation by to eliminating headspace. Brewers who bottle condition their beers typically leave a bit more headspace. While on its own a high or low bottle fill is harmless, it might be the origin of actual faults. An unusually low fill level (i.e., below the shoulder of the bottle) might result in problems with oxidation or low carbonation levels. An unusually high fill level might result in low carbonation levels, yeast-derived fermentation faults (if the beer was improperly bottle conditioned) or metallic off-flavors due to contact with the bottle cap.

Contamination.

5-15 µg/l. About half the population is very sensitive to indole while the remainder is not.

Contamination.

? mg/l.

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. Also see Bromophenols, Chlorophenols, Phenol, Smoky, Spicy and Vanilla.

Yeast.

? mg/l.

See Esters.

Hops, aging, process faults.

0.7-1 mg/l. While everyone can taste isovaleric acid, perception threshold levels can vary by several orders of magnitude.

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.

? mg/l.

See Esters and Sweet.

Hops.

? mg/l.

See Bitter and Hoppy.

Microbial contamination.

0.04 mg/l.

Caused by infection by various forms of Gram-positive bacteria, most commonly Lactobacillus, but also Pediococcus (although lactic sourness is only obvious after diacetyl has been reduced), both of which are present in dust and saliva. Acidulated malt can also introduce lactic sourness without the need for bacterial infection. Likewise, lactic acid, normally used to reduce mash pH can be used to sour beer. Lactic acid is mostly non-volatile so it is odorless except in high concentrations. It has a crisp, clean, tart sourness reminiscent of yogurt.

Aging.

10 µg/l.

An off-characteristic associated with the intermediate stages of aging in beer, often found in conjunction with Woody notes. Represented by the compound 6-Isobutylquinoline. Leathery compounds act synergistically with paper (q.v.) flavor to impart stale aroma and flavor. The precise origins of leathery stale notes are unknown. Also see Almond, Catty, Oxidation, Papery and Sherry-like. Fermentation by Brettanomyces strains can also impart leathery notes to beer. See Caprylic and Horsey.

Malt, oxidation.

? mg/l.

See Malty and Oxidation, except possibly aged beers such as Old Ales where they are acceptable at very low levels.

Mishandling.

4 ng/l.

Lightstruck character is caused by a photochemical reaction where visible or ultraviolet light (wavelengths below 520 nm) makes riboflavin in the beer react with and break down hop-derived, sulfur-containing isohumulones (isomerized alpha acids). This liberates 3 - methylbut-2-ene-1-thiol, a mercaptan, a compound detectable at just a few parts per billion, which is similar to the active ingredient in skunk musk. For this reason, mercaptans are added to natural gas (methane), which is naturally odorless, as a safety precaution. This leads some people to wrongly assume that household natural gas naturally smells like mercaptans. The wavelengths of light responsible for triggering the lightstruck reaction are found in both sunlight and ordinary fluorescent lightbulbs. They readily penetrate all but dark brown “amber” glass, causing the contents to become “skunky” in as little as 30-120 seconds. Amber glass bottles allow about 5% of ultraviolet light (below 400 nm) to pass, while green glass allows about 80%.Between 400-520 nm (violet to green light), amber glass lets 5-30% of light pass (depending on frequency), while green glass allows 50-80% to pass. Clear glass and glass allows about 90% of all wavelengths to pass. Some large commercial brewers avoid the problem of lightstruck beer in their signature products (e.g., Corona, Miller Highlife) by using a chemically modified form of isohulone which doesn’t react with riboflavins. This allows them to ship their beer in cheaper, more attractive green or clear bottles.

Malt.

Variable, depending on type and beer style. Some compounds can be detected in µg/l.

Drying, kilning and roasting malt produces a vast variety of aromas and flavors associated with Maillard reactions. Maillard reactions occur when reducing sugars react with amino acids at high temperatures, and moderately moist conditions, producing N-substituted glycosylamine and water. The unstable glycosylamine then undergoes Amadori rearrangement, forming ketosamines. These compounds react further, either forming water and reductones, nitrogenous polymers and melanoidins, or producing pyruvaldehyde and other short-chain hydrolytic fission products. Maillard reactions are different from caramelization which is the pyrollization of sugar under extremely high, dry heat. Products formed by Maillard reactions are still poorly understood, but commonly include heterocyclic compounds such as acrylamides, pyradines (e.g., 2-acetylpyridine, 6-Acetyl-2,3,4,5-tetrahydropyridine - which give biscuity, cracker-like notes) and melanoidins (which give roasted or toasted foods their characteristic brown or black colors). Other products include furans, pyrazines, pyrroles and thiopenes. Depending on the temperature and duration of drying, kilning and/or roasting malt might have flavors and aromas ranging from bready to burnt grain. In conjunction with sugars and dextrins in the beer, these compounds might also exhibit characteristics reminiscent of caramel, toffee, treacle, molasses and similar caramelized sugars - although the process of Maillard reactions is different from the process of caramelization. Beers that have been contaminated with caustic, or which are otherwise higher in pH than normal will have more pronounced pyridine and acrylamide notes.

Malt.

? mg/l.

See Grainy or Malty.

Yeast.

? mg/l.

See Autolyzed, Umami or Yeasty.

Yeast.

? mg/l.

See Esters.

Yeast, microbial contamination.

1 µg/l.

Caused by chemicals such ase thanethiol, 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. Alsos ee DMS, Hydrogen Sulfide and Lightstruck.

Contamination.

1-1.5 mg/l.

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. 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.

Infection.

? mg/l.

Caused by 3-Methylthiopropionaldehyde. See Sulfury or Vegetal.

Water.

Variable.

Mineral character can be imparted to beer by using brewing water which is high in certain non-metallic mineral salts, or by adding excess levels of brewing salts to beer. Sulfate aids isomeration of alpha acids, and increases perception of hop bitterness. In excessive levels it can produce a harsh, lingering hop bitterness. On its own, it can produce a detectable aroma. Chloride enhances perception of sweetness at low levels, but can seem bitter at higher levels. Calcium, carbonates and bicarbonates can see chalky or plaster-like at high levels. Magnesium can seem bitter at high levels. At low levels, sodium, rather than seeming salty, can seem slightly powdery or minerally.

Contamination.

? mg/l.

See Oily.

Malt, sugar adjuncts.

? mg/l.

See Malty and Sweet.

Infection, Contamination.

? mg/l.

See Musty.

Malt, grain adjuncts, yeast.

? mg/l.

See Body, Oily and Vicinal Diketones.

Contamination.

<10-25 ng/l.

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). Rarely, musty notes can arise due to overpasteurization of beer or contact with improperly cleaned packaging materials. In some cases, very low levels of Metallic character might be confused with Musty flavor.

Malt, oxidation.

? mg/l.

See Almond, Malty or Roasty.

Malt, adjuncts, contamination.

? mg/l.

See Body, Fat, Oil or Hydrocarbons, Silky or Vicinal Diketones.

Grain, contamination.

0.1 µg/l.

Onion, garlic or cooked onion notes in beer comes from mercaptans, such as Ethyl mercaptan and propyl mercaptan, as well as diethyl sulfide. These are produced from sulfur-bearing amino acids naturally found in malt during wort boiling. They are purged from beer during fermentation by yeast-derived CO2. To a lesser extent, they are derived from hop oils during wort boiling or aging. Bacterial contamination can also produce onion or garlic notes, but usually along with much more prominent “rotten vegetable” or “rotten egg” notes.

Malt, adjunct sugars.

See Sweet.

Aging, process faults.

Variable depending on exact chemical.

Oxidation is the interaction of dissolved oxygen with other chemical compounds in beer, usually formy carboxyl compounds. It is the major source of flavor instability during beer storage. Oxidation is increased by introducing air to wort or beer after fermentation has begun and by storing beer at high temperatures in non-airtight containers. There are many pathways which cause flavor instability in beer, some of which are discussed elsewhere; also see Almond, Catty, Leathery, Papery and Sherry-like. Flavor instability is noted as a progressive drop in hop bitterness (the remaining bitterness can become harsher), hop flavor, hop aroma, and Esters. Changes in flavor or aroma due to flavor instability are more perceptible in blander beers than more full-flavored ones. In early - to mid-stage oxidation, beer might develop “ribes” (blackcurrant leaf or tomcat urine) and/or Leathery notes which fade with time. As the beer ages, it might also develop honey, bready or toffee-like flavors and a sweet or honey-like aroma. With time, the beer might develop distinct Papery or “tomato juice” (see Papery), and/or Almond, Isovaleric or Sherry-like notes (q.q.v.). The latter can sometimes be perceived as vinous or woody. Likewise, harsh or solventy higher alcohols might degrade to more pleasant Esters or Aldehydes, and the beer might develop Earthy, Metallic, straw-like (see Grassy) notes. Beer aged at 77 °F (25 °C) tends to develop caramel notes while at 86-99 °F (30-37 °C) it develops more papery notes. Changes in flavor or aroma due to flavor instability are more perceptible in blander beers than more full-flavored ones. The main factors in oxidation are levels of dissolved oxygen in the beer and temperature. Oxygen can be introduced into the beer at any stage during the brewing process, from mashing to conditioning. Except when aerating the wort to improve yeast performance (the yeast takes up the dissolved oxygen within a few hours), brewers should take every step possible to avoid aerating their brewing liquor, mash, wort or beer. Commercial breweries take great pains to prevent oxygenation at all phases of production. During mashing, mash is “doughed in” in an oxygen free environment and, ideally, mash is pumped into the mash tun from below to minimize oxidation of the mash. Sparge liquor is deoxygenated and is pumped into the lauter tun under oxygen free conditions. Pumps and other equipment are checked to make sure that oxygen doesn’t get into the mash or wort during transfer. Wort boil, fermentation and conditioning also takes place in oxygen free environments. Modern packaging equipment means that modern commercial bottled beer has less than 0.1 ppm dissolved oxygen. Aeration of the sparge liquor during recirculation (AKA “hot side aeration”) is a major factor in oxidation of homebrewed beer. Splashing or aerating mash liquor, sparge liquor, wort or beer during transfer or packaging are other sources of oxidation in homebrew. Regardless of oxygen levels, rate of flavor change depends on temperature. Beer stored at 32-39 °F (0-4 °C) shows no oxidation even after many months of storage, while beer packaged under low oxygen conditions might show signs of aging after about 100 days at 68 °F (20 °C). Storage at higher temperatures results in a 2-3 fold increase in aging rate; beer might show signs of oxidation at 30 days if held at 86 °F (30 °C), while beer held at 140 °F (60 °C) will show signs of oxidation after just 1 day! Pathways involved in synthesis of staling substances include: - Melanoidin-Catalyzed Oxidation of Higher Alcohols: Alcohols in beer can be converted to their equivalent aldehydes through the catalysis of melanoidins. - Oxidation of Iso-alpha-acids: Might be involved in staling of beer. Hop fractions less prone to staling. - Strecker Degradation of Amino Acids: Reactions between amino acid and an alpha-dicarbonyl compound, such as the intermediates in browning reactions. The amino acid is converted into an aldehyde. Polyphenols may have a catalytic role. - Aldol Condensations: Reactions between separate aldehydes or ketones is route through which (E) -2-nonenol might be produced by an reaction between an acetaldehyde and heptanal. Diverse other carbonyls might be generated in this way, with the amino acid proline as a catalyst. - Oxygenation of Unsaturated Fatty Acids: Oxidative breakdown of lipids can cause sulfury or rancid notes in beer. Antioxidants naturally found in beer, which block oxidation, include: - Polyphenols: These compounds scavenge oxygen free radicals, superoxide and hydroxyl, inhibit lipoxygenase and act as chelating agents - sequestering metal ions such as iron and copper. Unfortunately, they also cause astringency and chill haze. - Melanoidins: The compounds scavenge superoxide, peroxide & hydroxyl, but also promote formation of higher alcohols. - Sulfur dioxide: SO2 scavenges free radicals, but carbonyls bind with SO 2 in brewing process and SO2 are lost in beer through unknown means (half is lost in 27 days at 104 °F - 40 °C -, 3 years at 32 °F - 0 °C ). As SO2 is lost carbonyl compounds are freed, resulting in flavor instability. - Yeast: Yeast produces SO2 and reduces carbonyl compounds to fusel alcohols. - Chelation: Various chemicals in beer, such as amino acids, phytic acid and melanoidins, chelate metallic ions, preventing them from accelerating flavor instability. - Sulfites (e.g., Potassium metabisulfite) added to beer immediately reduces carbonyl compounds, eliminating many “stale” characteristics. The problem is that sulfites contribute unwelcome sulfury notes to beer and are toxic to yeast, making it impossible to use them in cask or bottle-conditioned beer. In some cases, their use is also restricted or prohibited by law, making commercial brewers hesitant to use them.

Aging, process faults.

50 - 100 ng/l.

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 “librar y” (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.

Infection.

? mg/l.

See DMS, Sulfury or Vegetal.

Yeast.

? mg/l.

See Esters. Peaty Peat-smoked notes in beer are usually due to the use of peated distiller’s malt, but low levels of peat character might be imparted to beer by certain yeast strains or use of water contaminated with bacteria, mold or decaying plant material. See Earthy, Phenols and Smoky.

Yeast.

? mg/l.

See Esters and Solventy Esters.

Yeast, microbial contamination, process faults.

Variable depending on exact chemical; usually about 0.2 mg/l.

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 non - volatile 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. Common phenols found in beer are given below, along with their specific sensory characteristics and biochemical origins. Also see Bromophenol, Chlorophenol, Iodoform, Smoky, Spicy and Vanilla. - Flavanoids (AKA Bioflavanoids, Flavanols): This is a huge family of phenols with ket one-containing compounds which are naturally found in many plants. They have often little aroma, although they can be precursors to aroma compounds. 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. Flavanoids are present in grain husks, and the process of roasting or toasting malt oxidizes or pyrolyzes these compounds during Maillard reactions to produce the distinct flavors of biscuits, bread crusts, burnt grain bitterness, chocolate coffee, roasted grain or toast. Flavanols are also present in many fruits, especially cherries, citrus and grapes. - 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. Polyphenols in beer are mainly extracted from grain husks due to improper grain milling, mashing or sparging technique, but they can also be extracted from water left to stand in contact with decaying plant material, or from hops. Herbs, spices and fruits can also impart polyphenols. Beer aged in contact with wood will also pick distinct oaky or woody notes from polyphenols. With time, these compounds will react withal cohol to produce vanillin, imparting the flavor and aroma of Vanilla (q.v.). Beer left on the yeast cake for excessive amounts of time might also pick up polyphenols liberated during yeast autolysis. Polyphenols can bind with suspended proteins in beer to form protein/chill haze. They can also form oxidized fusel alcohols due to a reaction with aldehydes, if oxidized by hot-side aeration or poor storage conditions. Over-attenuation and low dextrin levels (i.e., thin-body) can increase the perception of astringency.

Hops, herb additions.

variable.

Piney notes are typically caused by Esters and Phenol (q.v.) compounds found in hops, especially modern American varieties. Specific aroma and flavor compounds are hydrocarbon-based essential oils, which naturally occur in hops, such as a-humulene, a-Muurolene, b-caryophyllene, b-pentene, b-Selenene, mitral, D-matinee Farnesene, Farnese, Geraniol, l-matinee, limonene, limonene-10-ol, myrcene Nerol, terminal. Not surprisingly, these compounds are also found in pine trees and other conifers. Some specialty beers, notably holiday beers, spruce beers, and historical Scandinavian beers such as Finnish Sati and Swedish Gottlandstrikka, might have pine or spruce additions. The wort used to produce historical Scandinavian beers is traditionally filtered through a bed of young pine needles. Pine - flavored holiday beers typically use spruce or pine flavoring. These flavorings are very intense and can easily be overdone. Note that traditional spruce beer, made with new spruce tips, doesn’t produce piney notes. Instead, the flavor and aroma is much more herbal and citrusy. Older spruce tips can impart bitter and pine-like characteristics.

Microbial contamination, contamination.

20 µg/l.

Plastic notes are generally due to common plastics (e.g., styrene), lacquers (e.g., epoxy resin), or plasticizers (e.g., phthalates) introduced to beer due to contamination of brewing equipment or packaging materials. Phenolic notes reminiscent of plastics can also arise in beer due to wild yeast infections. Rarely, plastic notes can also arise in beer due to contaminated CO2.

Malt, hops, yeast, contamination.

? mg/l.

See Mouthfeel or Sediment.

Sugar adjuncts.

See Sweet.

Malt, yeast, oxidation.

Raisin-like aroma and flavor is due to Esters (q.v.) which arise due to the use of certain strains of yeast or the use of certain brands of crystal malt, notably DeWolf-Cosyns Special-B™. Raisin-like character can also develop due to age and oxidation, see Sherry.

Oxidation, contamination.

See Oily or Oxidation.

Oxidation, contamination.

See Oily or Oxidation.

Yeast.

? mg/l.

See Hoppy, Pine or Spruce.

Dry hopping, yeast, added ingredients, contamination.

When judging homebrew, judges should never deduct points just because a beer has a ring around the neck, nor should they assume that the presence of a ring is an indication that the beer is flawed. Some homebrewed beer might have a whitish or brownish “ring around the collar” just at the bottle fill line. This is a purely cosmetic fault. A brownish or greenish ring of material is probably due to residual hop material or hop resins and oils. This is likely the case if the beer was dry hopped before being bottled. Other plant material, such as herbs or spices, can also leave a brownish or greenish ring. A whitish ring is either due to yeast activity or due to the use of dry malt extract, especially if the beer is bottle-conditioned and was primed using dry malt extract. In some cases, though, it might be a sign of a bacterial or wild yeast infection, or added starchy or oily ingredients (e.g., coconut). A clear, slimy ring might be due to added ingredients, but it could also be a sign of a wild yeast or bacterial infection. See Film on Top of Beer for more information.

Malt.0422

See Malty.

Malt.

Variable, depending on type and beer style. Some compounds can be detected in µg/l.

The flavors and aromas of darker malts are actually a sub-class of Malty (q.v.) characteristics found in combination with various phenolic compounds (notably flavanoids and monophenols), which are produced when malt is kilned at high temperatures. Maillard reactions, which occur at higher kiln temperatures, produce a variety of compounds which give flavors ranging from biscuity or nutty to coff ee-like or burnt. From lighter to darker malts, typical toasted or roasted flavor compounds are as follows: Lightly Toasted Malts: Light to medium amber in color, producing flavors and aromas reminiscent of biscuits, crackers or Graham crackers. Toasted Malts: Dark amber to light brown, producing characteristics reminiscent of bread crust, nutty or toasted. Roasted Malts: Medium to dark brown, producing characteristics reminiscent of chocolate, coffee or espresso. Black Malts: Dark brown to black, with a burnt or bitter flavor and aroma. In conjunction with sugars and dextrins in the beer, these compounds might also exhibit characteristics reminiscent of caramel, toffee, treacle, molasses and similar caramelized sugars - although the process of Maillard reactions is different from the process of caramelization. See Malty and Phenols for more detailed discussions.

See DMS or Vegetal.

Water, process faults.

200 - 500 mg/l.

The ability to detect saltiness is one of the basic tastes in humans. 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. At sub-threshold, sodium enhances the perception of sweetness in beer. Saltiness is detectable at 100-1,000 mg/l in water, although most people detect it at 100-500 mg/l. IN beer, it can be detected at 200 mg/l. To Reduce or Avoid: Limit brewing salt additions, particularly sodium chloride. Don’t use water treated by ion - substitution water softening systems. Commercial brewers who use brine as a refrigerant might get salty notes in their beer as a result of a refrigerant leak.

Malt, adjunct sugars.

See Body

Dry hopping, yeast, added ingredients, contamination.

When judging homebrew, judges should never deduct points just because a beer has sediment at the bottom of the bottle, nor should they assume that the presence of sediment is an indication that the beer is flawed. They should also refrain from deducting points from appearance if the beer was clear in the bottle, but was subsequently roused due to rough handling. Likewise, high levels of sediment can alter perceptions of aroma, appearance, flavor and mouthfeel. Judges should learn to pour carefully to avoid rousing sediment and should avoid sampling beer from the bottom of the bottle. This is especially important when only one bottle of beer has been entered in competition, and it must go on to a mini-Best of Show or Best of Show round. Some homebrewed beer might have sediment at the bottom of the bottle. By itself, this is a purely cosmetic fault, as long as the layer of sediment is sufficiently thin that it is possible to carefully pour the contents of the bottle without rousing the sediment. Sediment might contribute to other faults in beer, however, such as off-flavors and aromas caused by autolyzed yeast. Grayish tan sediment is usually due to yeast. Sediment of other colors is due to settling of fine particles of other materials, such as malt, hops, herbs or spices. Otherwise clear beer, which has been aged for a long period of time, might have a layer of sediment on the bottom of the bottle. As a rule of thumb, the more tightly compacted the sediment, the older the beer. In commercial beer, this is usually a sign that the beer is very old, and might have characteristics associated with extended aging. For homebrew, the presence of sediment isn’t as good an indicator of age. If a beer which should be cloudy is clear or hazy, but has a thick layer of sediment at the bottom, it is usually a sign that the beer has aged for a while. While this isn’t a fault in itself, since the sediment can be roused back into suspension, but it might be a warning that the beer has deteriorated due to age. For styles of beer where cloudiness is expected, such as witbier and unfiltered German wheat and rye beers, the presence of sediment can be a fault if the roused sediment has a gritty or sandy texture. This is usually a sign that trub from theb ottom of the fermentation vessel was added to the beer. Cheap commercial hefeweizens are sometimes produced in this fashion.

Aging.

?.

Sherry notes emerge when melanoidins, alcohol and oxygen interact, reducing volatile molecules such as esters and hop compounds. They only form in strong (6+% ABV) dark-colored (20+ SRM) beers and often accompany a darkening of the beer. These compounds sometimes develop from compounds which are responsible for less pleasant flavors earlier in the oxidation process (e.g., inky, musty, rotten fruit) and are reminiscent of aged red wine, dark fruit (e.g., dates, figs, prunes, plums, raisins), dry sherry, honey, nuts (e.g., almonds, hazelnuts, walnuts) and/or port wine. These compounds might be reduced back into their original form by oxidizing alcohols into aldehydes. Also see Almond, Leathery, Oxidation and Papery.

Infection.

? mg/l.

See DMS.

Malt, carbon dioxide or nitrogen gas.

n/a.

Silkiness in beer can come from three sources, either high levels of proteins from grains such as wheat or oats, Oiliness from grains such as oats or dispensing the beer using nitrogen gas and special taps. Protein-derived silkiness or creaminess in mouthfeel is caused by low to medium-weight peptides and polypeptides, which also improve Head Formation and Retention as well as perception of body. Low levels of oils in beer can also increase the perception of silkiness. Typically, these are imparted to beer at very low levels by the use of malts or adjunct grains which have higher residual levels of oils. Odd adjunct ingredients in specialty beers, such as nuts or peanuts, might also impart natural oils. Also see Fat, Oil or Hydrocarbon. Some varieties of beer (notably dry stouts, but virtually any variety of English, Scottish or Irish ale ) are dispensed using nitrogen gas or a mixture of carbon dioxide and nitrogen (“beer gas”). The beer is further exposed to nitrogen gas by being passed through a special “sparkler” tap which aerates the beer as it is poured, making it foam. When some or all of the carbon dioxide in the beer is replaced with nitrogen, the beer produces smaller, more densely packed bubbles. This gives the beer a thicker, rockier, more finely-beaded head with improved retention and a creamy texture. In addition to the creamy texture character carrying through into the overall mouthfeel, the lack of carbon dioxide “bite” and “sharpness” make the beer seem sweeter and maltier. Some commercial canned beers incorporate a “widget” which is partially or completely filled with nitrogen gas. When the can is opened, the gas in the widget is released as the surrounding carbon dioxide pressure is reduced; giving the beer the characteristic nitrogen dispensed creamy head and mouthfeel. Also see Body, Head Formation and Retention and Vicinal Diketones.

Malt, process faults, contamination.

15 µg/l.

Smoky notes arise due to monophenols; simple phenols with a hydrocarbon side chain. In brewing they occur as minor compounds during pyrolysis (heating material in the absence of oxygen), such as scorching wort/mash or smoking

? mg/l.

Yeast.

8-42 mg/l.

Solventy esters occur when alcohols are reduced by oxygen. As such, they naturally occur in all beers. The most common solventy ester is ethyl acetate, which occurs when ethanol undergoes esterification. As with other esters (see Esters) ester production is increased when fermentation is vigorous (e.g., higher temperature fermentation) or when the yeast is stressed (e.g., insufficient yeast cell count or oxygen levels). Some strains of wild yeast can also produce high levels of solventy esters. Also see Esters, Fusel Alcohol, and Oxidation.

Aging.

~6 ng/l.

Solventy-stale notes are due to furfural ethyl ether (FEE). Its precursor, furfural alcohol, is produced by Maillard reactions (see Malty) during malt kilning and during wort boiling. Over time, ethanol interacts with furfural alcohol to form FEE. Beer stored at room temperature can develop perceptible levels of FEE after just 1 month. Beer stored at room temperature for 6 months can have concentrations of FEE up to 200 ng/l. Beer held at high temperatures (100 °F) can develop detectable FEE levels in just days. Furfural alcohol and FEE are found in higher concentrations in dark beers, especially dark ales. Lower pH, darker color and higher alcohol content enhance FEE formation, while sulfite inhibits it. Note that oxidation doesn’t play a role in FEE production, so the usual steps to avoid oxygenation don’t apply. Also see Leathery, Oxidation, Papery and Solventy/Solventy Esters.

Adjunct spices or sugars.

? mg/l.

Sotolone is the chemical responsible for the aroma and flavor of maple syrup and fenugreek, as well as some of the aromas found in curry powder. See Phenols.

Yeast, malt, Microbial contamination.

170 mg/l.

The ability to detect sourness is one of the basic tastes in humans, and most food and drink is acidic to some degree. Beer typically has pH 4.0-4.5; below this, sourness can become noticeable and possibly unpleasant. Beer pH indirectly influences the flavor activity of a number of other chemicals and can affect perception of flavors and aromas. Sourness in beer is due to excessively low pH due to high levels of organic acids in the beer. Acidic compounds are perceptible at 300 mg/l or lower. Any sourness in beer is due to added acids (e.g., fruit or food-grade acids) or bacterial action. The two most important acids found in beer are Acetic acid and Lactic acid. They are described in their own sections. Other forms of sourness in beer include: - Ascorbic Acid: Mistakenly thought to be an anti-oxidant for beer, it is sometimes added at bottling. It can complex with yeast to produce ethyl acetate ( see Solventy). It has a crisp, citrusy sourness. - Citric Acid: Used to lower mash pH and also naturally present in citrus fruits. It can appear in beers made with extremely high levels of adjunct sugars or in fruit beers. It has a tart, lingering, citrusy sourness. - Naturally-Occurring Acids: Yeasts naturally produce organic acids such as oxalic acid, pyruvic acid and succinic acid, which have the effect of lowering beer pH as compared to the pH of the unfermented wort. They have a crisp, tart sourness and are not particularly volatile, making them hard to detect in aroma. Fatty acids are carboxylic acids with an alip hilic (i.e., hydrocarbon) tail. They are essential for yeast nutrition while the wort is fermenting, but can contribute to flavor instability in finished beer. They tend to produce unpleasant and aromas flavors when oxidized - see Butyric, Caprylic, Isovaleric and Horsey. - Malic Acid: Used in wine and cider-making, it is naturally present in many fruits, especially apples. It can appear in beers made with extremely high levels of adjunct sugars or in fruit beers. It has a cidery, tart, fruit-like sourness. - Phosphoric Acid: Used to lower mash pH and to wash yeast. Imparts a lingering sourness. - Roast Acidity: Present in dark malts due to kilning at high temperatures. Roast acidity is typically used to adjust mash pH when brewing dark beers. Adjusting mash pH downwards by 0.2-0.4 pH, depending on amount of dark malt used and the buffering capacity of the water. Roast acidity can impart a subtle, dry sourness to dark beers. - Sulfuric Acid: Commercial breweries sometimes use mineral acids to adjust mash pH or to treat water because of their low cost. Very rarely, homebrewers might contaminate their beer with mineral acid. Mineral acids have a sharp, pungent aroma and a harsh sour flavor. In high concentrations, they are both caustic and toxic. - Tartaric Acid: Used in wine making. Imparts a lingering sourness. Some Acids Found in Beer Acid Description Detectable range 3-Methylbutyric Sweaty 1.5 Acetic Vinegar 30-2175 mg/l Butyric Buttery, cheesy 0.5-2.2 Caproic Vegetable oil 8 Caprylic Goaty 15 Hexanoic Vegetable oil 1.0-5.0 Hexenoic Dry leaves 0.01 Oxalic 2-20 Phenylacetic Honey 2.5 Propionic Milky, acidic 1-150 Succinic 16-140 Valeric Sweaty 0.03-0.1

Yeast, microbial contamination, aging.

40 µg/l.

Spicy notes in beer are generally due to complex aromatic alcohols, a class of phenols with a multi - carbon and/or ester side chain. They are produced as minor metabolic products during yeast fermentation by the decarboxylation of phenolic acids via enzymes, especially by “Phenolic Off-Flavor Producing” (POF+) strains (e.g., Belgian and Hefew eizen strains, wild yeasts), and to a lesser extent by Acetobacter bacteria. They are also found naturally in herbs and spices. Phenolic compounds produced by brewers ’ yeast usually include clove-like, spicy or peppery notes. Wild yeasts or bacteria can produce bitter, medicinal, plastic, roasted or smoky notes in addition to more pleasant spicy notes. Oxidation might also produce phenolic bitterness, especially in the form of eugenol (clove-like) spiciness. Unlike other phenolic compounds, many complex aromatic alcohols are volatile, or easily degraded during storage, and will decrease as the beer is aged. Common complex aromatic alcohols as listed below. Also see Bromophenol, Chlorophenol, Phenol, Smoky and Vanilla. - 4-Vinyl Guaiacol: The most commonly produced phenolic compound, formed by phenolic off-flavor producing strains of brewers ’ yeast, especially German hefeweizen yeasts. It is formed during fermentation from its precursor, ferulic acid. It has a clove-like flavor and aroma. It is detectable at 40 ppb in water, 20 - 100 ppb in beer. - Capsicum: Found naturally in chili peppers. Responsible for chili-pepper “heat” due to capsicum acting on the trigeminal nerve. Capsicum strength is rated in Scoville Heat Units” (SHU), ranging from 0 (bell peppers) to 16 million (pure capsicum). By comparison, pepper spray has about 5 million SHU and Tabasco sauce has 500-8,000 SHU. - Eugenol: Found naturally in cloves (it ’s the active ingredient in clove oil), but also basil, bay, cinnamon and nutmeg. It can sometimes occur as an oxidation product as beer ages, especially in strong beers (ABV >7%). To Control: Causes: Yeast strain (e.g., Belgian or hefeweizen yeast). Yeast mutation. Wild yeast infection, usually by Saccharomyces Diastaticus (medicinal, plastic, smoky notes). Underpitching. High temperature fermentation (above ~68 °F). Aging - oxygenation of beer might produce eugenol. - To increase 4-vinyl Guaiacol: Use a ferulic acid rest during mashing (15 min. at 110 °F, at pH < 5.7). This liberates ferulic acid, the precursor to 4-vinyl guaiacol, which slightly aids in the production of clove flavor. Don’t repitch hefeweizen yeast (4-vinyl guaiacol production is highest in the first generation). Underpitch hefeweizen yeast. Ferment German wheat and rye beers at 62 °F. - To Reduce or Avoid: - Proper yeast management. Proper yeast strain. Avoid high-temperature (i.e., above ~68 °F) fermentation. Good sanitation procedures to avoid wild yeast infection. Don’t repitch yeasts for more than 5-10 generations from the original culture to avoid yeast mutation. Don’t reculture weak, old or mutated yeast. - Reduce or eliminate herb or spice additions. - Age beer properly - see Oxidation for details.

Oxidation

See Nutty, Oxidation, Papery and Solventy Stale.

Spice additions.

The primary aroma compound in star anise is 1-p-Methoxyphenyl-2-propanone. See Spicy.

Hops.

See Grassy.

Yeast.

? mg/l.

See Esters.

Yeast, microbial contamination, aging.

4-5 µg/l.

Hydrogen sulfide (H2S) is mostly produced by yeast during fermentation, and sometimes during maturation, by mechanisms which are still poorly understood. Yeast strain plays a major role; lager yeasts produce much more H2S than ale yeasts. There is more than one pathway involved. It might be formed due to breakdown of amino acids such as cysteine, or peptides such as glutathione, or by the reduction of inorganic sulfur compounds such as sulfate and sulfite. A small amount of H2S is formed during wort boil from sulfur compounds found naturally in malt. More H2S is produced in the presence of copper ions. During fermentation, most of the H2S is scrubbed out of solution by carbon dioxide, but some might remain in the finished beer. Low concentrations give beer a desirable “fresh beer” character, but high concentrations of H 2S are a defect. Bacterial infections (by Zymomonas, Pectinatus or Megasphaera species), can also produce large amounts of hydrogen sulfide, often in conjunction with other “off” flavors. H2S can also be released by dead yeast during autolysis, often in conjunction with other “off” characteristics. Finally, sulfite preservatives in cask finings might also release H2S. Extensive contact between beer and aluminum can also cause reactions which lease hydrogen sulfide.

Yeast, process faults.

7-20 mg/l.

Normally, yeast produces small levels (10 mg/l or less) of sulfur dioxide (SO 2) during fermentation. Higher levels are associated with added sulfites (e.g., potassium metabisulfite) used as anti-microbial, anti-oxidant and preservative. Sulfites block staling in beer by interacting with acetaldehydes and carbonyl compounds, temporarily masking their distinctive flavors and aromas. As beer ages, however, sulfites form sulfur dioxide, adding distinctive “off” - characteristics to the beer along with the usual staling compounds. High levels of sulfites (>10 mg/l) are toxic to yeast and bacteria. Levels of more than ~200-250 mg/l are toxic to people, but, fortunately, at that level, sulfite character is so strong as to be unpalatable. People with asthma are sometimes hypersensitive to sulfites, so U.S. and European law requires alcoholic beverages with more than 10 ppm of sulfites to be labeled with the warning: “Contains Sulfites.” Note: When spiking beer samples with sulfite, make sure than none of your tasters are sensitive to sulfites and that they have no history of asthma.

Yeast, microbial contamination, aging.

Variable.

These are various sulfury or sulfitic compounds which originate from sulfur-bearing amino acids (e.g., cysteine and methionine). Possible origins include malt type (especially pilsner malt), yeast strain, yeast autolysis, bacterial spoilage, water contamination, or high levels of sulfate ions in water treated with gypsum (calcium sulfate) or Epsom salts (magnesium sulfate). They can also arise due to overuse of sulfur-based antioxidants or antibacterial agents, such as potassium metabisulfite. While rare in beer, these flavors are common in over-sulfited ciders, meads and wines. Also see DMS, Sulfidic and Sulfitic.

Malt, adjuncts.

?.

Sweetness is one of the basic human senses. Sweetness in beer is caused by the presence of “reducing” sugars such as simple sugars (e.g., monosaccharides) and short chain polysaccharides (e.g., dextrins). Since simple sugars such as glucose, sucrose, fructose, maltose and maltriose are fermented by yeast, non-fermentable sugars, such as lactose, are sometimes used to impart sweetness in brewing. Alternately, the brewer might mash at the high end of starch conversion temperatures (~153-158 °F) to promote dextrin formation in the mash. Sweet beer might be pasteurized or filtered to remove the yeast and then force carbonated at packaging. The Plato scale corresponds to grams of sucrose per 100 milligrams of water. Degrees Plato (°P) roughly corresponds to S.G. at (1-S.G.)/4. In a finished beer attenuated to 1.008 to 1.010, this works out to 20-30 mg/l. Unintentional sweetness and poor attenuation in beer is likely due to poor yeast health which resulted in a slow or stuck fermentation. Common causes of slow/stuck fermentation are low FAN levels, low levels of dissolved oxygen in the wort, high gravity worts or high levels of alcohol. Premature flocculation due to shocks to the yeast (e.g., sudden temperature swings) might also result in underattenuation.

Malt, sugar adjuncts.

? mg/l.

See Sweet.

Equipment faults, contamination.

? mg/l.

This off-characteristic can a rise due to improper use of pitch to waterproof brewing equipment and beer storage containers. Given the ubiquitous use of stainless steel or food-grade plastic brewing equipment, this is a very rare problem, although it was once a problem when some beer barrels were lined with brewers pitch. If improperly heated, it can apparently impart resinous or turpentine-like notes to the beer. Also see Pine or Solventy.

? mg/l.

See Body.

Yeast, adjuncts.

?.

Umami represents the taste of the amino acid L-glutamate and 5’ -ribonucleotides such as guanosine monophosphate (GMP) and inosine monophosphate (IMP). Unlike other basic tastes, it was only identified recently (the flavor receptors for it were only identified in 2000) and its effects on flavor are subtle. Generally, rather than adding any flavor on its own, it balances tastes and rounds out flavors. Umami is found in aged meats, oily fish, milk, aged cheese (e.g., parmesan), fermented soy products (e.g., soy sauce) and vegetables such as tomatoes and seaweed.

Malt, aging, adjuncts, microbial contamination.

40 µg/l.

Vanillin, the active ingredient in vanilla, is formed by the breakdown of lignins, naturally found in plant cell walls, when exposed to alcohol and oxygen. It is formed in some beers, particularly those high in phenols (e.g., tannins) during aging. Vanilla is also produced during fermentation by strains of yeast ((POF+ strains) which produce phenolic off-flavors, from its precursor, ferulic acid. In such cases, it is usually accompanied by a similar molecule 4-vinyl guaiacol (see Spicy). In a few cases, vanilla notes might occur as part of a wild yeast infection. Some wild yeasts produce phenolic flavor compounds which are degraded to form vanillin.

Contamination.

? mg/l.

See Oily or Rancid Oil.

Yeast, microbial contamination.

10-40 µg/l. The ability to detect diacetyl is higher in light-flavored, low-alcohol beers, lower in more full-flavored beers. The ability to sense diacetyl is also genetic. Some people are sensitive to it down to 10 µg/l, others are insensitive to it. The typical threshold is 20-40 µg/l.

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. Bacterial infections, notably Pediococcus and Lactobacillus, can produce VDK in high concentrations, usually in conjunction with numerous other off-flavors and aromas as well. This is a common problem in infected (dirty) draught beer lines. - Diacetyl: Produced during fermentation as a byproduct of valine synthesis when yeast produces α-acetolactate, which escapes the cell and is spontaneously decarboxylated into diacetyl. The yeast then absorbs the diacetyl, and reduces the ketone groups to form acetoin and then 2,3-butanediol. Healthy yeast has about 10 times the ability to absorb diacetyl as to produce it. Diacetyl is typically detectable at 0.5 to 0.15 mg/l, although the ability to taste diacetyl is genetic. Some people can taste diacetyl down to 0.2 mg/l, while others are insensitive to it! It is described as tasting like artificial butter, butter, butterscotch, toffee or vanilla. - Pentanedione: 2, 3-pentanedione is produced during fermentation as a byproduct of isoleucine synthesis when yeast produces α-ketobutyrate, which escapes the cell and is spontaneously decarboxylated into 2, 3-pentanedione. The yeast then absorbs the 2, 3-pentanedione and reduces the ketone groups to form relatively flavorless compounds. Compared to diacetyl, pentanedione is much less important, since the perception threshold is 10 times higher than that of diacetyl and most yeast strains produce far less pentanedione than diacetyl. It is detectable at 0.90 mg/l. It is detectable in aroma and flavor as honey or honey-like perfume. Some Vicinal Diketones and reduced derivatives in beer Material Description Detectable range 2, 3-hexanedione Strawberry <0.01 2, 3-pentanedione Honey 0.1-0.15 3-hydroxy-2-pentanone 0.05-0.07 Acetoin Fruity, moldy, woody 1-10 Diacetyl Butterscotch 0.01-0.4 mg/l

Yeast.

? mg/l.

See Ethanol, Esters, Raisin and Sherry-like.

Malt, oxidation.

? mg/l.

See Almond, Malty, Nutty and Oxidized.

? mg/l.

See Ethanol, Fusel Alcohols, Solventy Esters and Spicy.

Recipe, yeast, infection.

? mg/l.

See Body.

? mg/l.

See Hoppy or Phenols (Tannins).

Malt.

? mg/l.

See Grainy, Malty or Sweet.

Yeast, process faults.

?.

Living yeast cells can give beer a distinct flavor and aroma, which is different from the aromas and flavors of autolyzed yeast. All cask-or bottle-conditioned beer will have some yeast in it, but yeast levels are likely to be very low unless the yeast is a non-flocculent strain or the sedimented yeast cake at the bottom of the package is roused. High levels of yeast generally indicate insufficient conditioning time or rough transfer of raw or packaged beer which disturbed the yeast on the bottom of the vessel. Also see Autolysed and Umami.