Troubleshooting
– Off Flavors in Beer
Analysis
of Flavor
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ACETALDEHYDE
CHARACTERISTICS: Acetaldehyde is the flavor and aroma of green apples. It can
also taste and smell acetic/cidery.
CHEMISTRY: Formed as a precursor to alcohol by the yeast, or as a product of
the oxidation of alcohol to acetic acid.
CAUSES: Yeast metabolism (fresh-cut apples) uses acetaldehyde as a step in the
production of alcohol from glucose. This is a fresh, fruity flavor. The second
cause is the oxidation of alcohol to acetic acid, whether by oxidation or by acetobacter (gram-negative). This flavor will be more
vinegary and less pleasant.
PROCESS: As a product of yeast metabolism, it can be caused by the strain
itself or by premature termination of the yeast’s fermentation, such as oxygen
depletion, premature flocculation, etc. such that the reaction from glucose to
alcohol is stopped at the acetaldehyde stage.
The other causes are oxidation and contamination by acetic acid bacteria. This
will occur during splashing when racking quiet beer (non-kraeusened)
and bottling.
REMOVAL: Use a good yeast strain that will attenuate the wort
properly. Oxygenate the wort at yeast-pitching time.
DO NOT splash or oxygenate the wort when racking or
bottling. Long lagering periods will also reduce
acetaldehyde.
EXAMPLES: Budweiser deliberately manipulates their yeast and process to give
6-8 ppm acetaldehyde in the beer.
ALCOHOLIC
CHARACTERISTICS: Both an aroma and a mouth-feel. A hot, spicy flavor detected
by the nose as a vinous aroma and by the tongue by a warming sensation in the
middle of the tongue. A warming, prickling sensation in the
mouth and throat.
CHEMISTRY: The end product from the conversion of glucose into carbon dioxide
and ethyl alcohol. Other, higher alcohols can also be present. These are called
fusel oils and contribute to vinous aromas and tastes.
CAUSES: A normal reaction desired in beer, alcohol content is a function of the
amount of fermentable sugars in the wort, the
fermentation temperature, and the yeast strain.
Fusel oil production will be a function of the yeast strain used and the
fermentation temperature (higher temperatures give more fusel oils).
PROCESS: Amount and types of fermentables in wort determine content; yeast strain and attenuation
characteristics; fermentation temperature determines fusel oil characteristic.
REDUCTION: The amount of alcohol and fusel alcohols should be appropriate for
the beer style. Control alcohol by wort
start gravity and wort content (avoid large amounts
of sugars). Wort should attenuate to about 1/4
of starting gravity.
Control fusel oils by using colder fermentation temperatures.
EXAMPLES: High, lots of fusel oils: Thomas Hardy’s;
Moderate fusel oils: British Bitter; Low fusel oils: Pilsner Urquell.
ASTRINGENT
CHARACTERISTICS: Unlike bitterness, astringency is present as a stimulation of
the nerve endings throughout the mouth. It is not an aroma. The taste is a
puckering, dry, unpleasant situation. It is a very acidic, tannic, tart
sensation reminiscent of grape skins.
CAUSES: Bacterial contamination (lactobacillus and acetobacter);
added astringency from grains or hops.
PROCESS: Caused by: poor sanitation; excessive hopping; excessive wort attenuation (small dextrin content) giving greater
perception of astringent; boiling grains; excessive grain crushing; too high a lauter run-off temperature (170 degrees max); to much
run-off in lautering; letting beer sit too long on trub; non-blowoff primary
fermentation; alkaline mash or runoff water; too much sulfate, magnesium or
iron; excessively high acidity.
REDUCTION: Process changes to eliminate the above. Crack grain properly, watch
mash/runoff pH, 170 degrees maximum for lauter runoff
water, use blowoff fermentation; good sanitation
practice.
EXAMPLES: Young wine and grape skins; blowout from primary fermentation.
BITTER
CHARACTERISTICS: Generally a desired characteristic of hop use. Bitterness will
be tasted on the back of the tongue and the roof of the mouth. One of the four basic tastes.
CAUSES: Hop content and alpha strength; length of hop boil; presence of dark
malts, alkaline water.
PROCESS: How long hops are boiled, type of hop,
fermentation temperature (high temperature and quick fermentation decrease
bitterness), filtration reduces bitterness.
REDUCTION: Lower alpha hops, hops added at stages through boil, filtration,high temperature
ferment.
EXAMPLES: Bittering hop extract in water will
sensitize you to bitterness.
BODY
CHARACTERISTICS: Mouth feel (will feel full). A sensation of
viscosity in the mouth.
CHEMISTRY: Caused by polysaccharides (dextrins) in
the beer that are unfermentable
by the yeast.
CAUSES: Caused by presence of unfermentable
sugars or dextrins.
INCREASE: Desired in beer. High-temperature saccharification
rest in mash;use of crystal
malt and cara-pils malts; use of malto-dextrin,
use of lactose.
REDUCTION: Generally not desired. Use of low-temperature saccharification
rest in mash, highly-fermentable wort, use of large
amounts of corn sugar in wort, long storage,
bacterial breakdown, not boiling wort that may have
diastase enzymes present.
EXAMPLES: Low: "lite" American beers; High:
Samuel Adams
CLARITY
CHARACTERISTICS: Visual clarity in beer contributes to its appeal and increases
points given in competitions.
INCREASE: Use of well-flocculating yeast strains; clearing agents such as polyclar, papain, Irish moss, bentonite, gelatin, etc.; filtration; long, vigorous boil
and quick chilling; lagering and aging.
DECREASE: Poor, wrong, weak or mutated yeast strains, some ale yeasts, wheat
malt, unmalted barley, poor cold break, poor starch
conversion in mash, poor malt crush with lots of flour, bacterial
contamination, wild yeast contamination, all-malt beer, high protein content
due to ineffective proteolytic rest (especially with undermodified malts), tannin present in beer due to
excessive or high temperature sparge.
EXAMPLES: Clear - any American commercial beer; Cloudy - wheat beers
COLOR
CHARACTERISTICS: As appropriate for style. Properly colored beers win more
points in competitions.
LIGHTER: Use of pale malts, use of sugar or other starchy adjuncts, filtration.
DARKER: Use of higher-temperature kilned malts, use of crystal malt, use of
dark malts, carmelization of the boil, oxygenating
hot wort.
EXAMPLES: Light: Coors Light; Amber: Sam Adams; Dark: Celebrator or Guinness.
CARBONATION
CHARACTERISTICS: The presence of carbonic acid in beer gives the head and
bubbles when the bottle is opened and pressure released. Gives head
characteristic. Taste is tart and acidic, increasing with the carbonation. This
is especially noticeable on overcarbonated brews. An
overall prickly or stimulating mouth feel. Small bubbles are desired, as these
will retain both the head and the carbonation for a longer period.
CAUSES: CO2 from the fermentation process or from bacterial action dissolved in
the beer gives carbonation.
TOO MUCH: Excessive priming sugars, bacterial contamination, presence of
amylase enzymes in bottled beer, iron or calcium oxalate in the water, isomerized hop extract, autolyzed
yeast sediment, excessive starch, not boiling extract worts,
fusarium mold on barley or in extract, precipitation
of excess salts in the bottle.
TOO LITTLE: Poor bottle cap seal, not enough priming sugar, weak or dead yeast
culture when bottling (as from long lagering
periods).
EXAMPLES: Highly carbonated: Wheat beers; low: English bitters.
DIACETYL
CHARACTERISTICS: A butterscotch aroma and taste, and a
slickness on the palate. Not desired in excessive quantities.
CAUSES: A normal product of yeast during fermentation, it is re-absorbed during
the course of a normal fermentation. Another cause is the gram-positive
bacterium Pediococcus cerevisiae
and similar strains in cooled beer, young beer, and aging beer. Lactobacillus
strains in the mash can also cause this flavor if the mash held at low
temperatures (below 131 degrees). Note that the aroma/taste produced by all of
these causes is indistinguishable.
CHEMISTRY: One of a family of vicinal diketones.
Presence recognized down to 0.05 ppm, but identified
at 0.15 ppm.
HIGH RATES FROM PROCESS: Underpitching of yeast; long
periods of wort cooling (overnight); contamination from
equipment; poor yeast strain; too-soon clearing (fining) of yeast (before it
can reabsorb the diacetyl); too long an acid rest in
mash; high adjunct ratio in wort; low fermentation
temperature; premature lagering; any process that
stimulates yeast then immediately removes it from suspension; use of
contaminated sediment for re-pitching (bacteria coexists with yeast in the
sediment).
REDUCTION: Sanitation, quick wort chilling combined
with adequate yeast starter amount (8 ounces of slurry to 5 gallons), adequate
time for primary ferment before lagering or
fining/filtering, all-malt recipe, higher temperature primary fermentation,
pure yeast culture, washing yeast sediment prior to repitching.
EXAMPLES: HIGH: contaminated homebrew; MODERATE: Sam Smith’s Nut Brown Ale,
Pete’s Wicked Ale.
DMS AND SIMILAR COMPOUNDS
CHARACTERISTICS: Volatile sulfur-based compounds that can give beer a taste and
aroma of cooked corn, celery, cabbage or parsnip to almost oystery-shellfish-like
in high concentrations. These include dimethyl
sulfide (DMS), diethyl sulfide, and di-isopropyl
sulfide. DMS is first perceived in aroma at around 30 ppb, and the other
compounds at considerably lower concentrations. These compounds are undesirable
in beer in high amounts.
CAUSES: Wort bacteria (Obesumbacterium or Hafnia) is a major cause, especially of DMS. Coliform bacteria strains can also give a strong
cooked-vegetable note. Additionally, these compounds can be formed during the
kilning of green malt and during mashing. DMS is also formed by the yeast in a
normal fermentation, and during slow cooling of the wort
by a non-microbiological chemical reaction.
HIGH LEVELS DUE TO PROCESS: Poor sanitation (primary cause); not boiling the wort for at least one hour; long cooling times (overnight)
before pitching; underpitching; contaminated yeast
(especially packet yeast and recovered sediment); high moisture malt; over-sparging with water below 160 degrees.
REDUCTION: Good sanitation; fresh yeast culture; good one hour or more rolling boil;
quick wort cooling; high pitching rates; use of 2-row
English malt; proper sparging.
EXAMPLES: Contaminated homebrew.
FRUITY-ESTERY
CHARACTERISTICS: Aromatic compounds that are identified as fruity and estery in higher amounts. The flavor and aroma of fruits
such as strawberry, grapefruit, banana, raspberry, apple and pear and others
can appear in beer due to these esters. Depending on the style, this can be a
desired flavor or one totally unsuitable. Ales and high gravity beers are high
in fruity-estery content, while pilsners and American
lagers are low.
CHEMISTRY: A by-product of fermentation produced by the yeast. Fruity-estery characteristics increase with fermentation
temperature.
INCREASE DUE TO PROCESS: Yeast strain used, higher fermentation temperatures,
fermenting some lager yeasts at temperatures above 50 degrees, high-gravity wort.
DECREASE DUE TO PROCESS: Yeast strain used, fermenting ales around 60 degrees
or less, lagers around 50 degrees or less, lower
gravity wort.
EXAMPLES: High: Old Nick Barley Wine; Low: Coors.
GRASSY
CHARACTERISTICS: The aroma and flavor of fresh-cut grass
CHEMISTRY: The aldehyde called Hexenal,
which is detectable in concentrations of 0.2 ppm.
INCREASE DUE TO PROCESS: Poor quality malt, poor storage of malt, cracking
grains well in advance of brewing
DECREASE DUE TO PROCESS: Good, fresh malt stored under airtight conditions;
cracking grains the day you brew or the night before.
EXAMPLES: Fresh-cut grass
HEAD RETENTION
CHARACTERISTICS: Good head on the beer when poured, not excessively large or
small, Belgian lace on glass, head remains for a long time. Very
much desired.
CAUSES: Small bubbles, dextrins, high molecular
weight proteins, isohumulones from hops, nitrogen in wort.
GOOD HEAD FROM PROCESS: Use of cara-pils; use of
crystal malt; use of malto-dextrin; all-malt beer;
good one hour rolling boil to extract the isohumulones
from the hops; use of extracts, especially those designed for use with sugar
(but using malt instead of sugar); use of wheat malt; adequate protein rest in
mash to allow the proteolytic enzymes to break down
the large proteins into albumin and smaller fractions and increase the
nitrogen; high-temperature saccharification rest;
racking to secondary to get beer off sediment; lower temperature fermentation;
bottle conditioning.
POOR HEAD FROM PROCESS: Use of fully modified malts; use of underkilned
malts; not using a one-hour boil; inadequate protein rest, low-temperature saccharification rest; oversparging;
yeast autolysis from long sediment contact; excessive fusel oils; higher
temperature fermentation; excessive fatty acids; overboiling
of wort; insufficient or deteriorated hops; some
finings.
POOR HEAD WHEN SERVING: Soap, detergent or oils on glasses; lip balm, Chapstick or lipstick on lips.
EXAMPLES: HIGH: Wheat beer; LOW: English bitter, especially cask-conditioned.
HUSKY-GRAINY
CHARACTERISTICS: A taste spectrum that includes astringent tastes, cereal or
grainy tastes, and husky tastes. Generally the grainy notes may or may not be
desirable, depending on the style, but the husky astringent tastes are
undesired. Husky-grainy is generally perceived as a taste, although grain notes
can be present in the aroma.
CAUSES: Tannins from grain husks causes the astringent huskiness, while the
graininess comes from the starches in the barley malt.
INCREASE DUE TO PROCESS: Excessive grain crushing; powdering the malt during
crushing; sparge temperature in excess of 170
degrees; excessive sparging; high pH during sparging (above 6.0); boiling grains; improper decoction
mashing; improper wetting of grist during mash-in; direct-firing of mash tun without proper stirring; old beer; too many salts in
water (sodium, magnesium, sulfate, chloride); iron in water.
DECREASE DUE TO PROCESS: Proper crush; slow mash-in; lautering
temperatures between 164-170 degrees; monitoring pH of runoff and adding gypsum
to keep pH below 6; proper sparge amounts;
temperature controlled or infusion mash; steeping adjunct grains (such as crystal
malt added to extract brews) below 170 degrees instead of bringing to boil;
water appropriate to style; iron-free water.
EXAMPLES: Grainy (appropriate): Stoneys, many
Midwestern regional lagers
LIGHT-STRUCK
CHARACTERISTICS: Skunk odor; unmistakable; smells like a road kill skunk;
tastes like it smells. Totally undesirable in beer.
CHEMISTRY: Light will change some of the hop content of the wort
to skunklike sulfuric compounds.
HIGH CONTENT: Light-struck fermenter; clear or green
glass bottles; sunlight on brown bottles; bar cooler fluorescent lights on
green or clear bottles.
REDUCTION OR ELIMINATION: Fermenter shielded from
light; brown or opaque bottles opaque to 400-520 nm light wavelengths; isomerized hop extract; storing beer in a cool, dark place.
EXAMPLES: Any green-bottle Eurolager left in sun for
15 minutes. =
METALLIC
CHARACTERISTICS: A harsh, metallic taste noted both on the tip of the tongue
and the roof of the mouth. Can be felt throughout the tongue
and mouth in large concentrations. Not desired in beer. Also described as tinny or bloodlike.
CHEMISTRY: The ferrous ion (iron) and some organic compounds formed by
hydrolysis of cereal lipids in grain, and oxidization of free fatty acids.
HIGH RATE FROM PROCESS: Iron or mild steel in contact with beer;
freshly-scrubbed stainless steel that has not been allowed to oxidize; improper
filtering material; high iron content in water; poorly processed grain.
REDUCTION: Use of stainless steel; low-iron water; use of citric acid to
re-oxidize stainless that has been abrasively cleaned; use of filtering
materials that are acid-washed to remove iron; use of fresh, high-quality grain
malt.
MOLDY
CHARACTERISTICS: A cellarlike, damp-earth, rank cabbagy or moldy bread odor. Not a common defect in beer.
CAUSES: Fungal contamination.
CAUSES DUE TO PROCESS: Secondary fermentation or transferring beer in a moldy
environment, like a cellar. Secondary fermentation or lagering in a moldy cellar where the temperature fluctuates
and permits air to be drawn into the carboy. Poor
sanitation.
REMEDIES: Only expose beer to the air for transferring in a reasonably clean
environment. Moldiness smelled in the air is a good indication of an
unacceptable environment. Constant-temperature secondary or lagering environment (to prevent air entering carboy).
Good sanitation practice.
NUTTY
CHARACTERISTICS: An aroma of Brazil nuts, hazelnuts, almonds, or slightly
sherry-like. Not necessarily a defect, unless excessive or inappropriate for
the style.
CAUSES: A product of oxidization or prolonged overheating during aging or after
bottling.
CURES: Store beer in a 55 degree or less cellar; prevent oxidization or
splashing when bottling or racking.
OXIDATION
CHARACTERISTICS: Cardboard, paper, wet paper, sherry-like, rotten fruit,
garbage are all characteristics of oxidation, perceived both as an aroma and a
flavor.
CAUSES: Oxidation of beer and the alcohol component into fusel alcohols,
trans-2-nonenal, acetaldehyde.
HIGH LEVEL: Aeration of beer when transferring or bottling; excessive head
space in bottle; poorly functioning air lock; excessive age; high storage
temperatures; widely-varying secondary or lagering
temperatures; adding tap water to finished beer.
LOW LEVEL: Quiet transfer of beer when siphoning and bottling; flushing out
bottles and kegs with CO2 before filling and capping; cool (<55 degree)
storage of bottled beer; proper head space in bottle; use of ascorbic acid;
good airlock; constant-temperature secondary/lagering;
adding only boiled/chilled water to beer after primary fermentation.
PHENOLIC
CHARACTERISTICS: A hospital-medicine chest flavor and aroma, best detected by
its aroma components; caused by phenols. Some phenolic
tastes are desired depending on the style. Other descriptions include
Band-Aid-like, plasticlike, smoky, clovelike.
HIGH LEVELS DUE TO PROCESS: Yeast strain; chlorophenols
in the water; improper rinse of chlorine sanitizers; oversparging;
sparging above pH 6.0; sparging
above 170 degrees; wild yeast contamination.
LOW LEVELS DUE TO PROCESS: Charcoal filtering of tap water; good healthy yeast
strain; proper sparging while monitoring temperature
and pH, good rinse of sanitizers or use of non-chlorine sanitizers.
EXAMPLES: Wheat beers have a high amount of the phenol 4-vinyl guaiacol that gives the characteristic clove taste.
SALTY
CHARACTERISTICS: Salty is one of the four basic tastes. Saltiness will be found
on the tongue, to either side just behind the tip. Excessive saltiness is not
desired in beer for the most part, but fair quantities will be a characteristic
of Dortmunder lagers and
CHEMISTRY: From sodium chloride and magnesium sulfate and other mineral salts.
HIGH LEVEL FROM PROCESS: Excessive addition of Burton salts or table salt or
Epsom salts, especially adding these to water already high in mineral salts;
water high in sodium chloride or magnesium sulfate.
LOW LEVEL: Use salt-free water; don’t use or use smaller
amounts of added salts, especially
EXAMPLES: High salty mineral content: Bass ale; Dortmunder
lagers.
Low: Pilsner Urquell
SOLVENTLIKE
CHARACTERISTICS: An acetone-like, laquer-thinner-like,
pungent, acrid aroma which is followed up by a harsh, burning sensation on the
tongue and possibly the back of the throat.
CHEMISTRY: Ethyl acetate in larger quantities (>33 ppm)
is the primary cause, either by wild yeast or the yeast strain used. Other
compounds may also be present.
HIGH LEVELS DUE TO PROCESS: Wild yeast contamination due to poor sanitation;
high fermentation temperature; non-food grade plastic equipment in contact with
the beer; open fermenter, especially after high kraeusen subsides; excessive oxygenation of the wort before pitching; oxygen in secondary fermenter.
LOW LEVELS DUE TO PROCESS: Good sanitization of equipment; only food-grade
plastic used; cooler fermentation temperatures; proper wort
oxygenation; closed fermenter.
SOUR-ACIDIC
CHARACTERISTICS: Another of the basic tastes. This is perceived on the sides of
the tongue towards the back of the mouth. At higher levels it can be felt all
the way down the throat. Generally in beer this is perceived as a sour aroma
and a tartness or vinegarlike aroma. Bacteria
contamination sourness can also be perceived as spoilage or putrefaction.
CHEMISTRY: Caused by lactobacillus, pediococcus, acetobacter and some yeast strains.
HIGH CONTENT DUE TO PROCESS: Poor sanitization; bad yeast strain; too much corn
sugar; excessive amounts of citric or ascorbic acid; high fermentation temperatures;
excessive acid rest; mashing too long; use of wooden spoon in cooled wort or fermentation; storage at warm temperatures;
scratched plastic fermenter.
LOW CONTENT DUE TO PROCESS: Good sanitization; stainless steel equipment and
spoons; cool fermentation temperatures; cool beer storage; mashing for not more
than two hours; glass carboy fermenter.
SULFURY-YEASTY
CHARACTERISTICS: Strong sulfuric aroma and taste reminiscent of rotten eggs(hydrogen sulfide), sulfur dioxide, or yeast. Other
descriptions include garlic, burnt rubber, shrimp-like, meaty.
CHEMISTRY: Formed by amino acids methionine and cysteine in the malt and by certain yeast strains and
bacteria, notably Zymononas, Pectinatus,
and Megasphaera. Also formed by
yeast autolysis.
HIGH LEVEL IN PROCESS: Yeast strain; rapid temperature changes to fermenting wort; bacterial contamination; beer left on sediment; wild
yeasts; high fermenter back pressure; poor
oxygenation of wort at yeast-pitching time; use of metabisulfite in beer; old beer (yeast autolysis).
LOW LEVEL IN PROCESS: Good yeast strain; good sanitation practice; racking off
sediment before lagering; cooling lagers no more than
5 degrees per day; cold-pitching lagers; strong, healthy active primary
fermentation (scrubs out the gaseous sulfur compounds).
SWEET
CHARACTERISTICS: One of the four basic tastes, on the tip of the tongue. Desirability dependent on the beer style.
HIGH LEVELS FROM PROCESS: Quick flocculating or low attenuating yeast strain;
lack of yeast nutrients in wort; poor ferment due to
lack of oxygen, yeast nutrient or other flaws; higher gravity wort with low-alcohol tolerant yeast; addition of crystal
malt or licorice; high-temperature mash; addition of dextrin malt or malto-dextrin combined with a quick fermentation; addition
of sugar and pasteurization; addition of lactose; premature lagering.