acetaldehyde
“Acetaldehyde , like emulsion paint or green apples”
Technical specification
Assessment
Cover the beer with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
15 mg Threshold
5 mg / l in beer Origins
Produced by yeast during fermentation. Indicative of fermentation problems and poor control of dissolved oxygen in packaging. Confusions
Ethyl hexanoate
2,4,6-Trichloroanisole
cis -3-Hexenol Importance
Present in all beers. Characteristic flavour of some beer styles, eg Bière de Garde. Off-flavour at high concentrations. CAS registry number
75-07-0 Other names
acetic aldehyde
ethanal
ethyl aldehyde
acetaldehyd
aldehyde acetique
aldeide acetica
octowy aldehyd
Remarks
The flavour impact of acetaldehyde is influenced by the sulphur dioxide concentration in the beer. Threshold distribution
2-acetyl pyridine
“Malty-biscuity , like pale barley malt or malt dust”
Technical specification
Assessment
Without covering the glass, swirl the beer to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
180 µg Threshold
60 µg / l in beer Origins
One of many compounds formed during malt kilning. Such flavours become more prominent in beers which have been contaminated with caustic cleaning agents. Confusions
Sodium bicarbonate
Isobutyraldehyde
Benzaldehyde
Importance
Present in all beers made with barley malt. Desirable flavour in many lagers, ales and stouts. Characteristic flavour of many lagers and ales. CAS registry number
1122-62-9 Other names
2-acetopyridine
2-pyridyl methyl ketone
1-(2-pyridinyl) ethanone
methyl-2-pyridyl ketone
popcorn pyridine
1-pyridin-2-ylethanone
Remarks
2-Acetyl pyridine is one of many similar compounds which are responsible for the range of malty characters found in beer. Threshold distribution
2,3-butanedione
“Diacetyl , like butter, or butter popcorn”
Technical specification
Assessment
Without covering the glass, swirl the beer to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
130 µg Threshold
10 – 40 µg / l in beer Origins
Produced in beer from a precursor formed by yeast during fermentation. Can also be formed by contaminant lactic acid bacteria. Confusions
Butyric acid
Vanillin
Isobutyraldehyde
Importance
Desirable flavour in some ales, stouts and lagers, eg Pilsner. Off-flavour in other lager beers. Considerable efforts are made by breweries to tightly control this flavour character. CAS registry number
431-03-8 Other names
diacetyl
biacetyl
2,3-butane dione
butane-2,3-dione
2,3-diketobutane
dimethyl diketone
dimethyl glyoxal
2,3-dioxobutane
Remarks
2,3-Butanedione is one of two vicinal diketones found in beer. The ratio of diacetyl to pentanedione concentrations can be used as an indicator of bacterial contamination in beer. Threshold distribution
dimethyl sulphide
“DMS , like sweetcorn or tomato sauce”
Technical specification
Assessment
Without covering the glass, swirl the beer to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
150 µg Threshold
30 - 50 µg / l in beer Origins
Formed from malt-derived precursors, primarily during wort production and – to a lesser extent – during fermentation. Confusions
Methyl thioacetate
Ethanethiol
Dimethyl trisulphide
Importance
Desirable flavour in some pale lager beers and ales. Off-flavour in other beers. Excessive levels are indicative of growth of contaminant bacteria during fermentation. CAS registry number
75-18-3 Other names
DMS
dimethyl monosulfide
methylsulfanylmethane
methyl monosulfide
methane thiomethane
methyl sulfide
methyl thioether
methylsulfanylmethane
2-thiapropane
thiobis(methane)
thiobismethane
Remarks
The perception of dimethyl sulphide is influenced by the presence of aromatic higher alcohols such as 2-phenylethanol in beer. Threshold distribution
ethyl acetate
“Ethyl acetate , like nail varnish remover”
Technical specification
Assessment
Cover the beer with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
15 mg Threshold
10 mg / l in beer Origins
Produced by both ale and lager yeast during fermentation. Amount depends on wort composition, yeast strain and fermentation conditions. Wild yeasts produce high levels. Confusions
Acetaldehyde
Ethyl hexanoate
Ethyl butyrate
Importance
Present in all beers, and the ester found in greatest amounts. Its high flavour threshold means that it makes a bigger contribution to the flavour of ales - and especially strong ales - than it does to lagers. CAS registry number
141-78-6 Other names
acetic acid ethyl ester
acetic ether
acetoxyethane
methyl trithiomethane
methylsulfanyldisulfanylmethane
methyltrithiomethane
2,3,4-trithiapentane
methylsulfanyldisulfanylmethane
Remarks
Use two capsules of this flavour standard in each litre of beer to achieve a similar flavour intensity to that achieved using other flavour standards. Threshold distribution
ethyl hexanoate
“Ethyl hexanoate , like apple or aniseed”
Technical specification
Assessment
Cover the beer with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
600 µg Threshold
200 µg / l in beer Origins
Produced by both ale and lager yeast during fermentation. Amount produced depends on wort composition, yeast strain and fermentation conditions. Confusions
Acetaldehyde
Ethyl butyrate
Geraniol
Importance
Present in all beers. Concentrations vary from beer to beer. Key flavour impact character in some lagers and ales. CAS registry number
123-66-0 Other names
butyl acetic acid ethyl ester
capronic ether
ethyl caproate
ethyl hexoate
hexanoic acid ethyl ester
Remarks
Excessive concentrations of ethyl hexanoate are indicative of poor yeast handling in the brewery. Threshold distribution
ferrous sulphate
“Metallic , like ink or blood”
Technical specification
Assessment
Take a little beer into your mouth. Move it around with your tongue for a few seconds then swallow it. To confirm, rub a little of the beer onto the back of your hand and check for metallic odour. Amount of flavour per capsule
8.2 mg Threshold
2.7 mg / l in beer Origins
Derived from contamination of beer with metal ions, either from brewing raw materials or from corrosion of brewery plant. Metallic odours can also be produced by lipid oxidation. Confusions
Sulphitic
Citric acid
trans -2-Nonenal Importance
Taint and occasionally off-flavour in beer. Primarily affects beer mouthfeel but occasionally beer odour can also be affected. CAS registry number
7782-63-0 Other names
ferrous sulfate
iron(2+) sulfate
iron(2+) sulphate
ferrous sulphate heptahydrate
ferrous sulfate heptahydrate
iron(2+) sulfate heptahydrate
iron(II) sulfate heptahydrate
iron(II) sulphate heptahydrate
Remarks
Copper, manganese and tin can also generate metallic notes in beer. Such metals stabilize beer foam and shorten beer flavour life. Threshold distribution
hop oil extract
“Hop oil , like hoppy ale”
Technical specification
Assessment
Without covering the glass, swirl the beer to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
1.25 mg Threshold
250 µg / l in beer Origins
Contributed to beer by addition of hop oils in the brewhouse, fermentation or post-fermentation. The intensity and nature of the character depends on the hop products and brewing practices. Confusions
Kettle hop extract
Geraniol
4-Vinyl guaiacol
Importance
Positive flavour character imparted to specialty ales by addition of hop oil. Different hop varieties in combination with different beers give rise to a variety of hop flavour characteristics. CAS registry number
8007-04-3 Other names
hop oil
target hop extract
hop essential oil
Remarks
Not a reference standard in the strictest sense, since the flavour is derived from a complex natural mixture of many compounds. Threshold distribution
isoamyl acetate
“Isoamyl acetate , like bananas or pear drops”
Technical specification
Assessment
Cover the beer with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
3.5 mg Threshold
1.1 mg / l in beer Origins
Produced by both ale and lager yeast during fermentation. Amount depends on wort composition, yeast strain and fermentation conditions. Confusions
Ethyl hexanoate
Ethyl acetate
Ethyl butyrate
Importance
Present in all beers. Concentrations vary considerably from beer to beer. Key flavour impact character in some lagers and ales. Signature flavour character in German-style wheat beer. CAS registry number
123-92-2 Other names
3-methylbutyl acetate
acetic acid 3-methyl butyl ester
acetic acid isopentyl ester
isoamyl ethanoate
3-methyl butyl acetate
beta-methyl butyl acetate
2-methyl butyl ethanoate
3-methyl butyl ethanoate
3-methyl-1-butanol acetate
3-methyl-1-butyl acetate
3-methylbutyl acetate
isopentyl acetate
isopentyl alcohol acetate
isopentyl ethanoate
Remarks
Disappears during ageing of beer in pack, contributing to a loss of freshness. Threshold distribution
methanethiol
“Mercaptan , like drains or rotting garbage”
Technical specification
Assessment
Without covering the glass, swirl the beer to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
4.5 µg Threshold
1.5 µg / l in beer Origins
Arises through yeast autolysis at the end of fermentation or during maturation. Can also be contributed by dry hopping and by growth of bacteria in beer. Confusions
Ethanethiol
Dimethyl trisulphide
Sulphur dioxide
Importance
Component of the sulphury flavour character of beer. Found in all beer styles to a degree. Off-flavour when present in excess. CAS registry number
74-93-1 Other names
methyl mercaptan
mercaptomethane
methane thiol
methyl sulfhydrate
thiomethanol
thiomethyl alcohol
Remarks
Methanethiol is the main thiol found in beer. Other thiols give similar flavour notes which have subtle differences in relation to their flavour associations. Threshold distribution
3-methyl-2-butene-1-thiol
“Lightstruck , like a skunk or freshly-brewed coffee”
3-methyl-2-butene-1-thiol
100 ng
Technical specification
Assessment
Best detected by smelling the beer at a distance. Hold the glass at arm’s length and take short sniffs to prevent the risk of adaptation. Amount of flavour per capsule
100 ng Threshold
4 – 30 ng / l in beer Origins
Formed as a result of exposure of beer to daylight or artificial light. This initiates a reaction involving hop bitter acids, vitamins and sulphur compounds. Small amounts are also formed in beer production. Confusions
Sulphur dioxide
cis -3-HexenolEthanethiol
Importance
Off-flavour associated with exposure to light of beer packaged in clear or green glass. Consumers are very tolerant of this off-flavour. Many successful beers contain this flavour at the point of consumption. CAS registry number
5287-45-6 Other names
lightstruck
sunstruck
prenyl mercaptan
3-methyl but-2-ene-1-thiol
methyl butene thiol
3-methyl-2-butene-1-thiol
3-methyl-2-butenyl mercaptan
3-methylbut-2-ene-1-thiol
prenyl thiol
Remarks
Beers which have been bittered with chemically-modified hop extracts do not develop this character. Threshold distribution
4-vinyl guaiacol
“Phenolic , like cloves or wheat beer”
Technical specification
Assessment
Cover the beer with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
900 µg Threshold
300 µg / l in beer Origins
Low levels of this flavour are produced during wort production. High levels result from the use of speciality yeast strains or contamination of beer with wild yeasts. Confusions
Isobutyraldehyde
Sulphur dioxide
Vanillin
Importance
Key flavour impact character in some ales and stouts. Off-flavour in lager beers when it is associated with a moderate degree of consumer rejection. Signature flavour character in German-style wheat beer. CAS registry number
7786-61-0 Other names
4-vinyl-2-methoxyphenol
4-ethenyl-2-methoxyphenol
2-hydroxy-3-methoxystyrene
4-hydroxy-3-methoxystyrene
4-hydroxy-3-methoxyvinyl benzene
2-methoxy-4-vinyl phenol
varamol
para-vinyl catechol-ortho-methyl ether
p-vinyl guaiacol
vinylguaiacol
para-vinyl guaiacol
Remarks
4-Vinyl guaiacol (4-VG) is produced by yeasts which possess the phenyl acrylate decarboxylase (PAD) gene. The enzyme associated with this gene produces 4-VG from barley-derived ferulic acid. Threshold distribution
