acetic acid
"acetic , like vinegar or spoiled beer"
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
275 mg Threshold
90 mg / l in beer Origins
Produced by yeast during fermentation. Too much yeast growth, contaminating bacteria and wild yeasts can produce excessive levels. Confusions
Citric acid
Lactic acid
Acetaldehyde
Importance
Present in all beers. Characteristic flavour of some beer styles, eg Lambic beer. Off-flavour at high concentrations. Common problem in draught-dispensed beers. CAS registry number
64-19-7 Other names
ethanoic acid
ethylic acid
methanecarboxylic acid
vinegar acid
acetasol
acide acetique
shotgun
vinegar
Remarks
The intensity of this flavour increases with decreasing beer pH value. Threshold distribution
butyric acid
“Butyric“ , rancid, like baby vomit”
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
9.0 mg Threshold
3 mg / l in beer Origins
Produced by bacteria during mashing and sweet wort separation, or during sugar syrup production or storage. Occasionally formed as a result of bacterial spoilage of packaged beer. Confusions
Isovaleric acid
Ethyl butyrate
2,3-Butanedione
Importance
Off-flavour in beer. The flavour of affected beers can be worsened by the presence of 2,3-butanedione, or improved by ethyl butyrate derived from metabolism of butyric acid by yeast. CAS registry number
107-92-6 Other names
butanoic acid
butanic acid
n-butanoic acid
1-butyric acid
n-butyric acid
ethyl acetic acid
1-propane carboxylic acid
propyl formic acid
Remarks
The intensity of this flavour increases with decreasing beer pH value. Threshold distribution
dimethyl trisulphide
“Onion , like fried onion or garlic”
dimethyl trisulphide
130 ng
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
130 ng Threshold
40 ng / l in beer Origins
Although produced from amino acids during wort boiling most dimethyl trisulphide is formed during storage of packaged beer. Some hops impart this character when used post-fermentation. Confusions
Methanethiol
Ethanethiol
Dimethyl sulphide
Importance
Desirable hop-derived flavour note in some ales. Off-flavour formed during ageing of pale lager beers. Can also be found in fresh lager beer as a result of wort boiling practices. CAS registry number
3658-80-8 Other names
DMTS
1,3-dimethyl trisulfane
methyl trisulfide
methyl trithiomethane
methylsulfanyldisulfanylmethane
methyltrithiomethane
2,3,4-trithiapentane
methylsulfanyldisulfanylmethane
Remarks
Recognized as an important contributor to the aged character of pale lager beers. Threshold distribution
ethyl phenylacetate
“Honey , like sweet mead or sherry”
ethyl phenylacetate
480 µg
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
480 µg Threshold
160 µg / l in beer Origins
Formed during ageing of beer. Tends to develop after the appearance of papery, tobacco and leathery notes, and after the loss of banana and bitter notes. Confusions
Importance
Off-flavour formed during ageing in pack from precursors which are formed during fermentation. Positive flavour note in Honey beers. CAS registry number
101-97-3 Other names
benzene acetic acid ethyl ester
ethyl 2-phenyl ethanoate
ethyl 2-phenylacetate
ethyl alpha-toluate
ethyl benzene acetate
ethyl phenyl ethanoate
phenyl acetic acid ethyl ester
alpha- toluic acid ethyl ester
Remarks
This compound is also responsible for the sweet, honey-like off-flavours which develop in some white wines. This flavour note is slow to develop on the palate. Threshold distribution
guaiacol
“Smoky , like smoked fish or cheese”
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
100 µg Threshold
33 µg / l in beer Origins
Contributed to brewing raw materials (malt, rice etc ) by intentional or non-intentional exposure to smoke. Occasionally formed by bacteria during fermentation. Confusions
4-Vinyl guaiacol
Eugenol
2,6-Dichlorophenol
Importance
Off-flavour in pale lager beers. A desirable character in some ales in which it is imparted by speciality malts. Signature flavour character of Rauchbier (smoked beer). CAS registry number
90-05-1 Other names
2-methoxyphenol
anastil
guajacol
guajol
guasol
1-hydroxy-2-methoxybenzene
2-hydroxyanisole
ortho-hydroxyanisole
1-oxy-2- methoxybenzene
ortho- methoxyphenol
methyl catechol
ortho- methyl catechol
pyrocatechol methyl ester
pyrocatechol monomethyl ether
Remarks
A flavour which tends to polarize consumers – they either love it or hate it. Threshold distribution
trans,trans -2,4-heptadienal“Rancid oil , like cod liver oil”
trans,trans -2,4-heptadienal
trans,trans -2,4-heptadienal450 µg
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
450 µg Threshold
150 µg / l in beer Origins
Formed in adjuncts, such as maize, during storage as a result of enzymic or non-enzymic lipid oxidation. Use of such materials can lead to development of this rancid oil flavour note in beer. Confusions
Importance
Off-flavour in beer associated with ageing. Beers made with oil-rich adjuncts are most susceptible to development of this flavour. CAS registry number
4313-03-5 Other names
(2E,4E)-hepta-2,4-dienal
(2trans,4trans)- hepta-2,4-dienal
(E)-2,(E)-4-heptadien-1-al
(E,E)-2,4-heptadien-1-al
trans-2,trans-4-heptadien-1-al
trans,trans-2,4-heptadien-1-al
(E,E)-2,4- heptadienal
Remarks
Common fault in high adjunct pale lager beers made in warm climates. Develops during the early stages of oxidation, before the appearance of papery and leathery notes. Threshold distribution
hydrogen sulphide
“H2 S , like boiled or rotten eggs”
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
18 µg Threshold
4 µg / l in beer Origins
Produced by both ale and lager yeast during fermentation and maturation. Amount depends on wort composition, yeast strain and fermentation conditions. Confusions
Sulphur dioxide
Ethanethiol
Methanethiol
Importance
Present in all beers. Concentrations vary considerably from beer to beer. Off-flavour in most beer styles. Signature flavour character in Burton ale. CAS registry number
7783-06-4 Other names
H2 S
hydrogen sulfide
dihydrogen monosulfide
dihydrogen monosulphide
hydrogen sulfuric acid
hydrogen sulphuric acid
sulfur hydride
Remarks
Can contribute to a perception of ‘freshness’ in beer when present at low levels. Threshold distribution
isobutyraldehyde
“Grainy , like germinating malt”
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
80 µg Threshold
10 - 25 µg / l in beer Origins
Isobutyraldehyde and related compounds can arise in beer through use of pale malts and certain brewhouse procedures. Yeast strain and vigour is also important. Confusions
Acetaldehyde
trans -2-Nonenaltrans,trans -2,4-Heptadienal
Importance
Present in all beers. Concentrations vary from beer to beer. Key flavour impact character in some lagers and ales. Off-flavour in low and non-alcoholic beers. Signature flavour character in some stouts. CAS registry number
78-84-2 Other names
2-methylpropanal
isobutanal
isobutyl aldehyde
isobutyral
isobutyric aldehyde
2-methyl propanal
2-methyl propionaldehyde
alpha-methyl propionaldehyde
2-methyl-1-propanal
2-methylpropanal
isopropyl aldehyde
valine aldehyde
Remarks
Several compounds, closely related to isobutyraldehyde also impart grainy notes to beer. The flavour impact of such aldehydes is influenced by the sulphur dioxide concentration of the beer. Threshold distribution
isovaleric acid
“Isovaleric , like stale cheese or sweaty socks”
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
3.0 mg Threshold
1 mg / l in beer Origins
Derived from breakdown of alpha-acids in hops. Imparted to beer by use of high hopping rates or degraded hops or hop extracts. Can occasionally be produced by wild yeasts. Confusions
Butyric acid
Ethyl butyrate
2,3-Butanedione
Importance
Characteristic flavour of some beer styles, eg India Pale Ale. Typical ‘cheesy’ character associated with beers of very high bitterness. Off-flavour at high concentrations. CAS registry number
503-74-2 Other names
3-methylbutanoic acid
isobutyl formic acid
delphinic acid
dephinic acid
3-methyl butanoic acid
3-methyl butyric acid
beta-methyl butyric acid
3-methylbutanoic acid
isopentanoic acid
isopropyl acetic acid
isovalerianic acid
Remarks
The intensity of this flavour increases with decreasing beer pH value. Threshold distribution
methional
“Methional , like mashed potato or autolysed yeast”
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
17 µg Threshold
5 µg / l in beer Origins
Produced in the brewhouse from breakdown of amino acids. Released during beer ageing. Also associated with re-use of beer recovered from yeast and with over-pasteurization of beer. Confusions
Methanethiol
Dimethyl disulphide
Hydrogen sulphide
Importance
Important ageing character of lager, ales and stouts. Sulphury off-flavour of fresh lager beer. Signature ‘worty’ note in many low- and non-alcoholic beers. CAS registry number
3268-49-3 Other names
beta-methiopropionaldehyde
beta-(methyl mercapto) propionaldehyde
methyl mercaptopropionaldehyde
3-methyl mercaptopropionaldehyde
beta-methyl mercaptopropionaldehyde
methyl mercaptopropionic aldehyde
3-methyl mercaptopropyl aldehyde
3-(methyl thio) propanal
3-(methyl thio) propionaldehyde
beta-(methyl thio) propionaldehyde
3-methyl thiopropionaldehyde
beta-methyl thiopropionaldehyde
3-methylsulfanylpropanal
Remarks
The flavour impact of methional is influenced by both the alcohol and sulphur dioxide concentrations of the beer. Higher concentrations of both compounds suppress its flavour. Threshold distribution
trans -2-nonenal“Papery , like cardboard or oxidized beer”
trans -2-nonenal
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
730 ng Threshold
50 – 250 ng / l in beer Origins
Formed in malt and wort production where it binds to malt proteins. Carried through the brewing process in this bound form. Released during storage of finished beer in pack. Confusions
2,4,6-Trichloroanisole
2-Ethyl fenchol
Isobutyraldehyde
Importance
Off-flavour in beer associated with ageing. Formation of this flavour is more pronounced when precautions have not been taken in relation to minimizing process oxidation. CAS registry number
18829-56-6 Other names
(E)-heptylidene acetaldehyde
(E)-3-hexyl acrolein
(E)-3-hexyl-2-propenal
(E)- non-2-enal
trans-non-2-enal
(E)-2-nonen-1-al
trans-2-nonen-1-al
(E)-2- nonenal
trans-2- nonenal
Remarks
Sulphur dioxide in beer reversibly reacts with trans-2-nonenal to reduce its flavour impact. Threshold distribution
styrene
“Plastics , like polystyrene”
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
65 µg Threshold
20 µg / l in beer Origins
Produced by contaminant wild yeasts during fermentation. Can taint product through use of contaminated packaging materials or defective carbon dioxide gas. Confusions
Acetaldehyde
4-Vinyl guaiacol
Eugenol
Importance
Off-flavour or taint in beer. Associated with a moderate degree of consumer rejection. Often described by consumers as ‘chemical’, ‘plasticy’ or ‘contaminated’. CAS registry number
100-42-5 Other names
ethenylbenzene
phenyl ethene
phenyl ethylene
styrol
styrolene
vinyl benzene
vinyl benzol
Remarks
Other compounds can impart a plastic-like note to beer. Samples containing this standard are best tasted in glass, rather than in plastic, to avoid loss of odour. Threshold distribution
