benzaldehyde
“Almond , like bitter almonds or marzipan”
Technical specification
Assessment
Cover the sample 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
1.5 mg Threshold
500 µg / l in water Origins
Derived from the breakdown of organic material and through the action of microorganisms, including Actinobacteria, Pseudomonads and algae. Importance
Imparts a pleasant, but nevertheless atypical, sweet odour to water, reminiscent of almonds or marzipan. CAS registry number
100-52-7 Other names
benzene carbaldehyde
benzene carbonal
benzene carboxaldehyde
benzene methylal
benzoic aldehyde
benzoyl hydride
bitter almond oil
phenyl methanal
Remarks
In plant material, benzaldehyde is derived from enzymic breakdown of amygdalin. Threshold distribution
2-bromophenol
“Bromophenol , inky, like a museum or old TV set”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
2.0 µg Threshold
50 ng / l in water Origins
Produced through reaction of phenolic compounds (for example from waters associated with peaty soils) and free bromine. Can also arise due to trace contamination of water with wood preservatives and fire retardants. Importance
Imparts an unpleasant ‘tainted’ note. Described by consumers as ‘chemical’ or ‘contaminated’, even at low levels. CAS registry number
95-56-7 Other names
bromophenol
o-bromophenol
ortho-bromophenol
Remarks
Water pH is important in determining the rate of formation. Can occasionally be produced by bacteria in combination with compounds such as guaiacol. Threshold distribution
β-cyclocitral
“Tobacco-like , like grass, hay or dry wood”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
440 µg Threshold
150 ng / l in water Origins
Formed by Cyanobacteria in reservoirs or water distribution systems. Produced by both actively-growing organisms and through cell lysis or decomposition. Importance
Imparts an aromatic odour, reminiscent of hay and dry wood at low concentrations, becoming more tobacco-like and fruity at higher concentrations. CAS registry number
432-25-7 Other names
beta-cyclocitral
2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde
2,6,6-trimethyl cyclohexene-1-carbaldehyde
2,6,6-trimethyl-1(2)-cyclohexen-1-carboxaldehyde
2,6,6-trimethylcyclohexene-1-carbaldehyde
Remarks
Associated with cases of algal bloom in lakes and reservoirs. May occur together with other carotenoid breakdown products such as Β-ionone. Threshold distribution
dimethyl sulphide
“DMS , like sweetcorn or tomato sauce”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
60 µg Threshold
20 µg / l in water Origins
Formed by bacteria growing in water. Can also arise from decomposition of algae following an episode of algal bloom. Importance
Associated with sulphury and ‘muddy’ odours notes. The presence of DMS can also be indicative of contamination of the water supply chain with faecal bacteria. 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
Indole and skatole may often be found in water in which the DMS has been produced by bacteria. 2-Pentanone may be present in water in which the DMS has been formed by algae. Threshold distribution
dimethyl trisulphide
“Onion , like stagnant water or decaying vegetation”
dimethyl trisulphide
330 ng
Technical specification
Assessment
Cover the sample 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
330 ng Threshold
110 ng / l in water Origins
Formed through decay of grass and vegetation in reservoirs and lakes and by bacterial action. Can also arise from decomposition of algae following an episode of algal bloom. Importance
Imparts an unpleasant ‘swampy’ odour to water. The intensity of the odour can be increased by the presence of other sulphur compounds. 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
Often found in association with other sulphur compounds such as H2 S and methanethiol. Threshold distribution
cis -3-hexenol“Freshly cut grass , like hedge cuttings”
cis -3-hexenol
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
2.9 mg Threshold
950 µg / l in water Origins
Derived from leaching of chemicals from grass and vegetation, and from growth of algae. The compound is produced in plants through the action of the enzyme lipoxygenase. Importance
Imparts a pleasant, but nevertheless atypical, grassy note to water. Often occurs in association with cis-3-hexenyl acetate. CAS registry number
928-96-1 Other names
(Z)-hex-3-en-1-ol
cis-hex-3-en-1-ol
(Z)-3-hexen-1-ol
beta,gamma-hexen-1-ol
cis-3-hexen-1-ol
(Z)-3-hexenol
cis-3-hexenol
beta-gamma-hexenol
leaf alcohol
Remarks
This compound is unstable at high pH values and does not survive well in alkaline waters. Threshold distribution
hydrogen sulphide
“H2 S , like boiled or rotten eggs”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
18 µg Threshold
4 µg / l in water Origins
Formed by anaerobic sulphate-reducing bacteria from sulphate, by Clostridium or Bacillus from sulphite or proteins, or by electrochemical action through corrosion of pipes in systems with very low flow rates. Importance
Imparts an unpleasant sulphury note to water. H2 S is easily oxidized to less odour-active species, so its presence is indicative of the failure of water treatment processes or post-treatment contamination. 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
Often found in association with other sulphur compounds such as methanethiol and dimethyl trisulphide. Be careful not to overexpose yourself to samples with H2 S. The more you look for it the less likely you are to find it. Threshold distribution
indole
“Indole , like pigs on a farm”
Technical specification
Assessment
Cover the sample 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
60 µg Threshold
20 µg / l in water Origins
Formed by bacteria growing in water, or contributed, pre-formed, by ground water pollution. Importance
In addition to contributing an unpleasant farmyard note, the presence of indole can also indicate contamination of the water supply chain with faecal bacteria. CAS registry number
120-72-9 Remarks
DMS and skatole may often be found in water which contains indole. Big differences in perception of individual tasters result in about half regarding this flavour as a serious fault and half being oblivious to it. Threshold distribution
β-ionone
“Violets , like Turkish delight”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
40 µg Threshold
13 µg / l in water Origins
Formed by algae or Cyanobacteria growing in water and through the biochemical decay of grass and vegetable matter in lakes and reservoirs. Importance
Imparts a pleasant, but nevertheless atypical, sweet aromatic odour to water, reminiscent of violets. Derived from the breakdown of plant-derived carotenoids. CAS registry number
14901-07-6 Other names
ionone
beta-cyclocitrylidene acetone
beta-irisone
4-(2,6,6-trimethyl cyclohex-1-ene-1-yl) but-3-ene-2-one
4,2,6,6-trimethyl-1-cyclohexen-1-yl-3-buten-2-one
4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-buten-2-one
4-(2,6,6-trimethyl-1-cyclohexenyl)-3-buten-2-one
(E)-4-(2,6,6-trimethyl-1-cyclohexenyl)but-3-en-2-one
Remarks
Associated with cases of algal bloom in lakes and reservoirs. May occur together with other carotenoid breakdown products such as Β--cyclocitral Threshold distribution
methanethiol
“Mercaptan , like drains or rotting garbage”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
1.0 µg Threshold
330 ng / l in water Origins
Formed by anaerobic sulphate-reducing bacteria and Cyanobacteria or by decay of grass or algae in lakes or reservoirs. Can also arise from decomposition of algae following an episode of algal bloom. Importance
Imparts an unpleasant sulphury note to water. Methanethiol is easily oxidized to less odour-active species, so its presence is indicative of the failure of water treatment processes or post-treatment contamination. CAS registry number
74-93-1 Other names
methyl mercaptan
mercaptomethane
methane thiol
methyl sulfhydrate
thiomethanol
thiomethyl alcohol
Remarks
Often found in association with other sulphur compounds such as H2S and dimethyl trisulphide. Be careful not to overexpose yourself to samples with methanethiol. The more you look for it the less likely you are to find it. Threshold distribution
skatole
“Skatole , like animal faeces”
Technical specification
Assessment
Cover the sample 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
2.0 µg Threshold
700 ng / l in water Origins
Formed by bacteria growing in water, or contributed, pre-formed, by ground water pollution, being produced by bacteria from tryptophan. Importance
In addition to contributing an unpleasant, somewhat nauseating, faecal note to water, the presence of skatole can also indicate contamination of the water supply chain with faecal bacteria. CAS registry number
83-34-1 Other names
beta-methyl indole
β-methylindole
scatole
skatol
3-methylindole
3-MI
3-methyl-1H-indole
3-methyl-4,5-benzopyrrole
Remarks
Indole and DMS may often be found in water which contains skatole. Threshold distribution
2,4,6-trichloroanisole
“Musty , like corked wine or a damp cellar”
2,4,6-trichloroanisole
73 ng
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
73 ng Threshold
<10 - 30 ng / l in water Origins
Derived from methylation of chlorophenols by moulds or Actinobacteria, primarily in water distribution systems. Importance
Imparts an unpleasant musty odour to water which is reminiscent of damp cellars or corked wine. CAS registry number
87-40-1 Other names
methyl 2,4,6-trichlorophenyl ether
1,3,5-trichloro-2-methoxybenzene
TCA
Remarks
2,4,6-Trichloroanisole is one of several chloroanisoles that can taint water. The flavour produced by this compound is typical. This compound can be detected, but not recognized at concentrations well below the recognition flavour threshold. Threshold distribution
