4-ethyl phenol

400 µg per capsule

Band aid, like a beer contaminated with Brettanomyces

Certified beer flavour standard used to train professional tasters to recognize and scale the intensity of ethyl phenol character. Ethyl phenol is produced by contaminant Brettanomyces yeasts and sometimes by lactic acid bacteria. This compound imparts an unpleasant 'band-aid' note to beer, occasionally described as 'horse-like' or 'barnyard'. At low levels ethyl phenol contributes to product complexity.

Food grade | free from sensory impurities | extensively tested | safe to smell and taste.

Flavour cards

Flavour standard information

Technical specification

The best way to evaluate band aid, horsey flavour notes caused by growth of Brettanomyces in beer is as follows. 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
400 µg per capsule
The flavour threshold of 4-ethyl phenol in beer is 300 µg / l.
4-Ethyl phenol is produced by contaminant Brettanomyces (Dekkera) yeasts and, occasionally by lactic acid bacteria, during beer production. Beers which are low in sulphur dioxide are particularly sensitive to growth of such microorganisms. Produced by Brettanomyces yeasts during or after fermentation. In most beers, Brettanomyces is a contaminant. Ethyl phenol is an off-flavour in such beers. Some beers styles rely on flavours produced by Brettanomyces for their distinctive character.
Since conventional brewer’s yeast (Saccharomyces) does not produce 4-ethyl phenol, its presence in most beers indicates microbiological contamination.
CAS registry number
The CAS registry number for 4-ethyl phenol is 123-07-9.
Other names
  • p-ethyl phenol
  • para-ethyl phenol
  • 1-ethyl-4-hydroxybenzene
  • 4-ethylphenol
  • 1-hydroxy-4-ethyl benzene
  • 4-hydroxyethyl benzene
  • 4-hydroxyphenyl ethane
Sometimes referred to as ‘Band-aid’, this flavour is often found alongside other notes produced by Brettanomyces, including acetic, ethyl acetate, and isovaleric characteristics. ‘Mousy’ flavours are also occasionally produced.
Threshold distribution
Capsules per pot
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