indole

Technical specification

Assessment

The best way to evaluate indole in beer is as follows. 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. Note that half of all tasters are essentially blind to the concentrations of indole found in beer.

Amount of flavour per capsule

44 µg per capsule

Threshold

The flavour threshold of indole in beer (for the most sensitive half of the population) is 15 µg / l.

Origins

Indole is formed by contaminant ‘coliform’ bacteria during fermentation. It is often associated with simultaneous production of dimethyl sulphide.

Confusions

Professional beer tasters can confuse the flavour of indole with the following flavours:,/p>

• Octanoic acid
• Benzaldehyde
• β-Damascenone

Importance

Indole is an off-flavour in lagers, ales and stouts. It is regarded by some as ‘artisanal’ character (‘jasmine / floral’) and by others as a serious off-note (‘faecal / dirty’).

CAS registry number

The CAS reference number of indole is 120-72-9.

Other names

• 2,3-benzopyrrole
• ketole
• 1-benzazole

Remarks

There are big differences in the perception of individual tasters and consumers to indole. This results in about half of the population regarding indole as a serious fault and half being oblivious to it.

Threshold distribution

Capsules per pot

10

Legal notices

This product is protected by the following trade marks and patents:

• US Patent no. D679900
• European Community Trade Mark
  Registration no. 009937574
• European Community Trade Mark
  Registration no. 009856527
• US Trade Mark Registration no. 4345057
• US Trade Mark Registration no. 4345056