4-Ethylphenol


4-Ethylphenol is a phenolic compound.

Natural occurrences

In wine and beer, 4-EP is produced by the yeast Brettanomyces. When it reaches concentrations greater than the sensory threshold it can give the wine aromas described as barnyard, medicinal, band-aids, and mousy. In certain Belgian beer styles, a high 4-EP level may be desirable; however, very high levels of the compound in wine can render it undrinkable. The level of 4-EP is roughly proportional to Brettanomyces concentration and activity, and can therefore be used as an indicator of the yeast's presence. There are significant differences between strains of Brettanomyces in their ability to produce 4-EP.
4-EP is also a component of castoreum, the exudate from the castor sacs of the mature North American beaver and the Eurasian beaver, used in perfumery.

Biochemistry

4-EP is produced from the precursor p-coumaric acid. Brettanomyces converts this to 4-vinylphenol via the enzyme cinnamate decarboxylase. 4-Vinylphenol is further reduced to 4-ethylphenol by the enzyme vinyl phenol reductase. Coumaric acid is sometimes added to microbiological media, enabling the positive identification of Brettanomyces by smell.