Ethylphenol (4-EP) is an organic compound with the formula C2H5C6H4OH. It is one of three isomeric ethylphenols. A white solid, it occurs as an impurity in xylenols and as such is used in the production of some commercial phenolic resins. It is also a precursor to 4-vinylphenol.[3]
In wine and beer, 4-EP is produced by the yeastBrettanomyces. At concentrations greater than 140 μg/L (typical sensory threshold) it gives 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 (Castor canadensis) and the Eurasian beaver (Castor fiber), used in perfumery.
