In wine and beer, 4-EP is produced by the yeast Brettanomyces. At concentrations greater than 140 μg/L (typical sensory threshold) it gives the wine aromas described as barnyard, medicinal, band-aids, and mousy.
Brettanomyces yeast is responsible for producing 4-EP, a compound that contributes to the characteristic aromas of wine and beer at concentrations above 140 µg/L.