| Colorless liquid|
4-Ethylguaiacol, often abbreviated to 4-EG, is a phenolic compound with the molecular formula C9H12O2. It is produced along with 4-ethylphenol (4-EP) in wine and beer by the spoilage yeast Brettanomyces. When it is produced by the yeast to concentrations greater than the sensory threshold of >600 µg/L, it can contribute bacon, spice, clove, or smoky aromas to the wine. On their own these characters can be quite attractive in a wine, however as the compound usually occurs with 4-EP whose aromas can be more aggressive, the presence of the compound often signifies a wine fault. The ratio in which 4-EP and 4-EG are present can greatly affect the organoleptic properties of the wine.