geosmin

geo·smin | \ jē-ˈō-smən

, ˈjē-ō- \

plural geosmins

Definition of geosmin

: a volatile, organic compound C₁₂H₂₂O that is formed especially by soil-dwelling bacteria (such as streptomyces) and aquatic cyanobacteria and that may contribute to the earthy, pleasant odor of petrichor or impart a disagreeable, musty taste and odor to drinking water and certain fish In the test kitchen, we too have noticed a mysterious muddy flavor in some catfish and tilapia. … When the fish swim in the geosmin-rich water, they consume the compound as they ingest the algae. — Cook's Illustrated Geosmin can be detected by a human nose at miniscule concentrations, as low as just a few parts per trillion, [Kelley Dearing] Smith said.— James Bruggers

Note: Geosmin is a tertiary alcohol having a hydroxyl group (-OH) attached to a carbon atom that has three other carbon atoms attached to it.