geosmin

noun

geo·​smin jē-ˈō-smən 

ˈjē-ō-

plural geosmins

: 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.

Examples of geosmin in a Sentence

Recent Examples on the Web

Humans are remarkably sensitive to the smell of geosmin, in particular. —Tom Hawking, Popular Science, 12 June 2025

There’s one unanswered question here, though: why are geosmin and 2-MIB there in the first place? —Tom Hawking, Popular Science, 12 June 2025

The scent is a blend of volatile plant oils and the organic compound geosmin, which is released from the soil into the air, along with ozone carried by downdrafts. —Brandi D. Addison, Austin American-Statesman, 22 Apr. 2024

In these field experiments and in the lab, the pungent geosmin, and another compound called 2-methylisoborneol (2-MIB), released by the Streptomyces colonies attracted tiny, six-legged arthropods called springtails in droves, the researchers report last week in the journal Nature Microbiology. —Alex Fox, Smithsonian Magazine, 17 Apr. 2020

The geosmin and other petrichor compounds that may be present on the ground or dissolved within the raindrop are released in aerosol form and carried by the wind to surrounding areas. —Tim Logan, Discover Magazine, 28 Aug. 2018

But Stensmyr and colleagues then had the flies choose between plain yeast and S. coelicolor that couldn’t produce geosmin. —Guest Blogger, Discover Magazine, 7 Mar. 2013

Horticultural scientists have been examining geosmin levels of various beet varieties to breed specialty beets with less of this aromatic compound, such as the Badger Flame varieties developed at the University of Wisconsin. —Casey Barber, CNN, 23 Sep. 2021

Streptomyces uses geosmin to ring the dinner bell for hungry springtails, which eat the bacteria, and in return the arthropods spread the bacteria’s spores far and wide. —Alex Fox, Smithsonian Magazine, 17 Apr. 2020

Word History

Etymology

Greek gē-, geō-, combining form of gê "earth" + osmḗ "odor" + -in entry 1 — more at geo-, anosmia

Note: Term introduced by the American biochemist Nancy N. Gerber (1929-85) and the French-born American biologist Hubert A. Lechevalier (1926-2015) in "Geosmin, an Earthy-Smelling Substance Isolated from Actinomycetes," Applied Microbiology, vol. 13, no. 6 (November, 1965), pp. 935-38.

First Known Use

1965, in the meaning defined above