Smell That?

The return of the earthy scents is one of my favorite parts of the transition from winter back into spring.  Of all of the flavors, the scent of rain is the most unmistakable.

One of the primary contributors to this distincitive smell is the bicyclic organic compound shown here, geosmin.  According to Wikipedia, it is produced by a number of soil bacteria such as the Actinomycetes (which also have a variety of biotechnological uses), and is also responsible for the earthy taste of beets and bottom-dwelling freshwater fish.  The human nose can detect geosmin at vanishingly low parts-per-trillion concentrations.

Ahhh... the sweet smell of microbial metabolic biochemistry.