Geosminis an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather or when soil is disturbed. The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion. Geosmin is produced by several classes of microbes, including cyanobacteria (blue-green algae) and actinobacteria, and released when these microbes die. Communities whose water supply depends on surface water can periodically experience episodes of unpleasant-tasting water when a sharp drop in the population of these bacteria releases geosmin into the local water supply. Under acidic conditions, geosmin decomposes into odorless substances.
