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Naturally occurring alcohol with a distinct earthy-musty smell and taste. It is perceived as a typical soil odour, causes, among other things, the smell of mould fungi and occurs when rain starts after prolonged drought or in freshly ploughed soils. Geosmin is produced by microorganisms of certain bacteria (Myxobacteria and Streptomyces species) that mainly live in the soil (in the picture, fruiting bodies of Myxobacteria). Geosmin is also responsible for the typical smell of red beet. In wine, a weak earthy tone is to be understood as positive and is often the characteristic of certain French red wines (see under Stinky). When more pronounced, it indicates wine faults such as geranium, cork taint or horse sweat. The human sense of smell is highly sensitive to geosmin; the perception threshold is the incredibly small amount of 0.1 ppb (part per billion).

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Dominik Trick
Technischer Lehrer, staatl. geprüfter Sommelier, Hotelfachschule Heidelberg

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