Aroma geosmin

Cybullol (377), previously reported as a metabolite of Bird s Nest fungi (c/. Vol. 7, p. 95), and geosmin (379), a degradation product of cybullol and the fungal metabolite responsible for the earthy aroma of freshly ploughed soil, have been synthesized by the routes outlined in Schemes 36 and 37. ... 

Geosmin was previously found in red beets Beta vulgaris L.) by Murray et al. (1975) and Tyler et al. (1978) and is known as a contaminant of water supplies. A very low aroma threshold of 0.021 ppb is found by Buttery et al. (1976a). By GC-sniffing, Spadone et al. (1990) characterized it as an important contributor to the Rio off-odor, with its earthy-musty odor typical of freshly-ploughed soil. 

Besides trichloroanisole, other metabolites such as guaiacol, geosmin, 2-methylisoborneol, and 2-methoxy-3,5-dimethylpyrazine (Fig. 4.4) can also cause musty or moldy aromas (Silva Pereira et al., 2000 Simpson et al., 2004). Moreover, Silva Pereira et al. (2000) pointed out that cork taints can originate from other microorganisms. As an example, a putrid odor is produced by Armillaria mellea, a microorganism that infects oak trees and causes yellow spot on corks. 

The character-impact compound of green bell pepper, 2-isobutyl-3-methoxypyrazine, was the first example of a high-impact aroma compound because of its exceptionally low odor threshold of 2 parts-per-trillion (ppt) (15). It is also responsible for the vegetative aroma of Cabernet Sauvignon wine (23b). A similarly low odor threshold compound, geosmin, is the character impact... 

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