http://buyorganiccoffee.org/1681/do-coffee-beans-go-bad/ Do Coffee Beans Go Bad? If you buy coffee beans, green or roasted, to make coffee at home you don’t want them to go bad. Do coffee beans go bad? There are two issues with bad coffee beans. One is poorly sorted beans after picking and the other is improper storage in transit or in your home. Stinkers and Other Beans Gone Bad There is an excellent article at TCC about defected beans. There are black beans and earthy beans, moldy beans and peasy beans. You want to avoid rioy beans, sour beans, stinker beans and whitish beans as well. Black Beans Black beans, where the interior of the bean is also more or less completely black depending on the severity of the attack, are beans having undergone a yeast fermentation starting at the epidermis; the surface of the bean is covered with minute holes surrounded by mineral micro crystals, left after enzymatic degradation of cellulose. The more serious the damage, the blacker is the interior of the bean. Earthy Beans The presence of 2-methylisoborneol, a secondary metabolite of Actinomycetes, Cyanobacteria and molds, has been associated with the earthy flavor of robusta coffee. The levels present in robusta coffee are at least three times as high as in arabica (Vitzthum et al., 1990). These data indicate that robusta taste results, at least partially, from contamination by microorganisms rather than from specific aroma components. Moldy Beans A mould/yeast level above 105/g is always associated with mustiness in flavor. Geosmin, identified in a heavily rioy and musty tasting sample of Portorican coffee, is probably the substance responsible for moldiness in beans (Spadone et al., 1990).