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).

Peasy Beans

This defect, encountered only in Central African arabica coffees, is due to a contamination of the cherry by a bacterium of the entherobacteriaceae.

Rioy Beans

These beans have a flavor described as medicinal and iodine-like. Rio-tainted beans are heavily infested with moulds (Aspergilli, Fusaria, Penicillia, Rhizopus), and bacteria (Lactobacilli, Streptococci).

Sour Beans

Sour (ardido) beans are deteriorated by excess fermentation, with a sour taste.

Stinker Beans

Stinkers are over-fermented beans, usually with normal appearance but a rotten smell and flavour.

Whitish Beans

The surface discoloration of whitish beans is due to fermentation by Streptococcus bacteria.The attack can occur if storage is too long or in conditions of excessive humidity.

All of these sorts of beans should have been sorted out on the coffee plantation, avoided by proper storage or removed when discovered along the supply chain. But do good coffee beans go bad once you have purchased them?

Old and Perhaps Moldy Coffee Beans

Mold is always an issue when foodstuffs are stored in damp areas. Coffee beans, green or roasted or ground coffee should be stored in a cool and dry place. And coffee is best when made and consume in a timely manner. Green coffee beans properly stored are good for two years. Roasted coffee beans properly stored are OK for up to six months. Ground coffee where the inside of the bean is now exposed to the air started to get stale on the spot. You best bet to avoid bad beans is to purchase from a reliable supplier and store appropriately. Roast only what you are going to use that day and grin only what you are going to use to make the next batch of coffee.

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