Your coffee machine is a breeding ground for opportunistic microbes

November 26, 2015 – Anna Mehler Paperny, Global News

When did you last clean out your coffee machine? We mean the whole thing — including that tray at the bottom that catches all your spills.

Yeah, that’s what we thought.

Caffeine, that magical alkaloid compound, is not only an energy booster: It’s also a known antibacterial compound.

So you’d think a machine that makes caffeine-rich coffee would be bacteria-free.


Researchers from Spain’s Universitat de València studied the coffee waste reservoir (the pan at the bottom that catches spilled bits — “coffee lyxiviate,” if you want to get fancy) of 10 different Nespresso machines, chosen for their uniformity.

This is not a sterile environment. Far from it.

When the researchers sequenced the genetic material they found in the coffee machines they discovered a thriving community of diverse, “opportunistic,” caffeine-resistant bacteria that didn’t mind the hostile environment — a “highly variable microbiome rich in coffee-adapted bacteria.”

This held true regardless what machine model they tested or how many people were using it, researchers wrote. In some cases they found as many as 65 different genera, or organism subdivisions.

(There’s no indication these findings are specific to Nespresso machines. Global News contacted Nespresso for comment on the study anyway. We’ll post their reply when we hear back.)

One thing the researchers did find: The longer a machine was used, the more stable its microbial communities became.

So the cycles of hot liquids and caffeine accumulation help determine “the composition of the microbial community,” they write.

The researchers call this the first-ever attempt to colonize and systemically analyze bacteria in coffee machines. Without commenting on anyone’s dishwashing habits, we cannot corroborate this claim.

“Our results show, for the first time, that coffee leach from standard capsule machines is a rich substrate for bacterial growth; that caffeine content does not prevent a rich bacterial biodiversity from rapidly colonising coffee leach; and that microbial succession from an initial pool of generalist bacteria gives way to an apparently coffee-adapted but still highly variable bacteriome,” the study reads.

This could actually be a good thing: Caffeine is one of the most common signs of human pollution. These microbes could help clean it up.

“Our results may shed light on the microbial arsenal of caffeine degraders with important implications for both medicine and biotechnology,” the researchers write.

“The resistant microbial communities we describe here … may represent a promising tool for biological coffee decaffeination processes and for environmental caffeine decontamination.”

That said, these bacteria aren’t harmless. The study’s findings suggest you probably want to clean your coffeemaker regularly. With soap. Avoiding cross-contamination between your coffee-drip pan and other parts of the machine.

“The presence of bacterial genera with pathogenic properties and the fast recovery of the communities after rinsing the capsule container, strongly suggest the need for frequent maintenance of the capsule container of these machines.”

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