Researchers sampled 10 espresso machines and found that most of them harbored coffee residues rich in bacteria—including some potentially pathogenic strains. Christopher Intagliata reports
What's the liveliest part of your kitchen, in terms of harboring bacteria? Is it the cutting board? The dish sponge? Or maybe… your coffeemaker? Because even though caffeine has antibacterial effects, it turns out espresso machines can harbor a whole menagerie of bacteria—including some pathogenic species more commonly associated with the toilet.
Researchers sampled ten Nespresso brand espresso machines, [nespresso brew sound], zeroing in on the drip trays, which catch those last drops of brown gold after a brew. They found that nine of the ten machines harbored residues rich in Enterococcus bacteria, a typical marker of human fecal contamination. And another common resident was Pseudomonas—which has both benign and pathogenic strains. Pseudomonas appears to thrive in the presence of caffeine, and break it down. Which suggests the bugs might be put to work decaffeinating coffee, or cleaning caffeine residues from our waterways. The findings appear in the journal Scientific Reports. [Cristina Vilanova, Alba Iglesias & Manuel Porcar, The coffee-machine bacteriome: biodiversity and colonisation of the wasted coffee tray leach]
As for your next espresso shot? Don't worry too much. The researchers did not find any bacteria in the coffee pods themselves—so they say our fingertips might be to blame for spreading the single-celled invaders. And they write that it's "absolutely not the case" that Nespresso machines are dangerous for human health. Just wash the drip tray regularly with soap and water, as you would any other food-contaminated surface. So that the only thing brewing in your espresso machine… is your coffee.
[The above text is a transcript of this podcast.]
[Scientific American is part of Nature Publishing Group.]