Your Coffee Machine Is Breeding Bacteria

Steve Meddle/REX Shutterstock
What do you usually put in your coffee in the morning? Cream? Sugar? A shot of antibiotic cleaner?

Maybe we should start considering that last one. A new study released on Monday found that the leftover coffee caught in the drip tray of a coffee machine — specifically the high-end Nespresso machine — is a great breeding ground for a certain kind of bacteria. The study, published in the open-access scientific journal Scientific Reports, found between 35 and 67 different types of bacteria hanging out in the waste trays of nine Nespresso machines that had been used for at least one year. Gross.

But importantly, the researchers discovered that most of the strains of bacteria could not only tolerate the high-levels of caffeine, but that, much like your frighteningly twitchy college roommate, they actually loved it.

The caffeine present in coffee is a natural alkaloid, which makes liquid coffee an inhospitable environment for bacteria. While people love the effects of caffeine, our bacterial neighbors can’t stand it. So it surprised the researchers to find that the strains of bacteria present had adapted to not only be able to live in what should have been a toxic environment, that they were thriving, breaking down the caffeine in a process called degradation and leaving behind no chemical residue. The same study also looked at a brand-new machine and found that the biodiversity evolved quickly, with caffeine-loving strains of bacteria replacing ones less tolerant to the chemical over the course of a few months.

Although you may suspect that this study was a not-so-subtle way of justifying all the coffee the researchers were drinking (“What do you mean you have nine Nespresso machines?”), there’s actually a very real need for this kind of research. While medicines like antibiotics and hormonal drugs get a lot of the attention in terms of wastewater pollution, caffeine is also a big polluter and can potentially be used to determine whether wastewater (what goes down your sink drain and flushes your toilet) has been properly treated. By figuring out which bacteria like caffeine, researchers are able to pinpoint which microbes are able to break down the chemical, leading to not only easier decaffeination of everybody’s favorite bean, but also newer and better treatments for polluted groundwater.

That’s definitely a cause worth looking into, and bacteria worth having around. Still, we think we’re going to go home and boil our coffeemaker trays. Twice. Just in case.
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