Think your coffee maker cleans itself? There’s probably bacteria in there

DeLonghi Nespresso Lattissima
Bill Roberson/Digital Trends

When’s the last time you cleaned your coffee maker? If the answer is, “Uhhh …” you could have millions of little friends hanging out in the drip tray, according to a recent survey in Scientific Reports.

Microbiologists at the University of Valencia in Spain took samples from the drip trays of nine Nespresso machines, which use capsules similar to Keurigs. Between 35 and 67 different bacteria genera were basking in the trays’ leftover coffee.

That’s genera, not species — and if you remember from biology class that King Phillip Came Over From Great Spain (if you don’t, that’s the mnemonic for the order of taxonomy: Kingdom, Phylum, Class, Order, Family, Genus, Species) — genera (the plural of genus) come before species, and there were several different kinds of species in many of the genera. Sickness-causing pathogenic strains were also present.

Bacteria were found regardless of how often users brewed coffee or what type they made. While a CBS investigation earlier this year discovered one-cup makers had staphylococcus, streptococcus, bacillus cereus, and e-coli, it’s not just these capsule models that likely have bacteria. In fact, coffee mugs are contaminated, too. “In our studies, half had fecal bacteria in them,” microbiologist Dr. Charles Gerba told Fox News in 2013. “People probably contaminate them when they wipe them out with sponges or cleaning cloths.” (Yeah, your sponge is probably filthy.)

Luckily, there’s a fairly easy fix. Washing your machine every week with warm water, soap and maybe a tiny amount of bleach would “decrease bacterial densities to very low values,” study author Manuel Porcar told Quartz. While you may think your coffee maker gets hot enough to self-clean, water actually needs to reach boiling to kill those germs, says Donna Duberg, an assistant professor of clinical laboratory science at Saint Louis University.

Running the parts through the dishwasher on the sanitize cycle is a good start, but Duberg tells Fox you should still run one part water and one part vinegar through the machine monthly. “Vinegar is five-percent acetic acid and actually disinfects the coffee maker, killing almost 100 percent of bacteria and viruses and most of the fuzzy molds,” Duberg says. Interrupt the cycle halfway through, leave it for an hour, then start it up again. Repeat, then follow with two cycles of clean water. And throw out that sponge, or zap it in the microwave.