Scientists have found that all kinds of pathogens gather in coffee grounds and in used pod machine capsules.
According to the German News Agency (DPA), Fritz Titgemeyer, head of the Food Microbiology Laboratory at the Munster University of Applied Sciences in Germany, said that damp coffee grounds encourage the growth of germs.
If you leave a used coffee pod in the machine for a few days before throwing it out, some mould spores may remain in there and you may be adding them to your next brew.
Titgemeyer noted that a heat-stable poison may have developed, a so-called mycotoxin, and you will not be able to see or taste it.
The water containers and the plastic tubes in coffee machines are also a perfect breeding ground for bacteria if they are not cleaned properly. The expert said that bacteria can settle there in the form of biofilms. All removable components need to be cleaned thoroughly.
Titgemeyer added however disgusting it may be to imagine one's coffee machine full of microorganisms, they do not really pose a health risk.
"The water is heated to 80 degrees Celsius, which kills any germs present in the water tank," he said.
If you use the machine to make cold drinks, however, you may need to worry. Titgemeyer explained that in cold-extracted drinks like iced tea or iced coffee, all germs will remain. The good news is that many coffee machines include a self-cleaning program, but there are also extra things you can do to make sure you keep the germs at bay.