Your daily cup of coffee could be providing you with more than just an energy boost. A 2015 survey published in Scientific Reports tested the coffee machines of 10 different families and found that every single one contained some sort of bacterium. Bacteria strains discovered included staphylococcus, streptococcus, and E. coli. These germs could potentially cause gastrointestinal issues.
How to clean:
Your coffee maker should be cleaned once a month, following the
manufacturer’s instructions. The NSF recommends adding up to four cups
of undiluted vinegar to the reservoir, letting it stand for 30 minutes,
and then running the vinegar through the unit. To remove the vinegar
odor, run the machine with fresh water for two to three cycles.