You walk over to the office coffee pot and have a sad realization. No one has made a fresh pot for at least eight hours. Judging by the pot’s lukewarm temperature, you’re going to have to heat your cup of joe in the microwave. No coffee lover would look forward to the bland taste—but is day-old coffee safe to drink?
Is Day-Old Coffee Safe to Drink?
The short answer: probably. If the coffee already has milk or creamer in it, you shouldn’t drink it if it’s been sitting out unrefrigerated for too long.
But while day-old coffee likely won’t put your health in jeopardy, but there are still some good reasons to get your cup of caffeination piping hot. Your coffee machine isn’t exactly clean, according to Donna Duberg, MA, MS, an assistant professor of clinical laboratory science at Saint Louis University.
“Germs are present in every corner of our lives,” Duberg told Fox News. “Are there germs in our coffee makers? Yes. Will they make us sick? Maybe, if there are enough of them, and especially if we don’t clean our pots often enough.”
You might want to finish your lunch before reading Duberg’s next assertion. “Bacteria forms a slick biofilm when grown in moist, dark places, and so do molds.” She went on to say, “If there is obvious slimy stuff in the coffee maker … this is a good sign there is something growing.” Yeah, that’s not exactly appetizing.
Isn’t Coffee Antibacterial?
“While coffee brewed from roasted beans does have some antibacterial action due to its acidity, there is research which shows that it is only about 50 percent effective in killing bacteria, such as Staphylococcus aureus and Streptococcus mutans, and molds,” Duberg said.
In other words, your coffee isn’t going to fight germs on its own. The coffee filter doesn’t help, either, as it only filters out chemicals and metals—not living microorganisms.
But wait. Coffee gets really hot, right? Yes, but your coffee maker doesn’t sterilize itself during each brew cycle. Water needs to boil for about a minute to kill off all the potentially hazardous germs that could be lurking within.
Why Does Day-Old Coffee Taste Bad?
Interestingly, the presence of molds and bacteria aren’t the reason day-old coffee tastes so bad. As the coffee sits, its chemical composition changes, breaking down the delicate compounds that give the drink its sought-after taste. If you leave the burner on, that further alters the taste by—shocker—burning the coffee.
Ultimately, old coffee probably isn’t dangerous, despite not tasting as good as a freshly brewed cup.
How Should I Clean My Coffee Pot?
Day-old coffee is safe to drink, provided that you clean your coffee pot on a regular basis.
To do so, run a solution of equal parts vinegar and water through the machine at least once a month (perhaps slightly more often in offices, where coffee machines are more heavily used). After running the vinegar water mixture through the machine, run a cycle with pure water to get rid of any leftover vinegar that might sour your next brew.
That process should help to get rid of any potentially dangerous bacteria. The good news is that if you’re cleaning your coffee maker regularly, you probably don’t have to worry about drinking the occasional cup of day-old coffee—just don’t expect it to taste great.
Oh, and don’t forget to clean your mug. Thoroughly. “Coffee mugs are usually [the] worst,” microbiologist Dr. Charles Gerba told Fox. “In our studies, half had fecal bacteria in them. People probably contaminate them when they wipe them out with sponges or cleaning cloths.” On second thought, maybe we’ll just stock up on disposable cups.