Is It Gross to Keep Drinking the Same Cup of Coffee Throughout the Day? A Food Safety Expert Weighs In

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There are two types of coffee drinkers: People who are halfway done their with large cold brew before they've even left the Starbucks parking lot, and those who prefer to nurse their coffee as slowly as possible, often for hours on end.

Or maybe you're the type of coffee drinker who pours a morning cup that you so desperately desire, but the needs of the universe tug at your arm and you're unable to enjoy it. Kids need help getting dressed for school. The dog needs to be walked. When you finally spot your now cold coffee on your dresser, you shrug and pop it in the microwave for 30 seconds before taking a sip.

Experts In This Article

While you certainly wouldn't consume a beverage that had been sitting out for hours at a restaurant, home works a little differently; these rules don't always apply. If you're shifting uncomfortably in your seat remembering the multiple times you've sipped a soy latte in the afternoon that you bought before breakfast, you're certainly not alone. We all do this far more frequently than we'd like to assume, and every time we've lived to tell the tale. But cards on the table, we're here to face the question head-on: Just how gross is it to keep drinking the same cup of coffee throughout the day (or reheating an hours-old cup)? Is there any actual harm in drinking coffee left out? Read on for the food safety expert's input.

Is having coffee every day healthy? Here's what a registered dietitian thinks:

Is it safe to sip the same coffee for hours at a time?

According to food safety expert Jeff Nelken, this depends on a few factors, including what you're putting in your coffee when you make it. "Bacteria in room temperature liquid doubles every 20 minutes," Nelken says. This, he says, is especially important intel if someone is adding milk to their coffee. Drinking spoiled milk can lead to food poisoning—definitely not what you want from your cup of coffee. This is why milk shouldn't sit out for more than two hours.

Bacteria can start growing in coffee that doesn't have dairy milk in it too. This includes coffee that's straight-up black or spiked with an alternative milk or alt-creamer. But the reason why coffee with dairy milk in it is more concerning is because of its composition; the milk starts to spoil. The chemical composition of coffee also changes the longer it sits out, but Nelken says that it's still safe to consume black coffee or coffee with vegan milk in it if it's been sitting out for hours—it just may not taste great. He also says reheating your coffee in the microwave isn't a big deal.

If you still want to lean on the side of safety—and don't want to have to reheat your coffee in the microwave throughout the morning—pour your brew into a temperature-controlled mug that keeps it at a safe temperature that prevents bacteria from forming while you slowly sip it.

smart mug warmer
Photo: Vsitoo
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Control the temperature of your mug by using the touch button or via an app on your phone.

The good news is that, in general, Nelken says drinking coffee left out is actually pretty safe. However, if you like to add dairy milk or cream to your cappucino or cold brew, it's better to dump it after two hours. Hey, it's just another reason it's worth stocking your fridge with oat milk instead.

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