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The Worst Coffee Habit You Need to Quit Right Now

This seemingly innocuous habit has some not-so-healthy repercussions.
leftover coffee from french press

It's something that perhaps we don't want to admit doing: drinking leftover coffee. When energy is in such short supply these days, you'll do whatever it takes to get that boost of motivation or focus—even if it means sipping on a cup of joe that was left on your desk for most of the day, or worse, overnight.

It's not just losing that valuable caffeine that will cause a pause before pouring out the pot. If you've ever put in the effort to make a French press or pour-over, you know it's like feeling your hard work being washed down the drain. But it's the right thing to do.

While you may think to yourself, "it's probably safe to drink leftover coffee since it's basically just water, right?" Well, the answer is more nuanced than you think.

We turned to the coffee and food safety experts to learn what we should know about drinking leftover coffee and why they recommend stopping the habit. (For more on how to keep your health in mind during your morning java, make sure to check out the Ugly Side Effects of Drinking Too Much Coffee, According to Science.)

Is it unsafe to drink leftover coffee?

If you just took a sip of coffee that has been sitting on your desk for a few hours, you don't have to worry too much.

"From a microbial standpoint, leftover coffee is relatively safe to drink," says Bryan Quoc Le, PhD, a food scientist and author of 150 Food Science Questions Answered. "Black coffee is a relatively poor medium for microbial growth since there are no readily-available nutrients such as sugar or protein," says Dr. Le.

However, coffee can start to accumulate minor amounts of mold or mold byproducts, which Dr. Le says could affect a small number of individuals with an allergic sensitivity to mold.

It's when you leave coffee in a pot for a day (or two…) when you may want to reconsider pouring yourself a cup. Dr. Le notes that "it takes a few days for coffee to grow mold."

Of course, if your coffee has milk in it, the maximum amount of time you should leave it out is two hours, according to food safety guidelines by the CDC. (Related: 7 Things You Should Never Add to Your Coffee.)

What about the taste?

The reason why most experts recommend ditching your leftover coffee habit is due to taste.

"The largest problem with leftover coffee is the flavor. The flavor molecules, aromatics, and oils in coffee are prone to oxidation, where oxygen in the air reacts with these compounds and form rancid byproducts that affect the flavor," says Dr. Le. He explains that one of the key aromas in coffee is highly susceptible to oxidation, and once this molecule is oxidized, coffee quickly loses its aroma and taste.

"I would not recommend drinking a day-old coffee simply because of its taste. Even if you keep it in the fridge, your coffee will lose its flavor and will become stale," adds Yurii Brown, Certified Barista and Founder of CoffeeGeekLab.com.

"It might also absorb the odors from your kitchen or the food inside the fridge. As a result, you will get a cup of god knows what, tasting like burnt water and smelling like the inside of your fridge," he adds.

One last thing to consider about leftover coffee is that some of the health benefits of the brew won't be as potent if it's left exposed to air. "Ingredients such as antioxidants can degrade over time, which can protect against aging and many diseases caused in part by oxidative stress," says Julien Raby, Founder & Owner of Coffee-Works.

What's the best way to store leftover coffee?

So now that we know leaving coffee on the counter isn't the ideal way to keep your cup, what should you be doing?

"If you intend to drink your coffee a day or more after it was brewed it is best to remove it from the pot quickly and place it under refrigeration," says Trista Best, MPH, RD, LD, a Registered Dietitian at Balance One Supplements.  "This will allow the halt of any bacterial growth and allow you to have an iced coffee in place of a traditional hot coffee."

"If you keep brewed coffee in the refrigerator then it should be good to go for 3-4 days," says Raby. "If you've kept it outside under room temperature, then try finishing it within 12-24 hours. If you're not able to do so, then dump it afterward because it isn't drinkable anymore," he adds.

Or, even better for you coffee lovers, don't have any leftover coffee to begin with!

"My best advice is to not brew so much coffee. Do not brew your coffee overnight—start the process while you get ready," says Sean Brennan, CMO & Coffee Scientist at Coffee Channel. For a better brew, "keep your coffee in airtight containers, bean or ground. To note, ground coffee oxidizes at a faster rate so don't ground too much at once, and if you do, store it properly," Brennan adds.

Ditch your habit of drinking old coffee, and for more ways to ensure you're drinking the best brew you can, don't miss these 11 Coffee Pot Mistakes You're Making.

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Olivia Tarantino
Olivia Tarantino is a senior editor of Eat This, Not That!, specializing in nutrition, health, and food product coverage. Read more
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