Is It OK To Drink Day Old Coffee?

What happens if you leave your cup of coffee out until the next morning? Is it OK to drink day old coffee? Why or why not? Let's find out the reason why.

Is It OK To Drink Day Old Coffee - holding a cup of coffee beside a laptop
A day old coffee experience more oxidation

Picture this scene: a pot of coffee sits on a breakroom or gas station counter, perhaps with the light still on the machine. You pick up the pot and notice that it's warm but not hot. Since you're so exhausted, you decide to pour a cup. After raising it to your lips, you notice the coffee is bitter and unpleasant. 

Congratulations, you just drank day-old coffee. 

Most of us have been in this situation before and wondered, is it OK to drink day-old coffee? Technically speaking, yes, it is. However, there is some dispute about the definition of “OK.”

Day-old coffee won't be teeming with harmful bacteria like some other beverages, but it certainly pales compared to a fresh pot. So, with that in mind, let's take a closer look at what happens with coffee when it sits out and what you can do about it. 

The Science Of Coffee Oxidation

All foods oxidize as they sit out in the open. Oxidation is part of what causes food to rot (along with bacteria). Some products, like coffee, take a long time to oxidize to the point where you'll get sick from ingesting them.

However, oxidation doesn't just make coffee expire; it also changes its flavor profile. It's important to note that oxidation also happens during the roasting and brewing process. The longer the beans are heated, the more they oxidize.

Over time, the natural compounds in coffee will break down, leading to a more acidic and bitter-tasting beverage. So, day-old coffee will experience much more oxidation than a fresh batch.

One way to mitigate this process is to store the liquid in the refrigerator, where it's exposed to less oxygen and other environmental elements. That said, if you try to reheat cold coffee, you'll degrade it much faster, leading to an even worse-tasting brew. 

Does Coffee Need To Be Refrigerated Once Brewed? 

open refrigerator with lots of food and drinks
Don't put your coffee inside a refrigerator immediately after brewing

Technically, no. While bacteria and mold can grow in brewed coffee, it takes a few days before they reach harmful levels. For example, if you leave a pot sitting in a coffee maker for a week, you'll notice spots of mold growing on the surface. 

Overall, coffee can be left out for several hours or a couple of days, provided that it hasn't been mixed with anything. Once you add other ingredients like milk and sugar, those elements will break down and grow harmful bacteria much faster. 

The Best Ways To Drink Day Old Coffee

Ideally, you won't have to drink day-old coffee too often, but if you find yourself in this position, there are a few ways to mitigate any sour flavors or bitterness. 

While it may be tempting to re-heat your coffee in the microwave, doing so will only oxidate the beverage faster, leading to a more bitter and burnt taste. If you're going to microwave coffee, it should be relatively fresh (within a couple of hours if possible). 

The Final Word: Is It OK To Drink Day Old Coffee?

Overall, drinking day-old coffee should be a last resort (unless you're talking about cold brew varieties). Just because you can drink it and not get sick doesn't mean you should. There are other ways to get your caffeine fix, so don't assume that it's day-old coffee or nothing. 

That said, individuals who like their coffee a bit more acidic and bitter may not mind a day-old beverage. Older generations would often brew a whole pot at the beginning of the week and drink from it for a few days before replenishing it with new coffee. To each their own. 

Day Old Coffee FAQs

Does coffee go bad overnight?

If by “going bad” you mean that it will be harmful to drink, no, it doesn't. If coffee sits out overnight, it will be much more bitter in the morning than if you refrigerated it, but it won't make you sick. 

Does all coffee taste bitter after sitting out?

Yes, all coffee will become more bitter after sitting out for a while. Since lighter roasts are already relatively bitter, the difference might be less noticeable than day-old dark roast coffee.

Author

  • Jonathan is an avid coffee drinker, although he's known to knock back a few energy drinks too. He's been a writer for over seven years, which is why caffeine runs through his veins.