coffee leaved to sit out

How Long Can Coffee Sit?

We’ve all been guilty of making ourselves a hot cup of coffee with the intention to sit down and enjoy it at its ideal temperature, but then letting life get in the way. It’s the disaster to be avoided by any serious coffee maker.

Whether you’ve got kids around or just a busy schedule, it’s common for your coffee to get cold and for you to just end up making a new one.

Some people don’t want to waste any amount of coffee, though, especially if it is a high-quality one. Instead, they try to heat leftover coffee rather than make a fresh one. 

However, the question stands: how long does coffee actually last when it sits out?

This depends entirely on the brewing method, as there are some styles of coffee that do better when left to sit awhile. For a standard cup of instant coffee though, you shouldn’t drink it after its 12 hours of shelf life, as there are health concerns involved if you do.

If you’re one of the offenders who regularly leave their coffee to sit out well past its ideal temperature, this is the guide for you. We’re going to explore how long can coffee sit out in every type of scenario, the potential effects, and how the flavor is altered, so you can determine whether or not it’s worth salvaging the next time you forget your cup of joe.

Different Brewing Times for Coffee

brewing time

Before we can jump into whether or not a coffee that’s been left out should be drunk, it’s good to note that there are lots of different styles of coffee, and each has its own guidelines.

The way the brewed coffee was made and is subsequently prepared to be served will impact its ability to be left out and enjoyed later or not, so check out some of these common brewing methods.

  • Instant coffee
    This method uses coffee grounds or expanded coffee beans diluted with hot water and stirred, without the need to filter. When making an instant coffee, you shouldn’t leave it out any longer than the day, and if it’s been mixed with milk you should only drink it while it’s still warm.
  • French press
    A French press is a traditional method for making coffee that features ground beans and hot water being left to steep, before plunging and filtering the beans and leaving the coffee to enjoy. Coffee made this way should be instantly poured from the carafe as it will keep brewing otherwise, leaving you with a very bitter cup.
  • Cold brew
    As the name suggests, cold brew coffee is brewed with cold or room temperature water. The process takes a minimum of 12 hours as the ground coffee is steeped with water and then filtered out. Generally, this type of coffee can stay out a little longer but should ideally be refrigerated.
  • Espresso
    An espresso machine brews coffee by filtering hot water through ground coffee beans. This method of brewing is best enjoyed while it’s still hot. It can, however, be drunk for that day only provided it hasn’t been mixed with milk, but will likely not taste as good.

The Chemistry of Coffee

One of the main reasons why you should avoid drinking coffee that’s been left out too long is the oxidation process.

While it’s completely safe to drink coffee that you made that morning when it’s cold in the afternoon, the taste will be different and it likely won’t have the same effect.

This occurs due to oxidation, which is the process of air (oxygen) being mixed with the roasted coffee beans. Oxygen has a corruptive effect on the structure of many substances, including coffee (whether already brewed or not).

You might not be able to see a difference, but oxidation is working on the flavor compounds of the coffee and deteriorating them. The result is a coffee that’s a lot less flavorsome, and probably lower in caffeine content as well. Such coffee can also be less healthy since the oxidized components change in their chemical structure—and not always for the better.

The oxidation process is also a problem with beans that haven’t been ground yet, which is why they need to be stored in an airtight container and used almost immediately after breaking the seal.

Can Coffee Lose Its Flavor?

coffee flavour

If left for too long, definitely. But you’ll notice this yourself anyway.

The best time to enjoy a coffee if you want its full flavor is immediately after you brewed it & while it’s still hot. 

As discussed earlier with oxidization, as soon as the hot water has hit the ground coffee and released its acids, oils, and aromas, it will be at its most potent and flavorsome, so it’s the best time to enjoy.

You might have noticed if you ever drank a cup of stale coffee that sat out that it had lost some flavor, and even after heating it in the microwave, it fails to pack the same punch as before. This is completely normal due to oxidation which corrupts the coffee beans’ optimal flavor, which is impossible to get back again.

Heat and the Bitterness of Coffee

The soluble substances in coffee work with specific temperatures to get the best effect and deliver us with the best-tasting coffee.

When dissolved between 195 to 205 degrees Fahrenheit (around 95-96 degrees Celsius), coffee will be most flavorsome and full-bodied, so this is the ideal time to enjoy it.

The oxidation process doesn’t just stop after this, as it continues to brew. The result is a bitter cup of coffee that has continued to have this reaction between hydrogen and oxygen, and now has a higher pH level than before. You’ll notice the coffee tastes more bitter and probably stale, even if you try to reheat it.

Cold brew coffee works on this same premise, but rather than reaching those higher temperatures to extract the aromas and oils quickly, it’s a slow process.

This slower brewing time means you’re left with a less bitter tasting cup of coffee, and also with a drink that will do a lot better in the fridge for up to a week, or even left out for a day after brewing, provided there have been no additives mixed with it. The best way to go about it, though, is to cover your cup with a piece of tissue—or simply close your carafe’s lid.

Making Your Coffee Last Longer

tips for longer coffee taste

If you’re a habitual forgetter of coffee, there are some things you can do to help yourself.

Follow these tips to make sure your coffee lasts longer and you get the most enjoyable aroma and all of the benefits that the drink has to offer.

  • Refrigerate your coffee
    As soon as your coffee has been brewed, put it in the fridge in an airtight bottle and store it for future use. Heat it before adding any milk or sweeteners to it. On the other hand, if unrefrigerated and kept at room temperature, it will last only for half a day or a whole day at best.
  • Use a thermos
    A thermos has been insulated to keep temperatures just as they are, which means you have hot coffee for hours. If you always leave it laying around to get cold, make the switch to a thermos so it’s good all morning. The thermos can also keep your iced coffee, well, iced for hours.
  • Make cold brew
    Cold brew coffee can be made in a big batch and stored in the fridge without relying on the heat for the oxidation process. When you want a glass, you simply pour over ice and enjoy.

Frequently Asked Questions

Although one might assume coffee is a drink that would be good for days, there are lots of problems with trying to drink an old cup. 

We’ve answered some more questions about the best way to enjoy your morning coffee to get the most out of it, so check out these FAQs.

Can You Get Sick From Old Coffee?

Although you probably won’t get ill from drinking black coffee that’s been left out, it surely won’t taste as good.

Unless there’s apparent mold in your coffee, it’s safe to drink, but it will be without most of its full-bodied flavor and the caffeine content that people use to get the stimulating effects this drink has.

Remember that oxidation has a corruptive effect on the chemical structure of coffee, and these changes are rarely for the better. No, it doesn’t mean you will get cancer from drinking a single forgotten cup—but it’s best, and far tastier, to brew fresh coffee anyway. Or just head on to the local café or Starbucks and ask for a fresh cup from the barista.

Does Ground Coffee Go Bad?

Yes, but it takes a really long time—in practice, far longer than you’d take to consume it.

If you brew your coffee with fresh ground or whole beans, there are rules to follow regarding when they should be used.

An unopened bag of pre-ground coffee is good for up to a year depending on when it was roasted, and if you leave it in the freezer during this time unopened, it can last up to two years. An opened bag will last for a month to three. You can always check the expiration date printed on the label.

Most of these bags have a sealing method so that they retain the freshness as long as possible—sometimes even months. 

How Long Should Cold Brew Steep For?

Cold brew is intended to be left for at least 12 hours for the brewing process to complete, and around 16 hours for the best results.

However, you should never leave it to brew for more than 18 hours otherwise the coffee will be bitter and rancid, with its flavor likely being unpleasant. The reason is that the more time you leave it work its magic the more it extracts the essence from the beans, including their bitterness.