How Long Can Coffee Sit Out? Here's the Truth

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I don’t know about you, but I can’t make it through the day without coffee. My morning coffee really gets things going, but that afternoon lull often requires a caffeine top up.

One of my go-to brew methods is a French press, and I’ll admit I’m guilty of reheating what’s left of the morning’s coffee some days. I know the better move is to brew a fresh pot of coffee, or turn to my trusty AeroPress, but what’s the harm in drinking hours-old coffee? How long is too long for my coffee to sit out?

For optimal freshness, you want to drink your coffee within 30 minutes of brewing. If you drink black coffee, it’s going to take a very long time before your coffee becomes unsafe to drink, but as soon as you start making additions to your cup of coffee, things get a bit murkier.

Let’s break down the specifics of coffee freshness and safety, so you can get the best out of every cup and ensure you’re not wading into dangerously muddy waters.

How Long Can Coffee Sit Out?

How long your coffee can sit out depends on how you make it. For example, black coffee is still safe to drink after 24 hours, but coffee with dairy should be tossed out after just two hours.

Let’s break down the freshness and safety windows in detail….

Fresh Is Best

Most coffee experts agree that if you want the best version of your coffee, you should drink it within 30 minutes of brewing. At the 30-minute mark the flavors and aromas start to dissipate and degrade, and after about four hours you’ll start to notice some harsh bitterness creeping in. The main reason for this flavor degradation is the process of oxidization, the aromatic compounds in your coffee coming into contact with oxygen.

From the point of brewing, your coffee undergoes a series of chemical reactions that release oils and aromatics. These extremely volatile solubles are what give your coffee its unique and complex flavor profile, but as soon as they are exposed to oxygen they begin to degrade and evaporate. The chemical reaction that occurs when oxygen mixes with the hydrogen in your coffee raises its pH, which is why you taste an increased bitterness the longer your coffee sits out.

Higher temperatures accelerate the oxidization process, so reheating your coffee only leads to further degradation of both flavor and aroma. Rather than reheating your stale coffee, try an insulated travel mug or thermos to keep the coffee hot. We love the Zojirushi Stainless Steel Mug and the Yeti Rambler. If drinking out of a travel tumbler isn’t your jam, you can always use it for storage and transfer into your favorite mug when ready.

If you really don’t want to waste leftover coffee, store it in an airtight container in the fridge. This will arrest the oxidation process somewhat and is the best bet for retaining those aromatics. Rather than reheating this coffee the next day, I like to add a little dairy and sweetener and shake that up into a tasty iced coffee treat. It’s a bit of a cheat, I know, as those additions mask any harsh flavors, but it’s still delicious and a great way to avoid coffee wastage.

To recap: consuming hot coffee within 30 minutes is the best way to enjoy it, and if we want to save leftover coffee, an airtight container is essential. But at what point does our coffee actually become unsafe to drink?

How Long Can Coffee Sit Out Before It’s Unsafe To Drink?

Black Coffee

If you like your coffee black, the good news is you can leave black coffee out for days before it will become unsafe to drink. It won’t taste very good, but it won’t be harmful.

Coffee lacks proteins and carbohydrates for microorganisms to feed on, so plain black coffee isn’t much of a breeding ground for bacteria. Mold will appear eventually, but that will take at least 4-7 days, if not longer. It’s generally recommended that even black coffee not be left at room temperature for more than 24 hours, just to be safe.

Remember it’s best to store leftover coffee in an airtight container in the fridge.

Coffee with Milk Added

If you add dairy to your coffee, or prefer a frothy latte or cappuccino, things get dicey much quicker. You should consume coffee with the addition of dairy or a dairy alternative within 1-2 hours of preparation. After this point, toss it. When milk and other perishables sit within a temperature range of 40-140 degrees Fahrenheit (4.4-60 degrees Celsius), bacteria will grow rather quickly and the coffee will become unsafe to consume after about two hours.

As with black coffee, the coffee flavor and aromas will deteriorate within the first 30 minutes. If you typically consume milk-based coffee beverages, particularly with sweetener, you might not notice the degradation of flavor quite as much, but we all know a lukewarm latte is not all that enjoyable. If you notice a sour coffee taste, it’s definitely time to toss your beverage.

If you tend to drink slowly, opt for an insulated thermos or tumbler to keep your drink at a safe temperature.

Never put leftover coffee with dairy into the fridge if it’s been sitting out, and avoid reheating milk-based beverages. Reheating might kill some bacteria, but it’s not worth the risk and the drink will taste pretty terrible.

Cold Brew Coffee

Cold brew coffee lasts the longest. It stays fresher longer since heat accelerates oxidation, and you can keep it in an airtight container in the fridge for up to two weeks.

The best method is to make a straight cold brew concentrate, adding water and any other fixings to it per serving.

Cold brew is delicious, retaining more flavor and aromas than any other method, and it’s not just for the summer. Enjoy cold brew anytime of the year, particularly when you’re rushed in the morning. Cold brew requires a bit more time upfront, but once it’s brewed simply grab it out of the fridge and you’re ready to roll.

Clean Caffeine

One thing you don’t need to worry about is your brewed coffee losing its caffeine content. Caffeine is quite stable and doesn’t degrade like flavor and aroma do. However, the antioxidants in fresh coffee do dissipate, so drinking leftover coffee isn’t as good as a fresh cup of coffee. It might be worth dumping that day-old coffee after all.

Speaking of coffee pots—you definitely want to keep yours clean. Although coffee itself isn’t particularly attractive for bacteria, your coffee machine can be and there’s a rather pernicious strain—called Pseudomonas putida—that degrades caffeine.

How to best clean your coffee maker really depends on what brew method you use, so check your user manual and give your coffee maker and coffee pot a deep clean from time to time to ensure you’re brewing the best-tasting coffee possible.

Summary

Morning coffee should be enjoyed within 30 minutes.
Black coffee will stay fairly fresh for about four hours after brewing, but it’s still safe to drink 24 hours later and can be kept in an airtight container in the fridge for up to a week.
Cold brew is a great way to enjoy fresh coffee with virtually no waste.
Coffee with dairy should be tossed after two hours.