Black coffee is a popular morning ritual for many people. The convenience of brewing a fresh pot and enjoying it immediately is ideal. But life often gets in the way, leading to full mugs forgotten and left to cool. So, is it safe to drink that forgotten black coffee that’s been sitting out?
Quick Answer
Yes, it is generally safe to drink black coffee that has been sitting out, as long as it has not been sitting for several hours. Black coffee that has been left at room temperature for more than 2 hours may start to become unpalatable or unsafe to drink.
How Long Can Black Coffee Sit Out?
Freshly brewed black coffee is best consumed immediately, when it is piping hot. However, black coffee can be left out at room temperature for a couple of hours before it starts to suffer any negative effects.
Here is a quick overview of how long black coffee can sit before becoming less than ideal to drink:
30 Minutes – 1 Hour
Coffee that has been sitting out for 30 minutes up to an hour is generally fine to drink. At this point, the coffee will be cooler and less aromatic than fresh hot coffee, but still pleasant to drink for most people. No significant harmful bacterial growth will occur in this timeframe.
1 – 2 Hours
After sitting for 1-2 hours, coffee may start to taste more bitter and unpalatable. This is due to the coffee continuing to oxidize and release CO2. While bacterial growth is still minimal and likely safe, the taste decline means coffee is best consumed within about an hour of brewing.
2 – 4 Hours
In the 2-4 hour window, black coffee left sitting out starts to become questionable in terms of safety and taste. Bacterial growth may start accelerating, causing off-flavors. Oils in the coffee may go rancid. The coffee will likely taste flat and bitter. Most people will not enjoy coffee that has been left out this long.
4+ Hours
After 4 hours, do not drink the coffee. At this point, harmful bacteria like Bacillus cereus and Staphylococcus aureus may have multiplied to dangerous levels. The coffee will not taste good. Stale, bitter, and potentially unsafe coffee should be discarded at this point.
So in summary, drink coffee within an hour or two for best taste and safety. After more than 4 hours, throw out the coffee instead of drinking it.
Factors That Affect How Long Coffee Can Sit Out
Not all coffee that has been sitting out follows this exact 1-4 hour timeline. Certain factors can affect how soon the coffee becomes unpalatable or potentially dangerous:
Temperature
The hotter the coffee when initially brewed and poured, the longer it will retain heat and remain safe at room temperature. Coffee that starts out at 180-200°F may stay satisfactory for up to 2 hours. Coffee that starts out at 140°F may deteriorate more rapidly.
Processing Method
The way the coffee beans were processed and roasted affects the coffee’s stability. Lighter roasts tend to deteriorate faster, while darker French roasts are more shelf-stable and can be left sitting out a bit longer.
Added Ingredients
Added dairy, sugar, flavors etc. cause coffee to go bad more quickly compared to plain black coffee. Milk provides nutrients that bacteria can feed on. Sugar can ferment. Avoid leaving out doctored coffee.
Container Material
Coffee left in an insulated metal carafe or stainless steel tumbler may retain heat longer and stay fresher than coffee left sitting in a ceramic mug. The container affects cooling speed.
Environment
Temperature, humidity levels, and other environmental factors also impact how long coffee can safely or pleasantly sit out. Hot & humid environments speed up deterioration.
So coffee sitting in a hot kitchen for 2 hours may be less drinkable than coffee sitting for 2 hours in an air-conditioned room.
How to Tell if Coffee Has Gone Bad
Aside from the guideline timeframes above, you can judge whether old coffee is still good in a few ways:
Smell
Fresh coffee has an inviting, rich aroma. As it goes stale, the smell becomes harsh and unpleasant. Bad coffee gives off a sour, acrid odor. If your coffee smells off, it’s a sign it has spoiled.
Taste
Stale coffee will simply taste off – rancid, bitter, sour, or flat. It may even offer an unpleasant mouthfeel. A small sip will confirm if your old coffee is still palatable or should be discarded.
Appearance
As coffee oxidizes and goes bad, the hue darkens. Mold growth may occur. Watch for blackening, a whitish film, green dots, or cloudy accumulation at the top of old coffee.
Texture
Freshly brewed coffee has a smooth, silky mouthfeel. Old coffee develops a gritty, granular texture, which is another red flag.
Can Mold Grow in Coffee?
Yes, mold can grow in coffee, if it is left sitting out too long.
Coffee provides a hospitable environment for mold thanks to its warmth, nutrients, and moisture. Leaving coffee sitting out allows mold spores floating in the air to land in the coffee and multiply.
Common molds that can grow in old coffee include:
Aspergillus
This fungus appears as tiny black dots that form clustered colonies in old coffee. It gives off a foul, musty odor.
Penicillium
Known for blue and green hues, this mold creates a velvety film on the surface of stale coffee. It imparts a rotten smell.
Mucor
With a blackish, hairy appearance, mucor mold grows rapidly in room temperature coffee after several hours.
In general, mold takes about 4 hours to start visibly growing in coffee. So if you see obvious mold growth in your old coffee, you should certainly not drink it. Discard moldy coffee.
Can Bacteria Grow in Coffee?
Yes, bacteria can grow in coffee that sits out too long. The warm, nutrient-rich environment of brewed coffee makes an ideal breeding ground for bacteria.
Some types of bacteria that may proliferate in old coffee include:
Bacillus cereus
This is a spore-forming bacteria that thrives on starchy foods like coffee. It can cause vomiting and diarrhea if ingested.
Staphylococcus aureus
S. aureus releases toxins as it multiplies, which can lead to severe gastrointestinal illness.
Escherichia coli (E. coli)
Potentially present if coffee making equipment is contaminated, E. coli also causes intestinal illness when ingested.
Salmonella
Rare in coffee but possible if water or surfaces used were contaminated. Causes nasty food poisoning.
Bacteria need moisture, warmth, and nutrients to proliferate. Coffee left sitting out provides suitable conditions. Just a small amount of initial contamination can quickly multiply to dangerous levels after 4+ hours.
Will Reheating Coffee Kill Bacteria?
Simply reheating old coffee is not sufficient to make it safe to drink again. Some bacteria that grow in stale coffee produce heat-resistant toxins and spores.
Reheating coffee may kill some bacteria, but not the dangerous toxins already formed. Other bacteria may survive reheating depending on time and temperature. And mold of course will remain present after reheating.
So while a quick reheat may make foul-tasting coffee more palatable, it does not negate any pathogens present. Reheating cannot make spoiled coffee safe again.
Can You Drink Cold Brew After It Sits Out?
Cold brew coffee naturally has higher acidity and lower pH than regular iced coffee. This makes it somewhat more resistant to bacteria growth. However, cold brew should still not sit out at room temperature for longer than 4 hours before potential contamination becomes a concern.
Drink cold brew within 3-4 hours of being brewed for optimal freshness and safety. Do not let it sit out overnight. And certainly don’t drink days-old cold brew.
Tips for Storing Leftover Coffee
To enjoy black coffee safely and enjoyably when you don’t finish it fresh, here are some storage tips:
Pour coffee into a sealed container
Minimize air exposure by transferring leftover coffee from mugs into a sealed thermos, stainless steel bottle, or jar with an airtight lid.
Refrigerate promptly
Chilled temperatures slow bacteria growth. Fridge your leftover coffee ASAP.
Consume within 3-5 days
Drink your stored coffee within 3-5 days for best quality. It will become unpalatable after about a week in the fridge.
Avoid room temperature storage
Leaving unfinished coffee sitting on the counter promotes rapid bacteria and mold growth.
Don’t reheat more than once
Limit reheating stored coffee to once, as multiple reheat cycles worsen flavor.
Following proper storage methods allows you to enjoy leftover coffee a bit longer and prevents waste. But do not drink old coffee that has been improperly stored at room temperature for many hours.
Can You Make Coffee With Old Coffee Grounds?
Used coffee grounds should not be reused to brew a new batch of coffee. Brewing fresh coffee requires freshly ground beans with intact oils and aromatic compounds.
Previously brewed grounds are depleted of flavor, and will result in very weak, bitter coffee. The grounds may also have absorbed odors and moisture that could contribute off-flavors.
So reuse your coffee grounds for creative purposes like composting, scrubbing, dying, gardening, etc. But don’t try to eke out a second brew from them.
Signs Your Coffee Has Gone Bad
Here is a summary of the signs that indicate your leftover coffee has spoiled and needs to be discarded:
– Sour, rancid smell
– Mold growth (dots, film, fuzz)
– Change in color
– Unpleasant taste
– Gritty, uneven texture
– More than 4 hours at room temperature
Trust your senses – if old coffee smells, looks or tastes off to you, do not drink it. A fresh brew is cheap and easy to make again. When in doubt, throw it out.
Conclusion
Black coffee that’s been left sitting out can usually be safely consumed if it has sat for less than 2 hours at room temperature. Thecoffee may start to taste more bitter and stale after 1-2 hours but is unlikely to become hazardous.
However, after 4 or more hours of sitting, previously brewed coffee is no longer safe or palatable. Bacteria levels may multiply to dangerous amounts. Mold growth, off-odors, and unpleasant flavors also detract from the coffee after several hours.
To enjoy leftover coffee and avoid waste, store it promptly in a sealed container in the fridge and consume within 3-5 days. Do not leave coffee sitting on the counter for extended periods, and never drink coffee that smells or looks abnormal or has set for over 4 hours.
As a general rule of thumb, drink coffee within an hour of brewing for optimum taste and food safety. Discard any coffee that has exceeded this time, and brew a fresh, hot beverage instead. With proper handling, you can both reduce waste and enjoy delicious coffee safely.
