It’s generally not recommended to drink coffee that has been sitting out at room temperature for longer than 4 hours. By 12 hours, the coffee will start to taste stale and may have bacterial growth that could cause food poisoning. However, if the coffee was kept hot in a thermos or airpot, it may still be safe to consume within 12 hours. The taste and safety depends on how it was stored.
How Long Can Brewed Coffee Sit Out?
Brewed coffee that is left sitting out at room temperature will start to go bad after a few hours. Here is an overview of coffee freshness over time:
Within 30 Minutes
Coffee is freshest within the first 30 minutes after brewing. The optimal time to drink coffee for full flavor and aroma is as soon as possible after brewing.
The coffee will start to taste flat and lose aroma after sitting out for 2-4 hours. It may still be pleasant to drink, but will lose some freshness. Many coffee experts recommend drinking coffee within 1-2 hours.
At room temperature, brewed coffee will start to taste stale and oxidized after 6-8 hours. The flavors and aromas degrade rapidly during this time. Bacterial growth may start after 6 hours.
By 12 hours, the coffee will taste very flat and unpleasant. Bacteria and fungi can start growing after several hours at room temperature, causing off tastes and food safety issues. Coffee is not recommended for consumption after sitting out overnight for 12+ hours.
So in summary, while coffee left out for 12 hours may still be safe to drink in small quantities if kept very hot, it will likely have an unappealing stale taste and is not recommended. Optimal flavor is within 30 minutes of brewing.
Why Coffee Goes Bad When Left Out
There are two main reasons brewed coffee goes bad and gets stale when left to sit at room temperature:
Oxygen causes the natural compounds in coffee beans to oxidize and degrade over time, leading to a flat, cardboard-like taste. This staling effect happens more rapidly at warmer temperatures.
The warm, moist environment of brewed coffee is an ideal breeding ground for bacteria and fungi after several hours. This can lead to mold growth and foodborne illnesses.
Some common bacteria and fungi that can grow in old coffee include:
- Bacillus cereus – Causes food poisoning symptoms like vomiting and diarrhea
- Pseudomonas aeruginosa – Opportunistic pathogen that can cause infections
- Candida – Yeast that causes visible mold/film on the coffee
- Aspergillus – Mold that produces toxic aflatoxins
The acidic nature of coffee inhibits microbial growth to some degree, but does not prevent it after extended periods.
Tips to Keep Coffee Fresh Longer
If you won’t be able to finish a pot of coffee within 30 minutes, here are some tips to keep it warmer and prevent it from going stale as quickly:
Use a Thermal Carafe
Brew coffee into an insulated thermal carafe rather than a glass or metal pot. Thermal carafes like Yeti, Hydro Flask, and Stanley keep coffee hot for hours while preserving the flavor.
Transfer to a Thermos
Pour leftover coffee into a preheated thermos or insulated stainless steel container. This preserves heat and freshness.
Warm on the Stovetop
Gently reheat any leftover coffee on the stovetop to keep it at an optimal drinking temperature longer. Take care not to boil or scorch.
Add Hot Water
Top off cooling coffee with hot water to maintain temperature. This also dilutes the brew, so may be best for black coffee drinkers.
- Avoid returning warm coffee to the carafe as it will speed cooling
- Discard any coffee that smells or tastes off
- Don’t leave coffee sitting at room temperature longer than 4 hours
Can Reheating Coffee Make it Safe?
Simply reheating coffee that has been left out overnight will not make it safe to drink again. Some precautions include:
Reheating May Not Kill Bacteria
Bringing coffee back up to a warm serving temperature will not destroy all potential bacterial contaminants. Some bacteria can survive reheating, especially if not heated to over 165°F.
Dangerous bacterial toxins and mold spores can persist even after reheating. Heat does not neutralize these chemical toxins once produced.
Reheating stale, oxidized coffee can give it a burnt, bitter taste. The flavors don’t return to fresh by reheating.
Safest to Brew Fresh
When in doubt, it’s safest to brew a new pot of coffee rather than trying to reheat questionable old coffee. The optimal taste and safety comes from fresh brewing.
Can You Drink Colds Brews or Iced Coffee After 12 Hours?
Cold brew and iced coffee last longer than hot coffee, but also have reduced freshness and safety after 12 hours at room temperature.
Fridge Storage Extends Life
Kept refrigerated, cold brew coffee can maintain decent flavor for up to 1 week. For iced coffee, fridge storage gives a 3-5 day freshness window.
Room Temperature Reduces Life
At room temperature, cold brew and iced coffee have similar shelf life to hot coffee. Bacterial growth, mold, and oxidation will occur within 12 hours.
Rebrewing Not Recommended
For cold brew concentrates, rebrewing with new coffee grounds is not recommended once contaminated. Discard old concentrate rather than trying to re-steep.
When storing cold brew or iced coffee at room temperature, drink within 4 hours and discard remainder. Don’t let it sit out overnight.
Can You Microwave 12-Hour Old Coffee?
Microwaving coffee that has been sitting out overnight is not recommended.
Won’t Improve Flavor
The microwave may reheat coffee to a drinkable temperature, but cannot reverse the stale, oxidized flavors that develop.
Can Increase Bacterial Growth
The “danger zone” temperature range of a microwave is ideal for spurring added bacterial growth. It won’t make coffee safe.
Can Cause Bitterness
Microwaving can extract bitterness from the coffee grounds. This pairs poorly with existing stale flavors.
Safest to Make Fresh
Microwaving old coffee is not a substitute for brewing a fresh pot. Stick to microwave reheating only for coffee that’s under 4 hours old. Discard older.
Can You Drink Brewed Coffee Left Out Overnight?
It is not recommended to drink brewed coffee that has been left out on the counter or hot plate overnight and has sat for 12+ hours. The coffee will likely have an unpalatable stale, bitter taste at this point and raises safety concerns due to bacterial growth in the warm environment. Rooms, countertops and office spaces in the 70°F range allow rapid bacterial proliferation and oxidation. For optimal flavor and food safety, brew fresh coffee every morning. Discard any pots that have sat out overnight.
Coffee that sits out all night oxidizes rapidly, taking on cardboard, rotten, or other off tastes. Reheating cannot restore fresh flavor. The taste is generally unpleasant after so many hours.
Bacterial Growth Risk
Harmful bacteria multiply quickly at room temperature given the warm, moist medium. Mold and yeast growth may also occur. These can lead to vomiting, diarrhea, and other symptoms if consumed.
Safest to Discard
Trying to salvage overnight coffee is not worth the risks. Stale, contaminated coffee can cause significant illness. Brewing a fresh pot each morning is the safest and tastiest option.
Exceptions – Coffee Safe for 12+ Hours
In some select cases, coffee may still be safe to drink after 12 hours if it has been carefully handled:
Kept Hot in Thermos/Airpot
Coffee stored in a preheated thermos, stainless thermal carafe, or commercial drip coffee airpot can stay hot enough to deter bacterial growth for up to 12 hours if well sealed. Taste is best within 6 hours.
Sealed Cold Brew Concentrate
Unopened, refrigerated cold brew coffee concentrate can last 1-2 weeks before opening. At room temperature, sealed concentrates may last 12-24 hours with some flavor loss.
Canned Shelf-Stable Coffee
Commercially packaged shelf-stable canned coffee is designed to stay safe at room temperature. Unopened cans have a shelf life of 9-12 months. Opened cans should be refrigerated and consumed within a week.
Boiled or Reheated to 165°F
Boiling coffee for 1-2 minutes or reheating to 165°F is sufficient to kill most bacteria. This can make coffee stored for 12 hours safe, though taste may suffer.
Signs Coffee Has Gone Bad
Look for these red flags that indicate brewed coffee has spoiled and should be discarded after sitting out too long:
- Sour, bitter, or funky odors
- Moldy, ropey, or slimy texture
- Visibly darkened color
- Fizzing, bubbling, or fermentation
- “Off” taste that is stale, rancid, or rotten
- Floating objects or particles
Trust your senses – if coffee smells, looks, or tastes unpleasant, err on the side of caution and throw it out. Don’t drink it.
Coffee Food Safety FAQs
Can old coffee make you sick?
Yes, drinking coffee that has been left out too long can make you sick. Stale coffee may contain dangerous levels of bacteria that cause vomiting, diarrhea, and other gastrointestinal illness.
Does reheating coffee kill bacteria?
Simply reheating or microwaving coffee does not kill all bacteria that could be present after extended sitting out at room temperature. Some may survive, especially if not heated to 165°F+ temperatures.
Is moldy coffee dangerous?
Yes, moldy coffee contains toxins that can cause allergic reactions and other health issues. Never consume coffee with visible mold growth.
Can bacteria grow in iced coffee?
Yes, iced and cold brew coffee still allow bacterial growth if left unrefrigerated for hours. Keep refrigerated and drink within 3-5 days.
What temperature kills bacteria in coffee?
Heating coffee to 165°F and maintaining that temperature for at least 1 minute will kill most harmful bacteria. Boiling for 1-2 minutes can also make coffee safe by killing bacteria.
The Bottom Line
Enjoy coffee within 30 minutes of brewing for best taste and safety. If it needs to sit out longer, store hot coffee in a thermos or insulated container and refrigerate any iced coffee. Coffee that has been left to sit at room temperature for longer than 4 hours will rapidly degrade in flavor and safety. After 12 hours, it is best practice to brew a fresh pot and discard the old coffee. Reheating stale coffee does not make it safe or palatable. With proper handling, coffee can be kept safe and delicious for hours. But when in doubt, remember – fresh is best!