Of course, drinking freshly brewed coffee will always be the best. But what if our only option is to drink that morning coffee in the afternoon? The coffee community has reached a consensus on the shelf life of roasted coffee beans, but what about the products made from these coffee beans?
Generations and generations of coffee consumers have pondered this question, but to no avail, with some suggesting that freshly brewed coffee lasts as little as an hour and others up to half a day.
How long coffee remains appetizing is subjective, but in my opinion, after experimenting with drip-brewed coffee, it is 3 hours.
Does brewed coffee spoil over time?
A common misconception regarding the shelf life of brewed coffee is that coffee is almost all water, and water does not spoil. Like any other food, coffee spoils because, although it is mostly water, we also extract the organic compounds, acids, and oils that make coffee taste like coffee.
Coffee is a warm and humid environment full of organic compounds. For this reason, it is also a great breeding ground for bacteria, especially if the coffee is left uncovered on the countertop.
But, coffee and caffeine are antibacterial; how is it possible that bacteria can survive there?
Caffeine and coffee are antibacterial; some studies even find that caffeine kills E. coli. However, a recent scientific study from the University of Valencia found colonies of caffeine-resistant bacteria in drip trays of the Nespresso coffee machine:
Our results reveal the existence of a diverse bacterial community in all sampled machines and a rapid colonization process of coffee leaching.
Note: The above study refers to the drip trays of Nespresso coffee machines, which are exposed to the elements for days or weeks before being cleaned.
And while I have been unable to find any conclusive research on microbial growth in brewed coffee, most people seem to agree that anything within four to five hours of brewing is completely safe.
From personal experience, I have drunk day-old coffee more times than I’d like to admit, and nothing bad has happened to me… yet. So, even after 24 hours, coffee can be drunk without the risk of getting sick.
How long does it take for brewed coffee to stop tasting good?
In most cases, the best temperature range for tasting coffee, which professional coffee critics agree, is 55 degrees Celsius. At this temperature is when the acidity and sweetness of the coffee can be tasted.
In addition to the flavor properties, at this temperature, the coffee is hot enough for the aromatic molecules to vibrate rapidly and be released from the coffee, thus completing the flavor, which is a combination of taste and smell.
If the coffee has cooled to room temperature for too long, the flavor of the coffee has not gone anywhere but is not accentuated by the lack of odor. At this point, the molecules do not oscillate and vibrate as quickly as before, so the coffee has lost most of its aroma.
Although this is not all bad since the lack of aroma brings out the coffee’s acidity, sweetness, and general flavor. And this is why cooling it to room temperature is often my favorite way of drinking it.
Oxidation of brewed coffee over time
But like everything in life, good things don’t last forever, and there is a time limit when coffee starts to taste bad. This is due to a chemical process known as oxidation. Oxidation was a term first used by Antoine Lavoisier to refer to the reaction of a chemical substance with oxygen.
It was later realized that the loss of electrons caused this oxidation, and now the term is extended to all types of reactions in which electrons are lost and gained, regardless of whether oxygen is involved.
In the case of coffee, it is exposure to air and oxygen that leads to oxidation. While the free hydrogen ions in our coffee contribute to the acidity before oxidation, once it combines with oxygen and forms water, this reduced acidity and increased ph level of the coffee is perceived as bitter, not fresh or rotten.
Experimenting with the taste of coffee brewed after hours
To test my taste buds, I brewed some coffee with a drip cone and let it come down to room temperature (23°C). I then took a sip every 15 minutes and found that after three and a half hours of brewing was the limit for me. Every sip I took after 3.5 hours felt excessively bitter and empty of flavor.
You can drink coffee up to 24 hours after you prepare it with your coffee maker, and nothing will happen to you. However, its taste will get worse as time goes by. For me, 3 and a half hours is the limit when coffee starts to taste bad, but it may be different for you.
I occasionally drink coffee from the day before, but I wouldn’t dare drink coffee older than that for health reasons.
Remember that coffee goes rancid much faster at higher temperatures, so if leftover coffee is stored in the fridge, it will keep its flavor longer.