The idea of leaving an unfinished cup of coffee for hours or brewing and storing large quantities of coffee at a time may sound baffling to some, but these practices are commonplace for others. The reasons behind this can range from absentmindedness to convenience.
But as typical as these instances are, remember that the coffee brew is still a food product. And as such, subject to two parameters: quality and safety.
With that in mind, how long is too long? Let’s explore that in this article.
Coffee Oxidization Causes Bitterness
First, let’s talk about quality.
How long will a freshly brewed coffee preserve its flavor integrity? The consensus in many coffee circles is around the 30-minute mark.
Although not standardized, it’s a good rule of thumb. Coffee’s volatile nature means the aromatics will be best appreciated while the cup is still hot. This will be within 15-30 minutes.
But there’s more to coffee than aromatics. As the cup cools, the flavor also changes. Good quality coffee will reveal more of its acidity and sweetness at this point. This is evident, especially during cupping. If the coffee has off-flavors, the cooler temperature will make them stand out.
People who like to sip and savor their coffees can still extend that experience to an hour or 90 minutes.
Facts: Stale or fresh coffee?
- How long do coffee beans last in the cupboard?
- Roasted coffee beans will still taste good for 2-3 months if stored properly in the cupboard. Frequent and prolonged exposure to air impacts flavor quality, so be mindful of selecting containers for the beans.
- How long do coffee beans last in the fridge/freezer?
- Freezing coffee effectively lengthens the window of freshness. Lower temperatures slow down reactions that may affect coffee’s flavor. Roasted coffees extend up to a year or more following correct cooling and storage practices.
- How long are coffee beans good for?
- Unopened packs of roasted coffee beans can last till the declared expiration date on the packaging. There is no official shelf life for roasted coffee. But its flavor acceptability will be dependent on its storage.
Letting your brewed coffee sit out for longer would be a different story. The chemical composition of the brew is complex enough as it is. Leaving it at the mercy of fluctuating environmental conditions can mess up the flavor.
There’s little research on the mechanisms of brewed coffee’s flavor degradation. Because of the number of volatile compounds present in the brew that readily react with one another, it can be hard to pinpoint the specific reactants and reactions.
We’ve seen coffee makers with hot plates underneath the carafes to keep the brew hot. And it does a good job of that if nothing else. The continuous heat only speeds up reactions occurring in the coffee brew. And the byproducts of these reactions don’t necessarily taste good.
Aromatic components will be the first to go, leaving behind the less volatile compounds—those contributing to bitterness. Keeping the pot hot will break down these bitter compounds further. Soon that coffee will taste nothing but liquefied bitterness.
How To Keep Brewed Coffee Tasty for Longer?
So we’ve covered the short window of coffee’s flavor quality. The follow-up question would naturally be: is there any way to lengthen that window?
Remember that brewed coffee will be at its tastiest within 30 minutes of brewing. To preserve some of that flavor, we don’t need the coffee heated, we want it insulated.
Thermal containers will do just that. A good old Thermos can insulate coffee for several hours. It would be unrealistic to claim this will keep all flavors intact, but it offers the best compromise between taste and time.
Ensure your Thermos is squeaky clean before transferring your brew. Doing this will prevent the coffee from absorbing unwanted odors and flavors.
Planning on keeping it longer than just a few hours? Best to store your coffee inside the refrigerator. Using an airtight container would help keep off the odors of other food items.
Stale Coffee and Health
Let’s move to the second parameter: safety.
Many hours since brewing. That cup of coffee has long passed its peak in flavor quality, but would it still be safe to drink? Yes, it would.
Brewed coffee doesn’t have a lot of nutrients to support microbial growth. Plus, it has antimicrobial properties as an added defense. So if we leave brewed coffee under hygienic conditions for 24 hours, then there’s little cause for concern.
Recommendations online on storage time are often anecdotal in nature. There’s limited research on the shelf life of brewed coffee, so there is a lack of standardization.
Based on sensory evaluation, it established a shelf life of 10 days for coffee brews stored at room temperature (with oxygen) and 15 days (with oxygen) if refrigerated.
Leaving your coffee in dirty surroundings can increase the risk of microbial contamination. And that would be unsafe to drink. But beyond those conditions, coffee is yet to have an official shelf life.
Another scenario is if the brewed coffee has milk. In that case, the milk’s stability dictates whether the coffee would still be safe to drink. Generally, milk will only last for an hour outside in warmer temperatures; two if it’s cooler.
So far, we’ve only been talking about hot brewed coffee, but what about cold brews?
Cold brews have shown better flavor stability over time than their counterparts. Unfortunately, they also pose a higher food safety risk. Reasons include the lack of a heating process and the long extraction and storage time.
Typically, high temperatures act as a sterilizing agent. By eliminating that step in cold brew preparation, microbes present in the coffee equipment and container are not killed.
It’s best to control sources of contamination as much as possible. Even the person preparing it should be cautious of transmitting germs. The long extraction and storage times can encourage microbes to multiply and ruin the coffee.
With these risks in cold brew processing, it’s safer to consume it the same day it’s made. Prolonged storage periods are not yet advisable because of potential microbial contamination.
Top Featured image: Bex Walton | Flickr CC2.0
Under sanitary conditions, that day-old coffee would still be safe to consume. Some might even resort to reheating it. In any case, if the taste is unpalatable, simply brew a fresh one.
A study pointed to a shelf life of 10 days if stored at room temperature. However, this was done on only one coffee origin.
The same study showed that brewed coffee can last up to 15 days if refrigerated. Cooler temperatures slow down flavor degradation. But this effect may vary for different origins, roast levels, or brew methods.