Coffee that has gone cold can be one of the most annoying things inside a freezing office. There are moments when I am so focused on my work that I forget my steaming cup of Joe. There is always the option to brew another cup, but as someone who was raised never to waste a single drop, I always opt to reheat it.
So, can you microwave coffee? Putting your coffee in a microwave might be the quickest way to reheat it, and it is perfectly safe to do so! Unfortunately, your coffee will taste different because of the coffee’s composition and the changes it undergoes at the molecular level once it is reheated. Check out our explainer on can or should you microwave milk for coffee.
The Coffee’s Flavor Gradually Weakens
Coffee beans contain several volatile compounds, such as aldehydes, pyrazines, and phenolic compounds, to name a few, and they are mostly responsible for the coffee’s delicious flavor and immaculate aroma.
The problem is due to their low boiling points; they gradually evaporate from the moment the beans are picked from the plant up until they go into your cup. It doesn’t help that the roasting and brewing process often include high temperatures, so a significant amount of these volatile compounds will be gone before you can enjoy your java.
These chemical changes persist as these compounds continue to evaporate in your cup. Eventually, once it cools down, you are left with a lifeless beverage that is a tad bitter, slightly oily, and more acidic. Unfortunately, this bitter flavor is enhanced once you reheat it in a microwave.
The Coffee’s Bitterness Will Linger
Now we are introduced to non-volatile compounds, meaning it doesn’t evaporate easily and, more often than not, won’t or very slowly undergo a change at room temperature. Chlorogenic acid is one of coffee’s non-volatile compounds, and they are responsible for the bitterness that blends well with the volatile compound’s flavor profile.
Don’t get me wrong; they do undergo a chemical change when exposed to heat, notably during the roasting process when they break down into quinic acid and caffeic acid. These byproducts are also responsible for the bitterness and astringency of your cup of Joe.
The problem is there is bound to be chlorogenic acid left in your coffee, and it will remain undisturbed until you reheat it in a microwave. The microwave’s heat encourages the production of quinic and caffeic acid and vaporizes the remaining volatile compounds; hence the complex flavor profile of your cup of Joe will disappear. Sure, this will make a hot cup of java, but a bitter and slightly more acidic one at that.
On a positive note, caffeine is a non-volatile compound, so reheated coffee will have the same caffeine content as freshly brewed Joe. Reheated coffee will perk you up; it just won’t taste as good.
Reheating Coffee In A Microwave
The next question is how long you should reheat your coffee in a microwave and how high the temperature should be. Assuming the cup is half-empty, you can reheat it for about 20 to 30 seconds at about 150°F or by setting your microwave to medium or medium-high heat.
I reheat it for 15 to 20 seconds to retain as much flavor as possible and limit the bitterness. You don’t need too hot of a drink if you just plan to sip it all up, anyway. Also, a piece of advice, if you are going to microwave coffee, is to make sure your mug is microwave-safe – metallic cups will explode.
Counterbalancing The Drawbacks
If you really like your java steaming hot, you can reheat it for as long as 45 seconds. You can always add something fatty such as creamer, milk, or even butter, to enhance the flavor. Sweeteners such as sugar or honey are also good at offsetting some of the bitterness.
For instant coffee, you can add a teaspoon more to rejuvenate the cup. As I see it, the greater option is always just to brew yourself another cup if you have the time.
Another way, perhaps the best method, to reheat your coffee is using a stovetop kettle as you have full control of the temperature, which will allow you to retain some of the coffee’s flavors, and you can observe it easily. You can top up your coffee with hot water, but if it’s instant, you’ll probably want to add a little more coffee, so it’s not diluted.
Don’t even think of brewing coffee and continuously warming it up on your stovetop. This will gradually and surely vaporize any remaining flavor, and you will just be left with hot but bitter java, not to mention it is a waste of energy to do so.
They say prevention is better than cure. I suggest you brew a cup of Joe in smaller quantities if you are the type who can’t finish a cup in one sitting. If you like a bigger cup, try storing your coffee in an insulated cup or tumbler.
Our round-up of the do ceramic mugs keep coffee hot might also be helpful.
FAQs On Can You Microwave Coffee
Can microwaving your coffee affect your health?
The radiation from a microwave cannot alter a food or a beverage’s chemical breakdown. It just makes the water molecules vibrate to heat it quickly. The chemical change that happens when you reheat your coffee is due to the increase in temperature and not directly because of the electromagnetic radiation itself.
Can You Microwave Cold Brew Coffee?
You can microwave cold brew, although I don’t see a reason why because it is best enjoyed cold. Still, we can be thankful because the taste will be the same if you microwave it, albeit warmer. You can check out our guide on microwaving cold brew coffee to learn more!
How Long Before My Hot Coffee Goes Cold?
It usually takes around 30 to 40 minutes before coffee reaches room temperature. By this time, a significant amount of the coffee’s flavor and aroma are already lost. Be advised that an insulated mug or tumbler can keep your coffee warm for about three to four hours, but the gradual loss of flavor continues.
Can You Microwave Coffee More Than Once?
Yes, you can, and it is perfectly safe. However, you have to be wary of how long the coffee was sitting out all day, as it might have already gone stale. Take note that if your coffee has dairy products, leaving it out for too long will make the milk curdle and turn your beverage sour!