Why You Probably Shouldn't Reheat Your Coffee In The Microwave

Unless you've specifically asked for an iced americano or a cold brew, a cooled-down cup of coffee can be extremely disappointing — it just doesn't hit the same. To reheat it, a logical remedy would be to pop it in the microwave — it's what you do for leftover takeout, so what's the difference, right? Well — using the microwave to reheat your coffee can actually make it taste worse than before. To learn more about why this method is better off avoided, Food Republic spoke with Eric Gantz, co-founder of Verena Street Coffee.

Gantz notes that your coffee's aroma is "the first thing to vanish" in the microwave, because "those sweet, fruity smells come from delicate compounds that break down fast under heat." Aromatic compounds are responsible for the tasting notes you can identify in coffee (think nutty, caramel, or earthy) — but they're extremely volatile. This makes them a terrible pairing for the microwave, which rapidly heats the coffee, quickly causing these compounds to evaporate and leave you with a dull, bland taste that doesn't reflect the coffee's original character. Moreover, when heated, the "acids that once gave it brightness start breaking down into harsher, bitter-tasting compounds," Gantz adds.

Even without the breakdown of compounds, the heat of the microwave can also alter our perception of taste. "When it's too hot, our taste buds naturally notice the bitterness more," Gantz told us. "That's why reheated coffee often tastes burnt or lifeless."

Many coffees are already naturally bitter — just compare darker roasts to lighter roasts, or robusta beans to arabica — so bitterness isn't always a bad thing. But tip the scale of bitterness too far in the wrong direction and your cup of java might become undrinkable, and that's exactly what a microwave does. When coffee is brewed, bitter compounds such as caffeine and acids are extracted, and when reheated at high heat in the microwave, you're essentially double-brewing your coffee, causing those bitter compounds to become more pronounced. "A few short bursts on low power are fine, but if you crank it up, those bitter notes dominate fast," Eric Gantz notes. "Use the microwave on low power and short bursts, stirring between rounds." If you find that your coffee tastes too bitter and you don't want to waste it, a dash of salt could be a quick solution.

As the microwave is such a volatile way to reheat your coffee, consider using softer, more controllable methods that help preserve its original taste and flavor. But it's important to remember that "once coffee cools, its balance is gone for good," Gantz says. "No amount of reheating brings that back." Regardless, you can still make it drinkable rather than acrid. One method that gives you greater control over the temperature is heating it on your stovetop, stirring gently over low heat until the coffee reaches a satisfying temperature — around 130 to 140 degrees Fahrenheit, according to Gantz.