The Best Way To Reheat Cold Coffee (Hint: It's Not In The Microwave)
There are few absolute certainties in life, except when it comes to coffee. We can say with absolute, unyielding truth that cold, lukewarm coffee is the worst. Iced coffee? Excellent. Hot coffee fresh from the pot? Even better. Cold, room-temperature coffee? Horrendous. Why? What is it about cooling coffee that makes it so unappetizing? There are a few reasons.
As coffee sits, on or off a heat source, the process of oxidation occurs. Oxidation in coffee is like rust on a car; it deteriorates. Exposure to the air, as well as the oxygen in the water, makes the coffee stale and increases its pH levels. These higher levels create bitterness and break down the flavors that made the coffee so rich. One of the reasons we drink coffee hot is that the heat masks the bitterness that is already present through oxidation. But the longer the coffee sits away from heat, it slowly cools to room temperature, and the more bitter it becomes.
What's to be done? Naturally, you're going to want to reheat your coffee. You might think the best way to do that is to put your mug in the microwave for a quick reheat. Think again. Microwaving coffee is not the way to go if you want to revive your brew to its original power. Despite the convenience of the microwave, the best way to go about reheating your cold coffee is to return it to the stove.
Low and slow on the stove
Here's the reason you want to avoid the microwave: it kills flavor. Quite literally, the radiation inside the microwave causes coffee's natural, volatile compounds to be released, thereby giving the drink that bitter, burnt taste. You'll get that hot cup of coffee back, but it's going to be even more bitter and flavorless. Plus, you'll probably burn your tongue.
Instead, the best way to reheat your coffee is on the stove over low heat. You can do this in a small pot or a tea kettle, it doesn't make any difference. It's the heat and patience that make all the difference. Patience is hard to practice when it comes to coffee, but it really pays off here. While it's not going to taste the same, because the compounds are ever-changing, the lower heat is your best shot at preserving whatever aromas and flavor your coffee has left. Plus, it helps avoid the ultimate tragedy: burnt coffee.
You'll know your coffee is back up to heat when wisps of steam start dancing off the top of the liquid or out of the kettle spout. If you like to be really specific, you're looking to hit between 120 to 140 degrees Fahrenheit on a food thermometer. While others may encourage you to start again or abandon your cold coffee, rest assured it's okay to reheat your coffee. By doing it on the stove, at least it's hot and retains some of its flavors. And that, at the very least, makes it drinkable.