How to (really, should you) reheat coffee?

I’ve gotten into an afternoon habit of late, of making a really big pot of spiced tea, or maybe it’s a tisane as there’s no actual tea in it, just a lot of cinnamon, turmeric, ginger, a pinch of chilli, coriander seeds, fenugreek seeds, fennel seeds – it’s rogan josh in a plunger. By the time I’m on my second mug of the arvo, it’s stone cold. At least it’s below body temperature. As it’s winter, I’m drinking this rogan josh tisane for the following ratio of 5% health, 35% flavour, and 60% hand warmer. I’m no tea snob, so I put that mug in the microwave and nuke it for a minute and a half. Does it lose flavour? Does it lose health benefits? Don’t care, I have a nice warm cup to hold onto and I’m feeling good.

I am a coffee snob. On principle, based on accepted truths in the specialty coffee world, I would never dream of reheating coffee. It’s just not done. I celebrate the change in flavour profile as the coffee cools, its molecules releasing and contracting, sweetening and mellowing in the symphony of thermodynamics. 

But now I question myself. What if I want a hot coffee?

If all you want is a hot coffee, by all means reheat that sucker. But if you’d like it to retain the succulent sweetness, silky mouthfeel and bright acidity you enjoyed just moments after brewing it, you have to take the following into consideration.

1. You can’t get the original flavour back. Brewed coffee’s flavour is attributed to the volatile molecules that are released through chemical reactions to temperature. As they evaporate, the break away, floating off, hopefully in the vicinity of your nose, telling your brain synapses that this molecule is like that other molecule from the Seville Orange you ate on the coast of Majorca. Once these molecules have been released, that’s it, they’re gone. No amount of reheating will entice them back from the atmosphere (or your nose) and into the cup. 
2. Bitterness will increase. Coffee contains high amounts of chlorogenic acids, which we perceive as bitterness. Some of these acids break down during the initial brewing, contributing to a balanced flavour profile, however on second heating, more of these chlorogenic acids break down, and with much of the initial brighter, aromatic volatile molecules having already flown the coop, the bitterness overpowers what sweetness was remaining.

But, if after all this you’ve decided that all you really want is a hot coffee – use the microwave. 

This method heats in a more homogeneous manner and is  quicker than the stovetop, giving less time and opportunity for even more aromatic compounds to leave.

So if you must, chuck your cold coffee in the microwave, heat it only to the desired drinking temperature and no more, give it a stir to ensure evenness of nukage, and there you have it. The best reheated coffee you could hope for.

 

*As we’re only talking about black filter coffee, we can park the discussion of the health and safety risks of reheating milk, but even still, use your commons. Don’t go reheating coffee that’s been sitting on your desk since Friday morning that’s been reheated twice already. Don’t do that.