Doing a Google search for “reheating coffee” seems to mostly yield the same advice: Don’t do it. At best, it ruins the flavor. At worst, it’s purported to cause cancer (which is a myth, but yikes!). I was curious about just HOW bad reheated coffee tastes, so when I had some leftover coffee, I thought I’d give it a try.
I made a batch of Coffee del Rey’s Guatemala Huehuetenango in my Chemex, and drank some hot. It was wonderfully inviting, with a milk chocolate and marshmallow aroma, and it was deliciously sweet (without any sugar or milk!). What a great start to the day… *happy sigh*
After about 45 minutes, there was still some coffee in the Chemex, so I poured it into my mug and nuked in the microwave for 1 minute on high. It was steaming when it came out so I let it cool for just a bit.
Reheated coffee: Well, the best I can say is that it still tastes like coffee… but there is a sour note to the cup that wasn’t there before, and a very slight metallic taste on the finish. The chocolate and marshmallow flavors were gone. It’s not the WORST cup of coffee I’ve ever had, but considering how beautiful the flavors were freshly brewed, it was quite disappointing to taste how much the flavors had deteriorated. Honestly, I was shocked at just how much the flavor changed! I can see how people may have gotten the idea that they’re drinking cancer-causing agents if their coffee tastes sour and metallic.
Summary: Yeah, I have to agree with Google. If you care about the way your coffee tastes, don’t nuke your coffee when it gets cold.
Instead, here are two suggestions to try:
1) Prevention. For keeping your coffee hot as long as possible: I hear that Zojirushi thermoses can keep hot (and cold) liquids at temperature for a LONG time… Amazon has reviews from people saying they will put hot coffee in their Zojirushi at 9 AM and the coffee can still burn their tongue if they are not careful at 3 PM. Brew your coffee normally and then transfer it to this thermos to enjoy piping hot for hours.
2) Transfiguration. Make coffee ice cubes for cooling down iced coffee: If you enjoy drinking iced coffee but dislike the way ice cubes water it down, try freezing your leftover coffee in ice cube trays. Two problems solved!