Okay, so what we’re talking about is coffee that has been brewed hot and slowly reaches room temperature. We’re not talking about cold brew coffee or hot brewed coffee that is quickly chilled, say with ice.

Now that we got that out of the way, here is what happens. From USA Today:

“As hot coffee cools, these lactones break down to become carboxylic and chlorogenic acids. These acids present themselves via a bitter/acidic flavor in the cup,” he said. “This combined with the oxidization that is also occurring as coffee cools down just makes for a super unpleasant taste most of the time.”

You know that taste; Bitter and acid mixed with a luke warm feel! Ugh! Even if you reheat the coffee it still tastes terrible.

So, what can you do to avoid that awful taste? Keep your coffee warm or just make a fresh pot!! No one deserves lousy coffee!!