The Effects of Heating Coffee The impact of reheating on your morning coffee is likely something you've previously observed. It affects the taste, which is why.
Coffee will naturally and unavoidably get more bitter after sitting and reheating, which is not something anyone really wants.
"Unfortunately, a chemical reaction that occurs regardless of the type of coffee, brewing method, or heating method is the primary cause of reheated coffee's tendency to taste bitter.
Your coffee will taste more bitter as a result of this process. Ryan Ludwig of Counter Culture Coffee explains, "This is what happens even if you don't heat the coffee, just let it sit for a long time."
The physics of how heat may turn coffee bitter, according to Ludwig, basically comes down to the acids in coffee that affect its flavor and scent.
One type of acid included in the beverage is chlorogenic acid, and Ludwig claims that its breakdown is the issue.
Over time, chlorogenic acid decomposes into quinic and caffeic acids. The chlorogenic acid is broken down considerably more quickly when your coffee is heated.
Sadly, both of these have a bitter flavor. To put it in perspective, quinic is the same acid that gives tonic water its distinct bitter taste.