Why Does Reheating Coffee Taste Bad?

hot coffee being poured

I don’t know anyone who likes their coffee reheated, but some people only like coffee at just the right temperature. If it gets a little cold they pop it in the microwave. Reheated coffee never tastes as good as fresh coffee, but why does reheating coffee make it taste so bad?

Essentially, reheating coffee changes the chemical makeup of the coffee.  This affects both the taste and aroma of coffee.  Since we use both senses to taste, this chemical change is primarily what makes it taste bitter and bad.

This is the main reason why reheated coffee tastes bad, but there are other reasons why reheating coffee is not the best way to deal with cold coffee.  If you love coffee, but hate when it gets cold, keep reading for more details on why reheated coffee tastes lousy and what to do when your cup of coffee gets cold.

How Does Reheating Coffee Make it Taste Bad?

The flavor of coffee is generally determined by how long it’s roasted.  A dark roast coffee is roasted at a higher temperature and for a larger period of time. This tends to cook off some of the natural flavors of the coffee bean. Some of the same principles that apply to roasting (or heating the coffee beans) also apply to reheating them.  The longer a bean is roasted, and the more time it spends under heat, the more bitter it will taste. This is part of the reason reheated coffee tastes bad. However, this isn’t the only reason.

The Science Behind why Reheated Coffee Tastes Bad

Most of the flavor of coffee actually comes from its aromatic compounds. Love the smell of coffee?  You might not realize this, but what you smell is a large part of what you taste.  Your average cup of coffee contains over 1000 chemicals responsible for its wonderful aroma.  These chemicals include caffeoylquinic acids and feruloylquinic acids, which is the reason why coffee can have an acidic flavor.  When you roast or heat coffee, these chemicals break down. As the chemicals break down, they leave an acidic byproduct behind.

The more times you heat coffee, the more these chemicals break down. This means your coffee has fewer aroma compounds and more acidic byproducts.  This is why when you reheat a cup of coffee you don’t smell the lovely scent of coffee in the room like you do when you brew it.  Most of the aroma compounds are lost in the process of reheating and replaced with acidic tasting byproducts that just taste bad.

Is Reheated Coffee Bad for You?

Even if you hate reheated coffee, you might still drink it reheated.  Your choices for when your coffee gets cold are limited.  Pitch it, brew another pot, or warm it up in the microwave. You might have been told that reheating coffee is bad for you, but is that really true.

In general, reheating coffee only affects the flavor and aroma of the coffee,  It doesn’t change the chemical makeup to make it toxic or dangerous.  Your coffee might not taste as good, but it’s not going to hurt you.

Even if you reheat your coffee regularly, it’s not harmful to your health.  This might put your mind at ease, but it still doesn’t address the problems with how terrible reheated coffee tastes. There are a few ways you can reheat coffee so that it doesn’t taste as bad.

Ways to Reheat Coffee

Although reheating coffee generally isn’t the best way to drink coffee, there is more than one way to reheat coffee. Some reheating methods are better than others. The most popular and convenient way to reheat coffee is in the microwave, but you may be wondering if there are other better ways to do it.

Reheating Coffee in the Microwave

If you have absolutely no better way to reheat your coffee than using a microwave, timing is everything. Set your microwave for 20 to 30 seconds to reheat your coffee. Then check the temperature. If it’s not quite hot enough, microwave it for 20 seconds more. This way you don’t unnecessarily reheat your coffee longer than you need to and can retain some of the flavors of your coffee.

Reheating Coffee in the Coffee Maker

If you’re looking for a solution for warming up leftover coffee, reheating it in the coffee maker might sound like a good idea.  There are a few reasons why you shouldn’t reheat coffee in your coffee maker. Placing your coffee back on the warmer plate won’t bring the temperature up enough to reheat it. The alternative is to pour the coffee back through your coffee maker. Doing this is bad for your coffee maker, and rebrewed coffee doesn’t taste very good. Your coffee will end up with leftover coffee grounds in it, and lose a lot of its flavor. 

Reheating coffee on the stovetop

If you are at home, you can reheat your coffee on your stovetop.  Reheating coffee on the stove using a low temperature, allows you to reheat your coffee at a much lower temperature than your microwave. You can reheat it slowly to warm it up, preventing some of the chemical breakdowns that happen during reheating.

What is the best way to reheat coffee?

We all know that coffee is best when it’s freshly brewed, sometimes you need to reheat it.  Most people use the microwave to reheat coffee because it’s convenient, but the microwave is one of the worst ways to reheat coffee.  

Overall, the best way to reheat coffee is on the stove. Using the stove allows you to warm your coffee up slowly and at a lower temperature. This preserves more of the flavor than other reheating methods.

Does Reheating Coffee Remove Caffeine?

Many people mistakenly believe that reheating coffee breaks down the amount of caffeine in coffee. While there are chemical reactions that happen during reheating, caffeine is not broken down in the same way that other coffee compounds are.

As a rule, reheating caffeine does not remove caffeine from coffee. Caffeine requires an enormous amount of heat to decompose. Even when it is heated at high temperatures, it doesn’t evaporate, it dissolves. It doesn’t get cooked out of the coffee.

In order to remove caffeine from coffee, coffee manufacturers use a complicated process that chemically removes the caffeine. It is not an easy process, and not something you can do by simply reheating your coffee.

Better Options for Reheating Coffee

The best way to deal with cold coffee is not to reheat it at all.  There are going to be times when this isn’t an option, but if you find yourself reheating your coffee regularly, consider these options.

Brew Smaller Pots

Instead of reheating it, consider brewing your coffee in smaller quantities. If you tend to drink your coffee slowly, fill your coffee mug halfway instead of filling it up. 

Top off Your Coffee

Restaurants go around refilling your cup for a reason. Nobody wants cold or reheated coffee. If you find your coffee has gotten cold, brew a small 1 or 2-ounce pot in your coffee maker, and top off your cup.

Use a Coffee Thermos or Insulated Cup

A coffee thermos is a better option than reheating. Even if you’re at home, a coffee thermos might be the way to go. It insulates your coffee so the chemicals remain intact.  You can drink it out of the thermos or pour a small cup at a time.  

Pour Your Coffee Over Ice

Cold coffee is surprisingly delicious and a better option than reheating it.  If your cup of coffee gets cold, pour it over ice. If you normally drink your coffee black, you might need to add a little sweetener or milk to your coffee, but iced coffee is a really great option for leftover cold coffee.

Tim S.

Tim loves roasting, brewing, and experimenting with coffee. After years of perfecting this craft, working as a barista, and owning a small coffee service in college, he has decided to share his knowledge with the world.

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