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Why You Should Stop Reheating Your Coffee in the Microwave ASAP


Slowly sipping on a cup of coffee is one of life’s simple pleasures. Nothing beats that warmth, comfort, and energy boost it gives you as you dive into your to-do list for the day… that is, until it gets cold. If you’re the kind of person who gets intensely focused on something, chances are you forget about your drink until it cools down and you need to make a trip to the microwave. Unfortunately, reheating coffee in the microwave has some serious downsides.  

As we all know from experience, microwaves don’t heat food evenly. Cold spots happen because the food heats up from the outside in, as The New York Times points out. This might seem like a simple inconvenience, but it could actually become a health hazard.  

Michigan State University reports that those cold spots in your food can harbor pockets of bacteria that don’t die after a few minutes in the microwave. You may be tempted to ignore those cold spots. After all, you probably haven’t gotten sick from them yet, right? However, microwaved food has been linked to foodborne illnesses in the past.  

In an article from the American Journal of Epidemiology, researchers investigated the source of a salmonella outbreak at a community picnic in Juneau, Alaska. They found that it was directly linked to the way party goers prepared their roast pork. Those who reheated the pork in the microwave became seriously ill, while those who reheated it in an oven or skillet did not. 

A salmonella infection or any other infection from coffee is rare, because we usually brew it fresh with hot water and drink it immediately. Still, some types of coffee drinks may put you more at risk than others. 

Cold brew, milk, and creamers can make things worse. 

Generally, plain black coffee is safe to drink even if it’s been sitting out for a few hours. It probably won’t taste that great, but it won’t wreak havoc on your immune system. The problems start when you add milk or creamer to your coffee or opt for a cold brew.  

Milk and other perishable products shouldn’t sit out of the refrigerator for more than two hours. In the summer, just one hour outside of the fridge can be enough for bacteria to grow. Thus, reheating coffee with milk in the microwave can become a recipe for disaster. The dairy may give rise to bacteria in your mug, and the microwave won’t heat that cup of joe evenly enough to destroy all of it.  

Cold brew comes with its own set of problems. It is made by steeping coffee overnight in the fridge or at room temperature. As a result, this type of coffee poses a safety risk because the water doesn’t get boiled, and the coffee sits at room temperature for a very long time. Cold brew is also slightly less acidic than hot brew. Acidic foods tend to be more resistant to spoilage, whereas foods with a higher pH spoil more quickly. If you enjoy making cold brew and then heating it in the microwave, you may be exposing yourself to a host of bacteria.  

If you are older, you may be more at risk than others. 

Food poisoning can happen to anyone regardless of age. However, adults over the age of 65 are more susceptible to foodborne illness. The CDC cautions that older adults are more likely to get sick from food poisoning because their immune systems aren’t as strong as they once were. Their bodies have a much harder time eliminating harmful germs and bacteria. In addition, older adults usually produce less stomach acid, which means certain bacteria may not die in the stomach. As a result, nearly half of adults over 65 years old end up hospitalized if they contract a foodborne illness like salmonella or E. coli.  

This doesn’t mean that you have toss your coffee after 30 minutes, but it does mean you should practice certain safety precautions to avoid getting sick. Try warming it up in a saucepan on the stove, for example. And if you still want to reheat your coffee in the microwave, make sure that it’s a hot brew and not a cold brew. If it had dairy in it, throw it out in an hour or two and start over with a fresh cup.  

You can also avoid the cold pockets from the microwave entirely by investing in a smart mug. Smart mugs are temperature-controlled cups that keep your coffee at the exact temperature you desire. These mugs are hand-washable and typically have a one to two-hour battery life, so you can enjoy your coffee at the perfect temperature for more than just half an hour. If you don’t feel like using something high-tech, you can also invest in a well-insulated travel mug, which will keep your coffee piping hot while you’re working or on the go.  

Above all, just remember to be more careful when it comes to reheating coffee. Practice safe sips!    

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