Why McDonalds Coffee Cups Say "Do Not Microwave”

You decide to swing through McDonald’s drive-thru to grab a cup of coffee to drink on your morning commute. You get to work and still have a half a cup left, but it’s cooled down quite a bit. What do you do? The cup says “DO NOT MICROWAVE.” Why? The obvious answer is that even though they can keep coffee hot for a short period of time, they aren’t microwave-safe. That’s because the paper cups may potentially crack, smoke, or catch fire if exposed to high heat inside the microwave. While you may never have noticed it, those paper cups are actually lined with a thin coating of wax, and the higher the temperature, the greater likelihood that the cup will melt if it’s placed in a microwave. If the wax melts, it could contaminate the coffee and pose a health risk for you. If you need to reheat your coffee, transfer it to a microwave safe cup first. If that’s not an option and you have no other choice but to reheat the coffee in the McDonald’s cup, heat it in the microwave for no more than 20 seconds.