Warm up coffee? This can have health consequences. Reheating is also a health risk, according to a study by Food Research International.
If coffee with milk has been standing for a long time, it can clot and bacteria can form. The microwave heating mechanism does not kill these bacteria in food. The outer layer of the coffee is heated first, then the inner layer. The temperatures are therefore not high enough to combat any bacteria. Incidentally, heated foods from the microwave are “basically harmless,” according to the Association for Nutrition and Dietetics.