The material of the mug is said to keep the drink nice and cold while even improving the taste, per Moscow Copper. While that may be true, the mug could do more harm than good. In 2017, a restaurant manager in Iowa named Todd Brooks, who served up Moscow Mules in glasses rather than copper mugs, explained that the softness of the copper mixed with the acidity of the cocktail could make drinkers sick (via WQAD). Brooks wasn’t the only Iowa resident choosing glass over copper. That same year, Iowa’s Alcoholic Beverages Division posted an advisory on the topic, noting that copper could contaminate the drink. The entire state banned the use of copper mugs for serving Moscow Mules.
Food and drinks that have a pH below 6.0 are banned from coming in contact with copper, based on the FDA’s Model Food Code. “The pH of a traditional Moscow Mule is well below 6.0. This means that copper mugs that have a copper interior may not be used with this beverage,” the advisory bulletin read.
While copper could keep your drink frosty, you may want to opt for another receptacle the next time you order a Moscow Mule. WebMD explains that while some copper can be beneficial for your well-being, in the long run, people can suffer such symptoms as diarrhea, dizziness, nausea, headaches, and eye, nose, and mouth irritation.