You can spot a Moscow Mule cocktail from across the bar by its cheery copper mug, frosted with cold on the outside, filled with ginger beer, vodka and a wedge of lime.
The Alcoholic Beverages Division of the State of Iowa is concerned with the interaction of those contents with the copper mug and issued an advisory bulletin in late July to warn of potential health risks.
The Iowa advisory says the state has adopted the US Food and Drug Administration's model Food Code, "which prohibits copper from coming into direct contact with foods that have a pH below 6.0." That includes liquids like fruit juice, vinegar, wine and Moscow Mule cocktails.
The Alcoholic Beverages Division reminds businesses they cannot serve Moscow Mules in mugs with a copper interior.
Mugs aren't the only place where copper might be able to leach into acidic foods. The US National Library of Medicine notes, "large amounts of copper from unlined cookware can cause nausea, vomiting, and diarrhea."
Moscow Mule fans don't necessarily have to give up on the traditional look of the drink. There are plenty of mugs on the market that feature copper on the outside and a different material on the inside, such as stainless steel.