The famed Moscow mule cocktail contains just four ingredients: vodka, ginger beer, lime, and ice. But if you’re not careful, your Moscow mule could also deliver a fifth, deadly ingredient to the drink and your body—poisonous high concentrations of copper.
The drink is typically served in a copper mug.
According to an advisory bulletin from Iowa’s Alcoholic Beverages Division, copper should not come into contact with acidic foods with a pH below 6.0, which includes the delicious beverage known as the Moscow mule.
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“High concentrations of copper are poisonous and have caused foodborne illness,” the bulletin reads. “When copper and copper alloy surfaces contact acidic foods, copper may be leached into the food. Carbon dioxide may be released into a water supply because of an ineffective or nonexistent backflow prevention device between a carbonator and copper plumbing components. The acid that results from mixing water and carbon dioxide leaches copper from the plumbing components and the leachate is then transferred to beverages, causing copper poisoning. Backflow prevention devices constructed of copper and copper alloys can cause, and have resulted in, the leaching of both copper and lead into carbonated beverages.”
That doesn’t mean you have to stop drinking Moscow mules out of their traditional mugs, however. You just need to make sure your copper mugs are lined with another metal—usually nickel or stainless steel.
“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 bulletin notes. “However, copper mugs lined on the interior with another metal, such as nickel or stainless steel, are allowed to be used and are widely available.”
So inspect those mugs, buy new ones if you have to, and drink away!