The Moscow mule — that Instagram-ready cocktail that has surged in popularity in recent years — has only a few ingredients: vodka, ginger beer, lime and ice. But perhaps the most crucial component of the drink is the copper mug in which it’s almost always served, beverage aficionados say.
Now, public health officials are warning that those mugs could be poisoning you.
An advisory bulletin from Iowa’s Alcoholic Beverages Division notes that, in keeping with Food and Drug Administration guidelines, copper should not come into contact with acidic foods with a pH below 6. That includes vinegar, fruit juice, wine and, yes, a traditional Moscow mule, whose pH is “well below 6.0.” the bulletin says.
“When copper and copper alloy surfaces contact acidic foods, copper may be leached into the food,” the division notes.
Symptoms of copper poisoning include abdominal pain, diarrhea, vomiting and jaundice, according to the National Institutes of Health. “Sudden (acute) copper poisoning is rare,” NIH says. “However, serious health problems from long-term exposure to copper can occur. Severe poisoning can cause liver failure and death.”
Most chefs and food scientists already know not to use copper (or copper-plated) pots and pans for acidic recipes like tomato sauce, not only for health reasons but for the ways in which “reactive” cookware can alter the flavor of a recipe. Food editor Emma Christensen broke down the differences between reactive and nonreactive cookware in a good primer for TheKitchn.com here:
Ceramics and stainless steel are considered nonreactive. While these don’t conduct heat very well and tend to have “hot spots,” they won’t interfere with the chemical structure of the food in such a way that changes the look or edibility of our food. … Aluminum, copper, iron, and steel (not “stainless”) are all reactive. They conduct heat very efficiently, and therefore, do a great job of cooking our food evenly. However, these metals are reactive with acidic and alkaline foods. If you’re cooking with ingredients like tomatoes or lemon juice, your food can take on a metallic flavor, especially if the cooking time is very long. Light colored foods, like eggs, can develop gray streaks.
The same reactions occur when copper surfaces come in contact with acidic drinks. The instinct to separate copper from acidic drinks may not be as apparent simply because copper cups haven’t been commonly used as a beverage vessel. Until now.