A recent report highlighted the dangers of drinking a Moscow Mule out of a copper mug, in which it's traditionally served. It was, in a word, a buzzkill. But don't worry—you can still enjoy the fantastic cocktail without worrying about being poisoned.
On July 28, the Iowa Alcoholic Beverages Division issued a report to remind businesses serving alcohol in copper mugs of "federal guidelines and state regulations" about how the material can be used. Copper, the report continues, is not permitted to come into contact with any acidic material with a pH lower than 6.0. That's because acidic materials, like vinegar, fruit juice, or wine, can cause copper from the surface to leach into the substance and high concentrations of copper "are poisonous and have caused food borne illness."
Granted, this leaching can happen in copper plumbing that conducts water with a lot of carbon dioxide, or when brewing beer, the report continues. But Moscow Mules present a particular threat because they are made of a combination of vodka, ginger beer, and lime juice, which puts their pH "well below 6.0. This means that copper mugs that have a copper interior may not be used with this beverage," it reads. (The report echoes guidelines from the Food and Drug Administration; see page 111.)
The Internet, naturally, was in a tizzy. Publications seeking to their protect cocktail-loving readers pushed headlines like "Heads up, Moscow mule lovers: That copper mug could be poisoning you" and "Copper Cocktail Mugs Could Give You Food Poisoning, Experts Warn" and even "Moscow Mules could be slowly poisoning you."
Here's the thing, though: There's only a risk of copper leaching into your Mule if the cup is made of pure copper or brass (an alloy of copper and zinc). Most copper mugs, however, are lined with another metal, such as nickel, tin, or stainless steel. Some mugs are actually made of stainless steel but plated or finished to give the appearance of copper.
Eating food prepared in copper pots and pans, or off a copper plate, is not uncommon and usually doesn't pose a risk. The issue only arises with acidic substances. Still, perhaps it's best to skip the pure copper cups specifically marketed to contain your Moscow Mule.
If the Moscow Mule and copper combo is such a risk, why the heck are the two paired in the first place? If history is to be believed, it was a stroke of chance—the owners of the bar where the drink was invented started engraving the cups to sell with the drinks as souvenirs, according to a 2007 article in the Wall Street Journal. The material of the cup seems to have little effect on the taste of the drink.
In short, you probably don't have to worry too much that your favorite summer cocktail is going to make you sick. But if the copper mug you're drinking out of has a copper interior, maybe ask to switch to a glass just to be safe.
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