The drink ― made with vodka, ginger beer and lime juice and famously served in a copper mug ― is under fire for supposedly having the potential to poison its imbibers.
The Iowa Alcoholic Beverages Division issued a bulletin warning people about the dangers of the copper mugs in which this cocktail is traditionally served. The bulletin states, “High concentrations of copper are poisonous and have caused foodborne illness. When copper and copper alloy surfaces contact acidic foods, copper may be leached into the food.”
This sounds bad, especially to those who have copper mugs that aren’t lined with another nonreactive metal. Of Amazon’s top three bestselling copper mugs, two of them are not lined ― they are 100 percent copper. The third is lined with nickel. So contrary to popular opinion, not all popular Moscow mule mugs are lined with a non-copper material.
But even if you do have a 100-percent copper mug, how bad is the risk of being poisoned by your Moscow mule, actually?
Should you be nervous if you drink Moscow mules?
The answer, in short, is no.
We reached out to Trisha Andrew, assistant professor of chemistry and chemical engineering at UMass Amherst, and her first respons to HuffPost was, “I find the press release to be chemophobic fear-mongering.”
Andrews agreed to break it down for us with her chemistry expertise.
“Any time you have any liquid in contact with a surface, there’s a possibility that the container is going to be dissolved a little bit into the liquid,” Andrew told HuffPost. “With glass, the rate of dissolution is so slow that you’ll never see it in our lifetime.”
“But when you have metal container, like copper ― which is a little more dissolvable than other metals ― it happens more quickly.”
That’s why the bulletin advises that no foods with a pH below 6.0 should be in contact with copper. Copper is highly reactive, especially when in contact with liquids that have low pH levels. And lime juice has a pH level of 2.0-2.4, which is substantially lower then the bulletin’s recommended level.
A typical recipe for a Moscow mule contains 1/2 ounce of lime juice, 2 ounces of vodka, and 4 to 6 ounces of ginger beer.
It should be noted that vodka has a pH level between 6.0-7.0. In our own testing, our pH strips indicated that ginger beer’s pH is below 6.0, and the collective Moscow mule (including all ingredients and ice) rings in at a pH below 6.0. So the Moscow mule is indeed corrosive to copper. Andrew explains what that means.
“What happens is, especially acidic solutions solvate the atoms from the surface of the container into the solution and it makes ions,” explains Andrew. “Copper that’s dissolved is no longer copper in its metallic state, but it’s a copper(II) or a copper(I).”
“Copper(I) is known to be very toxic, it actually is used sometimes on the hauls of ships to prevent abalone from crusting on the surface,” Andrew elaborated. “But humans need copper(II) in some small amount in order to survive in their regular biochemical functions. Actually we have enzymes in our body that are part of our regular biological processes that have copper(II) as part of their chemical structure.”
In other words, copper is not all bad. That’s not to say we want to drink a glass of lime juice that’s been sitting in a copper vessel for days, but it does slightly soften the dangerous image that leaching copper can conjure up.
So what does that mean for the iconic Moscow mule mug?
“It’s been suggested that a concentration of 30 milligrams of copper per liter has been noticed to cause nausea in a small population of test subjects,” explains Andrew. “So the question is: over the duration of time that a Moscow mule sits in a copper mug, is that enough time and acidity to leach out 30 milligrams of copper per liter?”
Her answer will be a relief to you.
Even if you’re nursing the drink all night, “based on the dissolution rates, it’s just nonsensical,” Andrew stated. “You have to let the copper mug sit in straight lime juice for a few hours before you can even start to begin to worry about [copper poisoning].”
And even if you drink a liter of Moscow mules from pure copper mugs, which you probably shouldn’t, you wouldn’t even come close to reaching that 30 milligram limit.
Now, go ahead and enjoy yourself another round of Moscow mules. You deserve it after all this copper poisoning anxiety.