The Iowa Alcoholics Beverage Division recently issued a warning against drinking out of copper mugs. The mugs are commonly used to serve Moscow Mules, an alcoholic drink made with vodka, lime juice, and ginger beer. Are you really at risk of copper poisoning by using copper mugs? Let’s take a closer look.

The Letter Of The Mug Law

The Food and Drug Administration prohibits copper from coming into direct contact with food that has a pH of less than 6.0. The reason is that copper is highly reactive compared to other metals.

Acidic foods are more likely to speed up corrosion. The concern is that over time some of the copper may deteriorate and be consumed with the beverage. Lime juice has a pH 0f 2.0 to 2.5, which is significantly more acidic than the recommended pH limit of 6.0 (lower pH equals more acidic).

Exactly How Acidic Are Moscow Mules?

The amount of lime juice used to make a Moscow Mule is minimal compared to the other primary ingredients: vodka and ginger beer. The pH level of ginger beer is below 6.0, and vodka ranges between 6.0 and 7.0.

What this means is that Moscow Mules are indeed corrosive to copper. The acidic solution of a Moscow Mule can ionize metallic copper into copper(I) and copper(II). Humans need small amounts of copper(II) to survive, but copper(I) is toxic.

Should You Throw Out Your Copper Mug?

First, you should find out whether or not your mug is lined with a metal other than copper. If it is, the lining should prevent any copper contamination. Even if your cup lacks a protective coating, the toxicity will likely be negligible.

According to Trish Andrew, assistant professor of chemistry and chemical engineering at UMass Amherst, “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].” Even if you’re drinking Moscow Mules out of the same mug all night, the chance of the drink becoming dangerous is small. What a relief! Drink your Mules responsibly.