Iowa, as well as many other states, has adopted the federal Food and Drug Administration’s Model Food Code, which prohibits copper from coming into direct contact with foods that have a pH below 6.0.Examples of foods with a pH below 6.0 include vinegar, fruit juice, or wine.
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. 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 it seems to me that the acidity of a Moscow Mule comes from the carbonation of the ginger beer and the lime. It's reasonable to me that it's below 6 (and somewhere in the pH 3-4) range. But the question that I have is what is the threshold for copper toxicity? Thanks to a report from the Agency for Toxic Substances and Disease Registry, we have a sense:
Slightly higher thresholds for gastrointestinal symptoms were observed in two acute-duration repeated exposure studies in which subjects used a copper-containing water as their primary source of drinking water for 1 or 2 weeks (Pizarro et al. 1999, 2001). In the 2-week study, 60 women were given copper sulfate containing water to be used for drinking and cooking purposes. No significant alterations in serum biomarkers of liver damage (alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transferase) were observed in the subjects at the end of the study. An increased occurrence of nausea, vomiting, and/or abdominal pain was observed when the women were exposed to 3 ppm copper as copper sulfate (0.0731 mg Cu/kg/day) (Pizarro et al. 1999); no significant increases in the incidence of gastrointestinal symptoms were noted at 1 ppm (0.0272 mg Cu/kg/day). Nausea, vomiting, and/or abdominal pain were also reported by women ingesting water containing 5 ppm (0.096 mg Cu/kg/day) as copper sulfate or copper oxide for 1 week (Pizarro et al. 2001).Would I be willing to bet there was less than 3 ppm copper in a Moscow Mule that had been sitting in an all-copper mug on the counter for more than an hour? Probably not.
(Aren't we done with the Moscow Mule trend? I feel like it peaked two years ago? I dunno, I'm a beer guy myself.)