Apparently amateur chemistry isn’t for everyone. Especially not the thousands of mixologists and bartenders across the world who’ve been recommending and serving Moscow Mules in mugs with copper interior coming into contact with the acidic drink. Potentially poisoning drinkers in trendy restaurants from Portland to … Portland. The Iowa Alcoholic Beverages Commission recently reminded everyone of this fact by publishing a bulletin recommending against the use of copper mugs in serving alcoholic beverages with a low pH (acidic).
The Washington Post picked up on the story and put together a decent piece on the matter, reporting what chefs and most culinary aficionados have known for a very long time – acidic foods (drinks too) can leach copper into the finished product. It’s why copper pots and tomato sauce don’t mix – and why the Iowa ABC decided to remind everyone that the FDA’s regulates against the use in the Food Code:
4-101.14 Copper, Use Limitation.
(A) Except as specified in ¶ (B) of this section, copper and copper alloys such as brass may not be used in contact with a FOOD that has a pH below 6 such as vinegar, fruit JUICE, or wine or for a fitting or tubing installed between a backflow prevention device and a carbonator.
(B) Copper and copper alloys may be used in contact with beer brewing ingredients that have a pH below 6 in the prefermentation and fermentation steps of a beer brewing operation such as a brewpub or microbrewery.
But why is the low pH drink verboten when low pH mash in copper kettles for brewing allowed under the Food Code. Turns out there’s good reason for it. So in case you’ve ever wondered why copper leaching into your mash is accepted:
The steps in beer brewing include malting, mashing, fermentation, separation of the alcoholic beverage from the mash, and rectification. During mashing, it is essential to lower the pH from its normal 5.8 in order to optimize enzymatic activity. The pH is commonly lowered to 5.1-5.2, but may be adjusted to as low as 3.2. The soluble extract of the mash (wort) is boiled with hops for 1 to 22 hours or more. After boiling, the wort is cooled, inoculated with brewers yeast, and fermented.
The use of copper equipment during the prefermentation and fermentation steps typically result in some leaching of copper. Because copper is an essential nutrient for yeast growth, low levels of copper are metabolized by the yeast during fermentation. However, studies have shown that copper levels above 0.2 mg/L are toxic or lethal to the yeast. In addition, copper levels as low as 3.5 mg/L have been reported to cause symptoms of copper poisoning in humans.
Therefore, the levels of copper necessary for successful beer fermentation (i.e., below 0.2 mg/L) do not reach a level that would be toxic to humans. Today, domestic beer brewers typically endeavor to use only stainless steel or stainless steel-lined copper equipment (piping, fermenters, filters, holding tanks, bottling machines, keys, etc.) in contact with beer following the hot brewing steps in the beer making process. Some also use pitch-coated oak vats or glass-lined steel vats following the hot brewing steps. Where copper equipment is not used in beer brewing, it is common practice to add copper (along with zinc) to provide the nutrients essential to the yeast for successful fermentation.
And a good reminder that the FDA has much more to do with your brewing and production than you think.