Copper is a metal necessary to life. It is found in everything on Earth, from humans to water and rocks. It is an especially good conductor and is often used for electrical wiring. Because of this high conductivity, copper has the potential to keep a drink cold but only if the copper itself is first chilled.
The Best Material
Copper is a much better conductor than glass. It takes 0.84 kilojoules of energy to change 1 kilogram of glass by 1 kelvin. Copper requires only 0.39 kilojoules. This means that if a cold drink is in a room-temperature copper mug, the temperature of the copper will decrease faster -- and the temperature of the drink will increase faster -- than if it were in glass. But if the copper is first chilled, the drink will retain its coldness longer.
Proof in the Kitchen
Further evidence that copper can keep a drink cold is highlighted by serious cooks’ preference for copper pots and pans for cooking food. Copper’s high conductivity allows the fast transfer of heat, which means that a copper pan will heat quickly and precisely -- without the risk of hotspots. Therefore, a copper mug for a drink will chill rapidly and will transfer that coldness to a drink before the ice has a chance to melt.
Proof in the Bar
The copper mug was popularized in the 1940s with the invention of the cocktail, the Moscow Mule. According to cocktail historian David Wondrich, the new owner of Smirnoff and the owner of Hollywood restaurant Cock 'n' Bull, which made its own ginger beer, were looking for ways to increase sales. By adding lime and serving the drink in one of Butte Copper Company’s mugs, a very cold, sought-after cocktail was created.
Even if a copper cup is not chilled first, therefore not keeping a drink cold, there still may be a purpose to drinking out of a copper vessel. In India’s traditional Ayurvedic medicine, which is a natural, holistic practice, it is believed that drinking from copper has positive benefits, such as preventing aging, killing bacteria and energizing the body. These beliefs are not shared in Western medicine.