This carbonator is made of stainless steel and has a copper finish, so the surface is probably made of real copper, also known as a high-quality special alloy.

It's made of stainless steel with a copper-coloured finish. It's neither plastic nor copper, but the finish is beautiful and looks like copper.

Corrigendum... the copper is "only" a colour, not a copper alloy, but also quite high quality :)