Underberg® Bitters is a digestif made from herbs and gentian root. It doesn’t contain sugar, as other bitters do.
It is sold in small bottles wrapped in brown paper.
You need to sip it, or chug it.
Underberg Bitters were developed by a Hubert Underberg, who first brewed it commercially in 1846. As of 2005, the company is being run by Emil Underberg, the fifth generation.