At the far side of a dimly lit bar, two bartenders share shots of an unknown brown liquid. They’re drinking fernet—most likely Fernet-Branca—and taking part in a well-known industry ritual often referred to as “the bartenders’ handshake.”

This bitter Italian herbal spirit can be found on the shelf of almost any rickety watering hole or high-end cocktail palace. From Milan and Argentina to San Francisco, Fernet-Branca has earned its place in the mixologist lexicon and built a culture all its own.