Vermouth

Vermouth was one of the ingredients used to make martinis.

When Jack Harkness prepared himself a martini while waiting for his ship to explode, he accidentally poured too much vermouth. (TV: The Doctor Dances)

Behind the scenes
While not explicitly stated in the episode, vermouth is an aromatised fortified wine — a white wine fortified to at least 16 percent alcohol and flavoured with botanicals (plants, barks, seeds and fruit peels). Vermouth can be drunk by itself (normally as an apéritif), though it is primarily used in cooking and as a cocktail ingredient.