Vulcan brandy is a alcoholic beverage, produced by the Vulcans.
In 2377, after the Maquis took over USS Voyager (under the influence of Teero Anaydis's mind control), Chakotay offered Tuvok some freshly replicated Vulcan brandy before ordering him to fire a phaser at Captain Janeway (with nothing happening, as the phaser was defective) to prove his loyalty. (VOY: "Repression")