Aldebaran whiskey

From Memory Alpha, the free Star Trek reference.

"It is… it is… It is green."

Aldebaran whiskey is a strong, green alcoholic beverage, favored by Guinan, who kept a bottle behind the bar in Ten Forward. It was a gift from her friend, Jean-Luc Picard.

In 2369, Data served Montgomery Scott the drink of Aldebaran whiskey, although he was unsure of its characteristics beyond its color. Scotty found this beverage quite satisfying and drank most of the bottle himself, although he shared a couple of glasses with Picard. (TNG: "Relics")

Data's description of the whiskey in "Relics" only as "green" is a nod to Scotty's same description of a drink in "By Any Other Name". Most likely, the drink in that episode was Aldebaran whiskey as well.

In 2371, Quark discovered an empty bottle of Aldebaran whiskey in his brother Rom's room that was taken from Quark's "private stock". (DS9: "Prophet Motive")

Several barrels of Aldebaran whiskey were kept in storage in several of Deep Space 9's cargo rooms. (DS9: "Explorers", "Distant Voices")

The green substance referred to as Aldebaran whiskey in the episode Relics was, in real life, the citrus-flavored Hi-C Ecto Cooler soft drink.