Engine Room Hooch was an alcoholic beverage made by members of Starfleet. Engine Room Hooch was most often produced on board starships, but would at times be produced in other Starfleet installations as well. Engine Room Hooch was usually made by a member or members of the Engineering department. (Star Trek: The Original Series novel: Vulcan's Glory)
In the 2250s, the production of the drink was officially frowned upon by Starfleet, but in actual practice a blind eye was often turned to it as many senior officers would themselves partake of the beverage themselves. In his Starfleet Academy days, Montgomery Scott and a number of other students made the drink in a generator room at the academy.
Shortly after being posted to the USS Enterprise, Lieutenant Scott began producing Engine Room Hooch. He located his still near the warp core. Shortly after production was begun, a dilithium crystal cracked, which bombarded the still with gamma radiation, and contaminated the beverage produced within. It resulted in the alcohol being very potent; a couple drinks resulted in extreme intoxication. As a result, the still and the bottles were confiscated and destroyed. Chief engineer Caitlin Barry announced that production of Engine Room Hooch would no longer be tolerated. (Star Trek: The Original Series novel: Vulcan's Glory)
By 2379, Engine Room Hooch was available, although not publicized, in the USS Prometheus' mess hall. The still in which it was made was, in spite of the name, not located in engineering but instead in Cargobay 3 and was maintained by the ship's chef, Tedak, and not a member of the engineering staff. Knowledge of the still was common place onboard but was not officially acknowledged or encouraged even though many members of the crew including Captain MacLeod, Lieutenant commander ch'Rimosi, and Chief Gunn were known to occasionally enjoy the beverage. (Star Trek: Prometheus)