Green’s Dictionary of Slang

pruno n.

[The Other Side of the Wall: A Prisoner’s Dict. (2000): ‘Pruno: Homemade alcohol, fermented juice, the classic prison drink. It is made by putting fruit juice, fruit, fruit peelings in a plastic bag with bread and/or sugar. The yeast in the bread along with the sugar helps ferment the fruit juice, fruit, or peelings. The plastic bag is usually placed down the toilet and secured so that it is not detected’]

1. (US prison) illegally distilled liquor.

[US]H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 30/2: PRUNO. Fermented prune juice.
[US]Goldin et al. DAUL 164/2: Pruno. (P) An alcoholic home brew concocted of prunes and sugar.
[US]F. Hilaire Thanatos 174: They sniff shoe glue and drink watered-down pruno—home brew—with a kick of a small frog and a four-day hangover.
[US]K. Scott Monster (1994) 286: We had just finished making a batch of pruno – jail-made wine.
[US]J. Lerner You Got Nothing Coming 163: In addition to making bread [...] the bakers also mass-produce ‘pruno,’ a potent alcoholic brew available in such fruity flavors as orange, apple, and peach.
[US]J. Stahl ‘Pure’ in Love Without 162: If Jesus was in lockdown, he’d turn the water into pruno.
[US]J. Stahl Happy Mutant Baby Pills 27: Pruno (that’s jailhouse hooch, made from fermented fruit, for you innocents).

2. attrib. use of sense 1.

[US]J. Stahl I, Fatty 202: Compared to the pain and sandness [...] a pruno headache was pleasant.