Hayami's term for the alcohol she has disguised by transferring into fruit juice jugs and cans. She twice foists these onto the Minami sisters and their friends, without revealing their actual provenance. This gets them heavily drunk, with all its attendant side-effects. While this allows for some temporary hilarity, eventually everyone just passes out, so it is unclear why Hayami does this. One possibility is raised in Minami-ke Episode 13 (Minami-ke Chapter 025), where she uses the opportunity to hit upon the not drunk Kana. It should be noted than her behavior could easily land her in jail.
It does not seem that any of her friends have figured out what she is doing, with the possible exception of Kana, who at the very least realizes there is something very wrong with the "juice".