This root was one of a surprisingly large number of roots Tolkien used for “juice”, appearing as ᴹ√SAB in The Etymologies of the 1930s with derivatives ᴹQ. sáva/N. saw “juice” (Ety/SAB). It might be a variant of (hypothetical) early root ✱ᴱ√WASA needed to explain the forms G. gwâs and ᴱQ. vasa “juice” in the Gnomish Lexicon of the 1910s (GL/44). The primitive form ᴹ✶sāba also appeared in a rough 1940 note with the word N. iofog “fruit drink”, though Tolkien ultimately decided the second element was derived from ᴹ√SUK “drink” (TMME/53).
Neo-Eldarin: For purposes of Neo-Eldarin, I would assume this root refers mainly fruit juice and pulp, as opposed to syrup and tree sap which would be derived from ᴹ√PIS.