An Etymological Dictionary of the German Language/Saft
Saft, m., ‘sap, juice,’ from the equiv. MidHG. saft, usually saf, OHG. saf (gen. saffes), n.; corresponding to AS. sœp, n., E. sap, Du. and LG. sap. Its connection with Lat. sapio (OHG. sęven, sęppen, MidHG. sęben, ‘to observe’) and sapor is conceivable on account of OIc. safe, ‘sap,’ provided that an Aryan root sap, sab (comp. Sans. sadar, ‘nectar’) seems possible (on the other band, Gr. ὀπός, ‘sap,’ and OSlov. sokŭ are not allied). The prevalent view that AS. sœp and OHG. saf were borrowed from Lat. săpa, ‘thick must,’ is unsatisfactory.