An Etymological Dictionary of the German Language/Käse
Käse, m., ‘cheese,’ from the equiv. MidHG. kœse, OHG. châsi, m.; Lat. câseus (whence also OIr. caise), before the 5th cent. at the latest was adopted in the vernacular form câsius (variant căscus?) by the Teutons; comp. Du. kaas, AS. čŷse, E. cheese. It corresponds in Rom. to Ital. cacio, Span. queso; yet câseus was supplanted in the dials. at an early date by Lat. *formaticus, ‘(cheese) mould’; comp. Fr. fromage (Ital. formaggio). OIc. has a peculiar word for ‘cheese,’ ostr, in Goth. perhaps *justs (comp. Finn. juusto, ‘cheese’); the assumed Goth. *justs is connected etymologically with Lat. jus, ‘broth,’ OSlov. jucha, ‘soup,’ OInd. yûšán, ‘soup’ (comp. Jauche), the root of which is yu, ‘to mix,’ in Lith. jáuju, jáuti, ‘to mix (dough).’ From this collocation of terms it is probable that *justs is the OTeut. word for ‘cheese,’ and that the Teutons did not learn how to make cheese from the Southerners, but only an improved method of doing so when they adopted the term Käse from them. It is true that according to Pliny, Hist. Nat. xi. 41, the barbarians generally were not acquainted with the method; yet comp. also Butter.