late 14c. (intransitive), from Old French fermenter (13c.) and directly from Latin fermentare "to leaven, cause to rise or ferment," from fermentum "substance causing fermentation, leaven, drink made of fermented barley," perhaps contracted from *fervimentum, from root of fervere "to boil, seethe" (see brew, v.). Transitive use from 1670s. Figurative use from 1650s. Related: Fermented; fermenting.

early 15c., from Middle French ferment (14c.), from Latin fermentum "leaven, yeast; drink made of fermented barley;" figuratively "anger, passion" (see ferment, v.). Figurative sense of "anger, passion, commotion" in English is from 1670s.