Etymology
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ferment (n.)

early 15c., from Old 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.

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ferment (v.)
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" (from PIE root *bhreu- "to boil, bubble, effervesce, burn"). Transitive use from 1670s. Figurative use from 1650s. Related: Fermented; fermenting.
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fermentation (n.)

late 14c., in alchemy, with a broad sense; modern scientific sense is from c. 1600; from Late Latin fermentationem (nominative fermentatio), noun of action from past-participle stem of Latin fermentare "to ferment" (see ferment (v.)). Figurative use attested from 1650s.

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*bhreu- 
also *bhreuə-, *bhreəu-, Proto-Indo-European root meaning "to boil, bubble, effervesce, burn," with derivatives referring to cooking and brewing.

It forms all or part of: barm; barmy; bourn (n.1) "small stream;" braise; bratwurst; brawn; brawny; braze (v.1) "to expose to the action of fire;" brazier; Brazil; bread; breed; brew; broth; broil (v.2) "to quarrel, brawl;" brood; effervesce; effervescence; effervescent; embroil; ferment; fervent; fervid; fervor; imbroglio.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhurnih "violent, passionate;" Greek phrear "well, spring, cistern;" Latin fervere "to boil, foam," Thracian Greek brytos "fermented liquor made from barley;" Russian bruja "current;" Old Irish bruth "heat;" Old English breowan "to brew," beorma "yeast;" Old High German brato "roast meat."
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yeast (n.)
Old English gist "yeast, froth," from Proto-Germanic *jest- (source also of Old Norse jastr, Swedish jäst, Middle High German gest, German Gischt "foam, froth," Old High German jesan, German gären "to ferment"), from PIE root *yes- "to boil, foam, froth" (source also of Sanskrit yasyati "boils, seethes," Greek zein "to boil," Welsh ias "seething, foaming").
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boil (v.)

early 13c. (intransitive) "to bubble up, be in a state of ebullition," especially from heat, from Old French bolir "boil, bubble up, ferment, gush" (12c., Modern French bouillir), from Latin bullire "to bubble, seethe," from PIE *beu- "to swell" (see bull (n.2)). The native word is seethe. Figurative sense, of passions, feelings, etc., "be in an agitated state" is from 1640s.

I am impatient, and my blood boyls high. [Thomas Otway, "Alcibiades," 1675]

Transitive sense "put into a boiling condition, cause to boil" is from early 14c. The noun is from mid-15c. as "an act of boiling," 1813 as "state of boiling." Related: Boiled; boiling. Boiling point "temperature at which a liquid is converted into vapor" is recorded from 1773.

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cheese (n.1)

curd of milk coagulated, separated from the whey, pressed and used as food, Old English cyse (West Saxon), cese (Anglian) "cheese," from West Germanic *kasjus (source also of Old Saxon kasi, Old High German chasi, German Käse, Middle Dutch case, Dutch kaas), from Latin caseus "cheese" (source of Italian cacio, Spanish queso, Irish caise, Welsh caws).

Of unknown origin; perhaps from a PIE root *kwat- "to ferment, become sour" (source also of Prakrit chasi "buttermilk;" Old Church Slavonic kvasu "leaven; fermented drink," kyselu "sour," -kyseti "to turn sour;" Czech kysati "to turn sour, rot;" Sanskrit kvathati "boils, seethes;" Gothic hwaþjan "foam").

But de Vaan writes, "no etymology can be found which does not require some poorly-founded assumptions," and suggests a loan-word. Also compare fromage. Old Norse ostr, Danish ost, Swedish ost are related to Latin ius "broth, sauce, juice."

Earliest references would be to compressed curds of milk used as food; pressed or molded cheeses with rinds are from 14c. Transferred to other cheese-like substances by 1530s. As a photographer's word to make subjects hold a smile, it is attested from 1930, but in a reminiscence of schoolboy days, which suggests an earlier use. Probably for the forced smile involved in making the -ee- sound.

Green cheese is that newly made; the notion that the moon is made of green cheese as a type of a ridiculous assertion is from 1520s. To make cheeses (1835) was a schoolgirls' amusement of wheeling rapidly so one's petticoats blew out in a circle then dropping down so they came to rest inflated and resembling a wheel of cheese; hence, used figuratively for "a deep curtsy." Bartlett ("Dictionary of Americanisms," 1848) defines head cheese as "The ears and feet of swine cut up fine, and, after being boiled, pressed into the form of a cheese."

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