Fer·ment n.
 1. That which causes fermentation, as yeast, barm, or fermenting beer.
 Note: ☞ Ferments are of two kinds: (a) Formed or organized ferments. (b) Unorganized or structureless ferments. The latter are now called enzymes and were formerly called soluble ferments or chemical ferments. Ferments of the first class are as a rule simple microscopic vegetable organisms, and the fermentations which they engender are due to their growth and development; as, the acetic ferment, the butyric ferment, etc. See Fermentation. Ferments of the second class, on the other hand, are chemical substances; as a rule they are proteins soluble in glycerin and precipitated by alcohol. In action they are catalytic and, mainly, hydrolytic. Good examples are pepsin of the dastric juice, ptyalin of the salvia, and disease of malt.  Before 1960 the term "ferment" to mean "enzyme" fell out of use.  Enzymes are now known to be globular proteins, capable of catalyzing a wide variety of chemical reactions, not merely hydrolytic.  The full set of enzymes causing production of ethyl alcohol from sugar has been identified and individually purified and studied.  See enzyme.
 2. Intestine motion; heat; tumult; agitation.
    Subdue and cool the ferment of desire.   --Rogers.
    the nation is in a ferment.   --Walpole.
 3. A gentle internal motion of the constituent parts of a fluid; fermentation. [R.]
    Down to the lowest lees the ferment ran.   --Thomson.
 ferment oils, volatile oils produced by the fermentation of plants, and not originally contained in them. These were the quintessences of the alchemists.