The word ferment means a commotion or excitement. Consider that the fermentation that turns juice or grain into alcohol is the result of the agitated development of bacteria, and then you can better appreciate the word's meaning.
While you might be more familiar with the verb ferment, referring to the natural process that produces alcohol, the word is also used as a noun, giving the same type of boiling emotion to people or events. If you keep in mind that the root of the word is fevere, meaning "to boil or seethe," you get a vivid picture of the ferment experienced at a political rally where tempers run high.
Primary Meanings of ferment
cause to undergo fermentation
a process in which an agent causes an organic substance to break down into simpler substances; especially, the anaerobic breakdown of sugar into alcohol
a state of agitation or turbulent change or development
be in an agitated or excited state
n a process in which an agent causes an organic substance to break down into simpler substances; especially, the anaerobic breakdown of sugar into alcohol
a slow kind of alcoholic fermentation at a temperature low enough that the yeast cells can sink to the bottom of the fermenting liquid; used in the production of lager
a violent kind of alcoholic fermentation at a temperature high enough to carry the yeast cells to the top of the fermenting liquid; used in the production of ale
the process whereby fermentation changes grape juice into wine