Real Dictionary

ferment
uncountable noun: Ferment is excitement and trouble caused by change or uncertainty.
verb: If a food, drink, or other natural substance ferments, or if it is fermented, a chemical change takes place in it so that alcohol is produced. This process forms part of the production of alcoholic drinks such as wine and beer.

ferment in American English
a substance or organism causing fermentation, as yeast, bacteria, enzymes, etc.
to be in the process of fermentation
to cause fermentation in
intransitive verb: to be fermented; undergo fermentation
noun: any of a group of living organisms, as yeasts, molds, and certain bacteria, that cause fermentation
transitive verb: to act upon as a ferment

ferment in British English
noun: any agent or substance, such as a bacterium, mould, yeast, or enzyme, that causes fermentation
verb: to undergo or cause to undergo fermentation