Meaning of “ferment” - Learner’s Dictionary

ferment

verb [ I, T ] uk us /fəˈment/

If food or drink ferments, or if you ferment it, the sugar in it changes into alcohol because of a chemical process:

The wine ferments in barrels.
fermentation uk us /ˌfɜːmenˈteɪʃən/ noun [ U ]

(Definition of “ferment verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)