The Collaborative International Dictionary of English v.0.48:
Fermenter \Fer*ment"er\, n.
an apparatus for carrying out fermentation by a liquid
suspension of microorganisms; a fermentation tank; as, an
Note: Laboratiory and industrial fermenters are usually
equipped with a means of stirring the contained liquid
so as to avoid settling of the fermenting organisms,
and often have other, sometimes elaborate, mechanisms
to control conditions of the fermentation, such as
temperature, degree of aeration, or pH. The main
structures of large industrial fermenters are typically
made of steel.