From Distillers Wiki
A Fermenter is a container or vessel of food grade quality, in which yeast ferments fruit or grain. A fermenter can be any thing from a 5 gallon bucket to a multi thousand gallon vessel. But for the Home Distiller any thing from 5 gallons to 15 gallons is more than enough do to the fact that our stills are no larger than a 15 gallon boiler. Fermenters usually have an airlock which allows carbon dioxide to escape, but prevents air from entering the container. In an enviroment rich in oxygen, the yeast will use aerobic respiration which does not produce alcohol.