Carboy

A carboy or demijohn is a rigid container with a typical capacity of 20 to 60 L (5 to 15 gallons). Carboys are primarily used for transporting liquids, often water or chemicals.

They are also used for in-home fermentation of beverages, often beer or wine.

Brewing

In brewing, a carboy or demijohn is a glass or plastic vessel used in fermenting beverages such as wine, mead, cider, perry, and beer. Usually it is fitted with a rubber stopper and a fermentation lock to prevent bacteria and oxygen from entering during the fermentation process.

During the homebrewing process, a primary carboy is used for fermentation. Once primary fermentation is complete, the beer is either transferred to a secondary carboy for conditioning or it can be transferred directly to bottles for conditioning. (This process of transferring is usually called racking.)

Polypropylene carboys are also commonly used in laboratories to transfer purified water. They are typically filled at the top and have a spigot at the bottom for dispensing.