Carboy

A carboy is a large, narrow-necked vessel, traditionally glass but also made in durable plastic, used as a fermenter or a secondary aging vessel. The narrow neck limits the beer's surface area exposed to air, which helps during longer aging periods, and a rubber stopper with an airlock fits snugly over the opening to manage fermentation gas while keeping contaminants out.

Glass carboys are prized for being nonporous and easy to sanitize thoroughly, and they let you see exactly what is happening inside, but they are heavy, can shatter if dropped or thermal-shocked, and are awkward to move once full. Plastic carboys, usually PET, are lighter and safer to handle but are slightly more permeable to oxygen over long storage and can scratch more easily, which creates hiding spots for bacteria if not cleaned carefully.

A frequent mistake is lifting a full glass carboy by the neck alone rather than supporting the base, which risks cracking the neck under the vessel's own weight. Another is racking wine or a long-aging beer into a carboy that leaves a large headspace, which increases oxygen exposure during extended aging compared to a properly sized vessel or a top-up of similar liquid.