A carboy is a rigid glass container that many sons and daughters of wine making immigrants came to accept as a fixture of their home, or that of their family.

Back in the day, glass carboys were the only method to carry many liquids and beverages before the invention of plastic decimated the industry.

At one point in American history there were over 75 manufacturing facilities that dedicated their workforce to build stronger, safer and more reliable carboy carriers.

It was a smart business decision, as glass often breaks when handled roughly. Keep in mind this is before shock absorbers were as advanced as today.

So if your business relied upon the successful delivery of a liquid via a glass containment vehicle, you didn't want any breakage. Nor do home wine making enthusiasts want today. Beside losing the cost of materials, serious physical harm has been known to occur when dropping a carboy.

According to Wikipedia, a carboy is a container with a typical capacity of 5 to 15 gallons (20 to 60 L). However, most wine enthusiasts really call a 3, 5 or 6 gallon vessel a Carboy and anything larger a Demi John.

Back in the day, Carboys were primarily used for transporting fluids, often water or chemicals. While they are used for such today, the volume has great ely reduced industry demand as other, less expensive materials were developed through advanced plastics.

In the the case of the home wine maker they are also used for in-home fermentation of beverages, often wine and beer. It is not unusually for home wine making enthusiasts to have several to a dozen glass carboys used mostly for secondary fermentation and aging.

Brewing

In brewing, a carboy is also known as a demijohn. It is a glass or plastic vessel used in fermenting beverages such as wine, mead, 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.

The word carboy is from the Persian qarabah (قرابه), from Arabic qarraba, "big jug".

Carboys come in various volumes ranging from 3.8 to 24.7 liters. The term carboy itself usually refers to a 19 L carboy, unless otherwise noted. A 4.5 liter carboy is usually called a jug. A 57 L carboy is usually called a demijohn (in the Philippines, "dama juana".)

"Demijohn" is an old word that formerly referred to any glass vessel with a large body and small neck, enclosed in wickerwork. The word may derive from the name of a Persian town, Damghan, but this is not supported by any historical evidence. According to The Oxford English Dictionary the word comes from the French dame-jeanne, literally "Lady Jane", as a popular appellation. This is in accordance with the historical evidence at present known, since the word occurred initially in France in the 17th century, and no earlier trace of it has been found elsewhere.

In Britain, demijohn refers to a 4.5 liter glass brewing vessel.