Carboys are used in all types of applications from laboratories, to storage of cleaning supplies, to collecting waste solvents. The materials used for these carboys is vast comprising of steel, copper, glass, and numerous forms of plastics. Ultimately whats required for fermentation of wine, beer, or saki is a sealable and non-permeable vessel that allows gases to escape, but not enter the container. Light and heat are other factors for the fermentation process, and these can be controlled based on the environment of features of the carboys, pales, jugs, containers, drums, or conical fermenters.
All of these various shapes, sizes, and materials will work for fermentation. However each have their advantages and each have their drawbacks. For example, will you be able to see the liquid during fermentation and get lost in the swirling currents of yeast activity? How many batches will the container really last, without compromising the flavor and out come of the home brew? Are you going to need to lift the vessel and disturb the flocculated yeast that have settled to the bottom along with the polymers, proteins, and tannins?
On the low end you could ferment in a 12 oz ball jar, it has been done. With some sort of airlock or lid at a minimum it allows for a place for the yeast to mix with the wort and release its gas. This will in fact produce beer. Some beers are actually created using natural yeasts (critters) that can be found in the air, thus removing the need for a lid at all.
On the other end of the scale there is temperature controlled, pressure capable, seamless welded, stainless steel conical fermentors. The top of the line models offer rotating racking arms to reduce sediment during draining, ball bearing valves for extracting yeast cultures, peep holes for viewing, all mounted on a stand that allows for easy transfer to kegs or bottles. Sounds delicious.
And then, there is the rainbow of options in between including plastic carboys including BetterBottle, Nalgene and other plastic composites. There is also a range of glass carboys and vessels. And yet to mention is the countless steel drums that are rarely found in homebrew stores, but offer the brew another option. As mentioned all of the options under the sun will have their advantages and disadvantages including durability, cost, leaching implications, ability for bacteria formation, weight, and size.
The following sections dissect the options giving manufacturers, costs, and options available.