Should I Use a Carboy Instead of a Bucket for Fermentation?

Whether to use a carboy or a plastic bucket during fermentation is one of the classic debates in the homebrewing community. As with most hotly contested topics, there are pros and cons to each method. Every homebrewer should experiment with multiple brewing methods to discover what works best for their own process based on their priorities regarding homebrewing.

While plastic buckets provide unmatched convenience, carboys are the preferred fermentation vessel for high-quality homebrewing because they maintain the kind of antiseptic, airtight environment that is required for safe and consistent fermentation.

Glass carboys are specifically designed to offer the best possible environment for fermentation, however there are a number of legitimate reasons someone might prefer a different vessel. Read on to find out more about specific concerns and to make your own decision on which choice works best for you.

Should you use a carboy or a plastic bucket for fermentation?

The answer to this question lies in individual preference, but the difference between the two choices comes down to this:

Carboys provide a number of distinct advantages that allow a homebrewer to produce the best possible results, but a plastic bucket offers a level of convenience that may be attractive to those without the proper space or resources to invest in a carboy. 

Pros of a Carboy vs. a Plastic Bucket for Fermentation

Carboys offer several advantages worth considering when selecting a fermentation container, the most significant being its ability to maintain an anaerobic, or low-oxygen, environment. Carboys have a bottleneck that reduces the surface area in contact with air and have entirely clear sides that allow you to check up on your ferment without having to take off a cover like you would with a bucket, which would allow fresh oxygen into your container. Letting too much oxygen into your brew can make your beer taste stale or introduce off-flavors, and using a carboy instead of a bucket is a great way to ensure that you get the best results every time.

If you choose a glass carboy, another advantage is that glass is nonporous and will not scratch easily. This means you can use more abrasive brushes to make cleaning easier, and you will not have to worry about bacteria colonizing the small holes or scratches in your container. What’s more, even unscratched plastic can sustain between 10-40 percent more bacteria than glass after a wash with hot, soapy water due to its porous chemical structure.

Glass also has no risk of leaking flavor-altering byproducts into your beer like the HDPE plastics used in many plastic buckets do

Cons of a Carboy vs. a Plastic Bucket for Fermentation

For all the benefits that carboys provide, there are a few pretty convincing reasons you might prefer to use a fermentation bucket. Glass carboys are cumbersome, heavy, and can be rather difficult to handle.

If you don’t have space to safely store a carboy, a bucket might be your best bet; since carboys are made of glass, they can shatter if stored or handled improperly. Glass carboys are also a much more expensive option, with a 6-gallon coming in around $45 on Amazon, as compared to these plastic buckets of the same capacity for around $20.

So if you decide to purchase a glass carboy, be sure to treat it as an investment.

What is the purpose of a carboy during fermentation?

A carboy is designed to maintain the kind of anaerobic environment needed for high-quality and consistent fermentation. Any good modern fermentation vessel will use an airlock to keep out oxygen and foreign contaminants in the air.

A carboy offers the additional features of a bottleneck design to minimize the surface area in contact with air and glass walls that allow you to check in on the fermentation process without letting any additional air into the container. 

Is a carboy necessary? 

While a carboy is not strictly necessary, it will vastly improve the quality of your beer. Over the course of history, a wide variety of fermentation vessels have been used, from vases and barrels to open troughs. Modern brewing is based on a tradition of maintaining an airtight and antiseptic environment to prevent off-flavors and foreign bacteria from developing.

So if you are looking for a safe and consistent brewing experience, a closed container with an airlock is essential. 

Should you use a glass or plastic carboy?

If you decide to use a carboy but are put off by its weight, a plastic carboy can be a great compromise. Plastic carboys are cheaper, lighter, and are still impervious to air. They are much more maneuverable and will not shatter. Another interesting reason you might prefer a plastic carboy is that you can install a spigot in the side of a plastic carboy to make it easier to transfer your finished product without the need for a siphon. 

Still, plastic carboys have some of the same disadvantages as plastic buckets; you’ll have to clean them quickly with nonabrasive cleaners to minimize the risk of bacterial growth, and you will want to be aware that PET plastic can leach trace amounts of antimony into your homebrew. They scratch easily and have a limited recommended lifespan, unlike glass carboys, which can safely be used for years.

Which is better for secondary fermentation: carboy or plastic bucket?

If you are re-racking your beer for secondary fermentation, a carboy is definitely your best choice. Secondary fermentation can last a lot longer than primary fermentation, so reducing air contact is even more important when finishing your beer. Additionally, the longer period of time spent in contact with the fermentation vessel means you should be especially aware of the chemicals your chosen container might leach into your brew. 

On the other hand, it is much more important to be able to see your beer during the primary fermentation than during the secondary maturation process, so if you can only invest in one carboy, it might be best to save it for your primary ferments so you can look out for the visual cues to re-rack your beer without introducing oxygen while the yeast is most active. For more information on the visual cues that primary fermentation is complete, read my report here!