What is a Carboy?

What is a Carboy? The official definition of a carboy is that it is a large container for holding liquids.

In layman’s terms, a carboy is a glass jug very similar in shape to the bottles used in water coolers you see in many office spaces. They can range in size however the most popular hold 6 gallons (22 liters) of liquid.

Although carboys can be used for holding and transporting various liquids they are typically used for making beer, wine, cider, and even mead by people in their homes.

The History of the Carboy

Prior to the invention of plastic and the subsequent manufacturing of plastic bottles, containers, and buckets, glass bottles, and jugs such as carboys were how the majority of liquids were stored and transported.

Carboys were used to such a degree that there were many successful businesses that’s sole purpose was to manufacture carriers for carboys in order to protect them from breaking while being transported.

Various Sized Carboys

You will find many different sizes of carboys capable of holding various volumes of liquid. The standard size for most homebrewers or winemakers is the 6 gallon (22 liter) size. However, for people who prefer to brew smaller or larger batches you can purchase carboys that hold anywhere from 1 gallon all the way up to 15 gallons ( 4 liters – 57 liters).

In most circles, the 6 gallon or 19-liter size is referred to as a carboy, whereas the 1 gallon or 4-liter size is called a jug, and the larger sized 15 gallon or 57-liter size is called a demijohn.

Used for Primary Fermentation 
A picture of a carboy of wine with the tile of what is a carboy.
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When used for brewing it is the vessel used during the fermentation process. The liquid that the brewer wishes to ferment is transferred into the carboy and mixed with the brewer’s yeast. The act of adding the yeast to the carboy is referred to as pitching the yeast.

A rubber stopper with an airlock is fitted into the mouth of the carboy in order to prevent oxygen or bacteria from entering into the carboy and infecting the batch. As the yeast consumes the sugar within the liquid it converts it to alcohol and CO2. The CO2 is allowed to escape out of the airlock.

It is important to leave adequate headspace in your carboy. When the liquid begins to undergo the transformation into alcohol the activity within the vessel can be quite vigorous and foam called Krausen will form and rise to the top of the carboy. If there is not enough headspace the krausen can clog the airlock and leak out causing a large mess. Typically a 6 gallon carboy is used when fermenting a 5 gallon batch of homebrew.

If the brewer is expecting an overly active or vigorous fermentation a blow-off tube can be used instead of an airlock. A blow-off tube is a piece of rubber tubing approximately 1-2 feet long that one end is inserted into the mouth of the carboy in place of the airlock and the other end into a bucket filled with sanitizer.

Primary fermentation can take anywhere from 4 – 14 days. Once it has been completed the homebrew is now either transferred to bottles (or a keg) or to a secondary carboy.

Used for Secondary Fermentation & Conditioning

After the primary fermentation stage is over some brewers will then transfer over to a secondary carboy for what is called secondary fermentation. There are a few reasons people do this.

1) Although in the majority of cases all of the fermentation should occur in the primary fermenter, sometimes there will be a need for additional fermenting, typically these are brews that are higher in alcohol, typically over 5.5% ABV. Although you can leave the brew in the primary to continue fermenting, brewers who transfer to a secondary carboy believe it will produce a cleaner brew with fewer chances of developing off flavors as it is removed from the residue called trub leftover from primary fermentation.

2) If you are making a lager beer you will always need to transfer it to a secondary carboy for the lagering phase.

3) When a brewer wishes to add flavors to their brews such as fruit or oak they will typically rack to a secondary and add the flavoring to it.

4) When a brew is racked to a secondary all of the sediment from the primary is left behind which results in a clearer end result.

5) Most alcoholic beverages taste better with age. Beer and wine turn out much better when given time to condition and mature. Although this conditioning does also occur after you have bottled your brew it is believed by many that letting it have time to mature some in a secondary carboy will result in a better tasting and looking end result.

Frequently Asked Questions

Why use a carboy instead of a bucket?

There are a few benefits to using a carboy instead of a bucket. The first is that since carboys are a bit smaller than buckets they leave less room for oxygen to get in and oxidize the beer or contaminants to infect it. The second reason is that it is transparent, you can see everything that is taking place within without having to open a lid as you do on a bucket. They allow you to easily see what is taking place with the fermentation without risking introducing contaminants by opening the lid of a bucket.

What can I brew in a carboy?

You can brew pretty much any type of alcoholic beverage that you want to make. They are primarily used for wine, however, are very popular with brewers who make mead, beer, and hard cider also.

How do you fill up a carboy?

Oxygen at the start of fermentation is actually a good thing, so you do not need to worry about splashing the liquid around and oxygenating it at this point. The mouth of the carboy is small as compared to other fermenters so it can be a challenge to get the liquid into it, the two methods employed by most brewers is to either place a funnel into the mouth of the carboy and pour the liquid into it or to use silicone tubing that you either attach to a siphon or directly to the spigot of your brewing kettle.

Additional Reading:  How to clean a carboy.

The Final Word

As we have seen, a carboy is simply one of the options you have available to you as a brewer when it comes to choosing the type of fermenting vessel you wish to use. It has many benefits and is a time-proven way to ferment your brew.

P.S. If you make your own beer or have ever thought of doing so, take advantage of the offer on the side of the blog to grab some delicious recipes to try out.

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