What Size Carboy Do You Actually Need For A 5-gallon Batch?

The more I brew my own beer the more I realize that the right equipment can seriously save you time and stress. I also know that sometimes I’d bought the wrong piece of brewing equipment because I didn’t know enough about the task I’d have to really use it for.

Most homebrew recipes will have directions for 5-gallon batches of beer, although you can brew a lot less or a lot more. However, you are most likely going to be brewing your homebrew 5 gallons at a time.

 So, what size carboy do you need to save you a lot of headaches down the road?

You want to have at least a 6-gallon carboy and could go even a little bigger. The general rule of thumb is that you want 20% of extra room for your beer to ferment. With 6 gallon carboys, you should have enough room and if you can find a larger fermenter, you may not even need a blow-off tube. 

The thing is that there are so many factors at play that will affect how much headspace you need in a fermenter.

There is no universal answer and you will have to choose the one that you feel the most comfortable with, but remember that in this case, bigger is better. 

You don’t want a blowout and waste some of your precious beer. You should read on below to learn more about why you need that extra space and how to do it. 

How much space your beer needs to ferment in?

What size carboy do you actually need for a 5-gallon batch?

You want to leave 20% of extra room for fermentation to take place. This is for a few reasons the first being that the krausen will need some headspace.

Krausen is not a waste product and actually plays a vital role in the production of beer.  Krausen, if you are wondering is a german word for curly that describes the foamy build-up on the surface that comes from the yeast fermenting, among others things. ( See my article here for more information).

The next reason is for your beer’s protection. This extra space will act as a gas barrier from the outside world. That is to say that as the yeast processes the fermentable sugars in your beer, the carbon dioxide it produces will fill the headspace and ward off any nasty oxidizing air.

When you use an airlock or blow-off tube, these pieces of kit will help keep this carbon dioxide barrier in the fermenter by only allowing excess gas to escape. This is only possible if you use the right amount of water, which you can learn about in my article here.

Also, more space means that beer will not be wasted through overflow and you can get the most out of your brew, which is the ultimate goal. What I mean here is the very frustrating situation where you look into your full fermenter and realize you still have plenty of beer waiting to be transferred in your brew kettle. Not that it ever happened to me, of course…..

For more detail on getting the correct amount of headspace in your fermenter, check out my full article.

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What will happen if the carboy is too small?

You may have a smaller carboy around the house and think yea my brew will fit in there and yeah it has space instead of getting a larger one. This is something that I highly don’t recommend you do.

There are a few issues that may arise from this. Firstly, is that your beer has a huge blowout which will make a mess in your house. Many a homebrewer has come home to realize that they had had a very energetic fermentation and not left an escape route for all that gas.

This is more likely to happen when there is less than 20% extra headspace in the carboy and if the yeast is a little bit too warm. This is only a small issue and not the end of the beer or world. Just mop it up and stick your airlock back in, and monitor it more closely.

In most cases, a blow-out does just mean krausen and beer all over your ceiling. However, if you are using glass carboys, you could be facing a more dangerous situation.

While it is rare that a carboy shatters from the pressure when it does happen you will lose your beer and the carboy at the same time. This is why some homebrewers I’ve spoken to never use glass at all. Unhappy memories I guess.

Another problem that may happen that is just as sad, is that the beer gets infected. It’s a common enough occurrence when you don’t have that gas barrier and so sort of bacteria may enter because the beer is exposed to the air. In the most extreme situations, you may lose the whole batch as well as the time you put into it. 

When it’s not nasty bacteria, it’s good old-fashioned air. By allowing pressure to build up and blow out your airlock or blow-off tube, the time between the explosion and you walk into your home brewery may be all it takes for oxidation to set in. Now your beer tastes like old cardboard and that won’t pair with many side dishes at all.

Always go bigger. 

New to homebrewing? Please feel free to read my ultimate guide to brewing beer at home and where to start.

Recommended Carboys for a 5-gallon batch

Big Mouth Bubbler (6.5 gallon)

I would say that for most homebrewers you will want to prepare for a 5-gallon batch, in which case having a carboy with a 6.5-gallon capacity is ideal. I really like Northern Brewer and the Big Mouth Bubbler is great. If you can, grab the straps and holster for it too which will make moving it around much easier. You can check this carboy out on Amazon for the latest deals and availability.

If you actually don’t want a carboy and prefer the classic fermentation bucket, then check out the Ale Pale version which is a great cheap alternative to a carboy.

Again, you can find this on Amazon which offers great deals and crazy fast shipping these days!

Can you ferment your beer in different carboys?

To simply answer the question yes, you can ferment your beer in separate fermenting vessels. There are some stipulations and a few things that you would need to work out though.

You would need the same amount of yeast for each of them and this could be hard to measure. For instance, if you had five 1-gallon carboys you would need to divey up the yeast equally, have the same amount of fluid in each of them, and the space to store them as well.

This is not mentioned all the sanitizing,  and transferring as well. You will also need to spend money  5 of each thing you choose like bungs, airlocks, blow-offs, etc.,  your best and cheapest bet is to just get one 6-gallon carboy and 1 of everything or whatever size you want to make. 

This being said, homebrewers are notoriously resourceful, so if you have to do this for a particular batch, be assured that it can work.

Another reason you may want to split your batch into several different carboys is that you are testing out different strains of yeast or perhaps experimenting with different quantities of hops for dry hopping. Don’t feel that you have to put all your beer into one vessel if the creative juices are flowing.

Do you need more space in primary or secondary fermentation?

These phrases can get a little confusing sometimes and the different phrases mixed together. Primary fermentation is pretty straight forward but sometimes secondary fermentation is confused with a second fermentation.

Just to be clear, primary fermentation normally describes the initial vigorous stages of fermentation, as well as the lag stage between pitching the yeast and the first visual signs of the yeast’s little dinner party.

After a while, the primary fermentation will start to slow down. The oxygen within the wort (now called beer after pitching) will have been depleted and most of the sugars used up. So, the yeast population is no longer expanding, giving off as much CO2, or producing lots of krausen.

This basically means the need for so much headspace isn’t a big deal at this stage. So when you rack the beer into the secondary fermentation you will have a higher risk of oxidation because you don’t have the added protection of a continual stream of escaping carbon dioxide.

Knowing when to switch is key to this step and can be tricky since it could be ready to switch in as little as 2 days. But for your average ales, this is between 2 and 4 days and for a lager between 4 and 10 days. Read my full article here to learn more about when you should switch the fermenters.

Can you use a bottling bucket as a fermenter?

Yes,  you can use a bottling bucket as a fermenter, it would just have to be big enough to hold it all and have room. Now you don’t want to use just any bucket I would think that since you are using a bottling bucket, it is food-grade plastic already.

You also would want to have a lid that not only fits but is airtight. If you bought the bottling bucket from a brew supply shop it may have a hole for an airlock or blow-off tube, but if you didn’t, you will have to drill one and make sure that it is sanitized well. In my experience, the pre-drilled ones always seem more airtight than anything I could ever drill myself.

If all this is done and you have enough room for the krausen to grow without overflowing, then go for it, but I would recommend going checking out this article for the finer point on using a bottling bucket for fermentation.

Are fermenting buckets better than carboys?

These both have their positives and negatives and there is no right answer to which one is better to brew with. I’ll lay out the case for each side and you can make your own choice. If you want even more in-depth articles on my more in-depth article here.

For the carboy

  • A big advantage of the carboy over the fermentation bucket is that it is transparent. You will be able to see the whole fermentation process to monitor and take notes on what is happening.  Those that say a fermentation bucket can do this as well are not wrong and maybe for the seasoned brewer, it is OK. But for those that are meticulous or just beginning to brew by being able to see when fermentation begins and ends will take out the guesswork. Observing the whole process lets you better understand what it is that you should be looking for at each of the specific phases during any given fermentation.
  • With the carboy, you don’t have to remove any lids which increases the chances of introducing bacteria and outside debris.  This also but doesn’t necessarily mean that the trub and krausen are disturbed and could lead to cloudy beer as well. 
  • Carboys do tend to be a bit smaller in overall volume and have a tapered neck and this can reduce the amount of wasted headspace. Less headspace and easier ability to release upward out the airlock or blow-off tube means less chance of oxidation. 

For the fermenting buckets

  • Fermenting buckets are more accessible and cheaper to buy. You can get a food-grade one for around $10.00 where a cheap carboy on its own will be around $20 – $40. 
  • They are also easier to handle and carry. They usually always have a built-in handle that you can pick them up and move them if need be. Carboys have builtin handles as well but are not as easy to grasp. 
  • The buckets are easier to clean and store. Where a carboy has that narrow it will be harder to clean and when not in use store. A plastic bucket really has no parts to break, even if you drill holes for an airlock, you can remove it and store it all safely with worry about it breaking. 

What size brew kettle do you need for a 5-gallon batch?

You get the idea right going bigger will make your life easier. You should add about 2-3 gallons of extra capacity for boiling the entire batch in the same pot to avoid boil over.

So for a 5- gallon batch, you would want an 8-10 gallon pot to boil. That is a very large pot and could be costly. This may not be possible if you don’t have that type of pot or the space to boil that much, so you need to take that into consideration as well. 

Remember that you don’t have to boil the full capacity of the brew. You can just add water later in the fermenter. But to do that you will need to calculate for that in the recipe and not forget it. You will also need other pots going as well as that one and don’t want to make a mess or lose any beer. So read here for more details on what pots and sizes are good. 

Phil - BeerCreation

Hey, I'm Phil. I'm passionate about all things beer. I love making it, drinking it and best all, learning about it!

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