Guide to Fermenting in a Corny Keg

When it comes to choosing a fermenter home brewers have a variety of options available to them, ranging from simple plastic buckets and glass carboys to a large selection of higher-end plastic fermenters to the more expensive stainless steel conical fermenters that are similar to what craft breweries use.

One option that many brewers tend to overlook that provides many of the same benefits as the stainless steel conicals is fermenting in a corny keg. Built out of stainless steel and able to hold up high levels of pressure corny kegs make for an ideal fermenter. They provide numerous benefits including the ability to do pressurized fermentation, pressure transfers, reduced exposure to oxidation, and natural carbonation to name a few.

Refashioning a Corny Keg into a Fermenter

One of the great aspects of fermenting in a corny keg (cornelius) is that it does not take much to convert the keg into a fermenter. You do not have to make many adjustments and no high-tech construction or fabrication skills are required.

The following are the steps involved…

Step #1: Source a Corny Keg

Clearly, the first step is to secure a corny keg for fermenting, if you are presently using kegs for serving it is recommended to pick up a new keg as you will be making modifications to it. Corny kegs are quite easy to come by, most home brewing stores carry new and used kegs. I prefer the used kegs as they do just as good of a job as the newer ones but cost significantly less.

There are two main types of corny kegs, pin lock, and ball lock. Either will work fine. I personally have a mismatch of both in my keg collection.

Step #2: Clean the Keg

Reconditioned or used corny kegs need to be cleaned and sanitized prior to being used. It is not uncommon that when you receive your keg that it will still have some of the soft drink it was used to serve still inside. When I started my brewpub we used corny kegs to carbonate and serve the beer from, we purchased well over 100 of them and the majority of them still had soft drinks in the bottom of them.

Take off the lids, posts, dip tubes, and gaskets. In order to get the posts off, you will most likely need a wrench, you can also now buy sockets for a ratchet that are designed to remove both ball lock and pin lock posts. We highly recommend these as they make removing the posts much easier.

Next rinse your keg and all of the parts with hot water. Add your favorite cleaner to the keg and let it soak, also soak all of its parts in either the keg itself or a separate bucket. Give the keg and all of its parts a good scrubbing to remove all of the old debris.

Next, you will want to sanitize the corny keg and its parts in starsan.

Step #3: Modify the Liquid Dip Tube

The next step is to modify the liquid dip tube to make it shorter. This is the longer of the dip tubes that are attached to the posts. It is the serving tube that the beer would typically come out of when the corny is used as a serving vessel. The reason you want to make it shorter is so that it sits above the trub at the bottom of the keg after fermentation occurs; this prevents clogging of the tube during transfer to the serving keg.

Depending on the type of beer you are making will determine how much you want to cut off the bottom of the tube. The best advice is to cut off a little at a time and see if that works for you. Start with cutting off 1 inch, this will work for most styles of beer. If you know you are going to be brewing very hoppy beers with lots of dry hop additions then you might want to try 2 inches in order to keep it above the larger trub line.

For cutting the tub you can use a hacksaw but it is recommended to use a small metal tube cutter. They are inexpensive, work great and make the job very simple.

Another option instead of cutting your dip tube is to pick up a floating dip tube. Floating dip tubes attach to your corny kegs liquid post just like a standard dip tube, but instead of being made all of metal, the majority of it is made of flexible liquid tubing that has a float ball attached near the bottom of it that keeps the line floating at the top of the liquid level and away from your trub. This is a great option because you no longer have to cut up the stainless steel tube that you may need at another time.

Step #4: Blowoff Tube

Just like with any fermenter as the yeast converts the sugars into CO2 you need a way to allow it to escape. Unlike a traditional fermenter, corny kegs do not have a hole to insert an airlock; as a result, you are going to have to create your own which is as simple as attaching a blow-off tube to the gas post and placing the other end of the tube into a bucket of sanitizer.

There are two ways you can do this, for both you will need approximately 3-5’ of gas line.

The first option is to remove the gas post and poppet, then take a Carboy Bung (stopper) size #6 and push it onto the threads on the gas post, next push the gas line into the other end of the bung.

The second and better option is to simply pick up an extra gas disconnect and attach the gas line to it. Place the gas disconnect on the gas post and the other end of the line into the bucket of sanitizer.

Step #5: Jumper

The last part of modifying a corny keg into a fermenter is making a jumper in order to transfer the beer out of the fermenter and into the serving keg. A jumper is simply a small length of liquid beer line (approximately 15 – 18”) that has a liquid disconnect attached to each of its ends. We will discuss how to transfer the beer from the fermenting keg to the serving keg later in this article.

There you have it your corny keg is now ready to be used as a fermenter…

Fermenting in a Corny Keg 
Beer fermenting in a corny keg
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Fermenting in a keg is done the same as fermenting in any other fermenter. Simply add your wort to the keg, pitch your yeast, put the lid on the keg, attach the blow of tubes and you are set to go.

The following are a few tips to get the best results possible….

Tip #1: Keg Gaskets

Make sure that all of the gaskets on the keg are in good shape and not cracked or it can allow for the ingress of oxygen which will create off flavors.  You can pick up new gaskets at any online homebrew shop.

Tip #2: Keg Lube

It is important to also make sure to put keg lube or even vaseline on the lid’s gasket (o-ring), this will ensure that you get a good seal and no leaks.

Tip #3: No Chill

If you prefer to follow the no chill method of cooling your wort, you do not have to leave the hot wort in the kettle to chill, instead since the keg is stainless steel you can rack the hot wort directly over to the keg and let it cool down to pitching temperature there.

Tip #4: Cold Crashing

Cold crashing is very simple when using this method, simply remove the gas disconnect and place the keg in the fridge or keezer for 48 hours.

Tip #5: Dry Hopping

Unfortunately unlike some of the conical fermenters on the market, there is no real way to add your dry hops without risking oxygen exposure. However, there are some ways to reduce the risk.

The first is after adding the hops to the keg and putting the lid back on you can purge it with CO2 in the same fashion you would purge it when using it as a carbonating and serving vessel.

You can also connect your gas and purge the keg with approximately 5psi at the same time you are adding the hops to it. This fills the top space with CO2 and pushes the oxygen out. Most people would then also purge the keg once the lid is back in place.

Lastly, if you have a second corny keg available you can add the hops to it, seal it, purge it with CO2 and then transfer the beer from the first keg over to the new keg filled with the hops.

Tip #6: Taking Samples

Many brewers like to take gravity readings throughout the fermentation process in order to see when the final gravity has been reached or if fermentation has stalled or finished. It is advised not to take the lid off the keg to do this, instead use a picnic tap connected to a liquid disconnect to pull your sample.

Tip #7: Fermenting Under Pressure

Fermenting under pressure is the latest and greatest invention in home brewing at the moment. It is a process that allows you to ferment and naturally carbonate the beer in the same vessel or a separate one if you prefer but in each case without the use of a CO2 tank or adding sugar.

Corny kegs allow you to implement this method with ease, all that is required is a spunding valve. This post on pressure fermentation will explain how it works.

Transferring Your Beer

The last step in the process is transferring your beer from the keg used to ferment to the keg you are going to use to serve your beer from. Previously in this article, we talked about how to build the jumper you will use to transfer with. The following are the steps involved in the actual transfer…

  • As always make sure your serving keg is clean and sanitized.
  • Put the lid on your serving keg
  • Add 3 – 5 PSI to both kegs.
  • Now connect your CO2 tank to the keg you used to ferment your beer, and keep the regulator set at the same 3 – 5 PSI you pressurized both kegs at.
  • Now attach the jumper line you built to the liquid out posts on both of your kegs.
  • Next, simply vent the pressure from the serving keg. This will allow the transfer of beer to start.
  • The easiest easy to vent the gas is to attach a gas in disconnect fitting to the gas in post. Some people also use spunding valves.

If you take your time transferring you will not run into much foam, but as you get near the end of your transfer expect some to come out the gas in post. The transfer should take about 10 – 15 minutes if you take your time with it.

This post has more on transferring beer.

The Final Word

One word of warning I will leave you with is that because of the gasses being created during fermentation a significant amount of pressure is being built up. As a result, it is very important to never ferment in a completely sealed corny keg or any fermenter for that matter, or the pressure is going to build up and has no way to escape which can be very dangerous.

Outside of that, fermenting in a corny keg is an excellent way to brew top-quality beer that will rival any beer you purchase from your local craft brewery.

If you have ever used a corny keg as a fermenter or have questions about doing so let us know in a comment.

P.S. If you would like to get my top 5 recipes from my brewpub be sure to check out my offer to do so on the side of the blog, my gift to you! Cheers, Big Robb.

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