Die Gärung im NC Fass Teil 1: Grundlagen

Fermenting in an NC Keg Part 1: the Basics

In this first of a series of articles about fermenting using Cornelius (NC, or Pepsi) kegs, we will look at the basic process and give an overview of how it works.

In this article I will consider only NC style kegs, although it mostly also applies other varieties of soda kegs including CC and NC jolly kegs.

The NC Keg Fermenter Blog Article Series:
Part 1: The Basics
Part 2: Temperature control
Part 3: Dry Hopping

Pros and Cons of fermenting in an NC keg

Before diving in, let's take a moment to consider why we would want to ferment in a soda keg. The main benefits that come to mind are:

  • They are a durable stainless steel vessel, inexpensive, and widely available new and used
  • There is a wide opening at the top to facilitate dry hopping and cleaning
  • There are two "quick connect" valves built in for liquid and gas
  • Most kegs are pressure rated up to approximately 9 bar; most lids include a built in pressure relief valve
  • They fit in many refrigerators and converted freezers
  • A wide variety of fittings and adapters are available
  • They can serve a double use as serving kegs with a tap system of your choice

Of course they come with some drawbacks as well, here are the ones I am most concerned about:

  • Relatively small volume capacity of 19L, fermentation capacity approx 17L
  • Small outlet valves are prone to clogging with hop particles and trub
  • No yeast dump valve

Frankly I can live without a yeast dump and have found several solutions to prevent clogging, described in more detail in Part 3 of this blog series. As for the volume limitation, I find that fermenting 17l of wort provides me about 15L of finished beer after cold crashing and transferring, which is the perfect amount for me to keep different beers on tap without staling, gaining more brewing experience with more frequent brew days! For the the times I want to brew larger batches, I'll use two kegs for fermenting. That also gives you a chance to experiment with different yeast strains and dry hop profiles with the same wort.

Note: I don't consider the tall and slender shape of the vessel as a negative at the homebrew scale. Large breweries may prefer wider fermenters to minimize the hydrostatic pressure on the wort column when brewing ales, as pressure during fermentation tends to reduce the ester development of the fermenting wort. For a fermenter of this size I can't imagine there are pressure issues.

Recommended Equipment:

Note: we sell new NC Kegs bundled with all the parts you need to make fermentation easy!

When fermenting in a keg, always use a lid with a permanently installed pressure relief valve. If your blow off port gets clogged (rare, but it can happen) dangerous pressure can quickly build up in the keg!

In case you're wondering if you can ferment in a keg without a CO2 tank and regulator, the short answer is yes. But you're going to need to use some tricks to rack the wort or fill your bottles. Place the fermenter up high on a table and connect a tube with picnic tap, bottling wand, or transfer tube that extends below the bottom of the keg. This will allow you to gravity fill once the flow starts. To get the flow started, it helps to have some pressure built up in the keg already. This is best done with a spunding valve before the fermentation ends. Otherwise you will have to use some other siphon starter such as this one or this one. In the end, it is much easier to do by connecting a CO2 bottle to the keg, and I assume most brewers will use that route instead.


1. Clean and disinfect your keg fermenter. If you've purchased a used keg I recommend a complete disassembly and replacing all the o-rings. I clean my kegs using Chemipro Oxi and the Trident Keg Cleaner. You can also fill the cleaning solution in the keg and use a long handled brush to scrub the keg. Don't forget to clean the inside of your dip tubes, there are special brushes available for that too. After a quick rinse I fill the keg with 2L of StarSan to disinfect, close the keg, shake it, and let it rest before dumping it out. Now it is ready to use.

2. Install the floating dip tube in your keg. Actually, do this before disinfecting! This step is actually optional, but I find it is a crucial step to avoid frustration when transferring. For a while I cut the end of the stainless steel liquid dip tube about 3cm shorter to keep it above the yeast cake and prevent clogging. I still had issues with the valve clogging. Since I started using the floating dip tube (see equipment list above) along with a good cold crash I have not had any more clogging problems! Check out the video to see the assembly of a keg fermenter with thermowell and floating dip tube in the lid (sorry only available in German).

3. Fill your fermenter. You can actually fill the fermenter with near boiling temperature wort, but I will assume you've already cooled your wort to near pitching temperatures first. I usually pump the wort into the keg, allowing it to splash in from a height to promote oxygenation. Once I've measured the fill level to 17L, I close the keg and give it a good shake for more oxygenating. If you anticipate a very vigorous fermentation, fill a bit less wort or expect to have some wort pushed out the airlock with the krausen.

4. Next you want to pitch your yeast. If your wort isn't cold enough yet, put it in your fermentation fridge to cool it down first. If you've just finished shaking the wort to help get it oxygenated, it gets pretty foamy so pull the vent open before opening the lid again to pitch your yeast.

5. Place the fermenter in your fermentation fridge and connect the blow off tube. This is usually a simple polyethylene tube connected to a gas disconnect on the gas side outlet of the keg. The other end of your tube goes into a container or water or disinfectant. There is always a chance of the gas valve or tube clogging, more so with a vigorous fermentation and when dry hopping early, so be sure your keg lid has a pressure relief valve built in.

6. Place your chamber temperature probe on, near, or in the keg itself. To accurately control fermentation temperature, you will want to place the probe on the keg and tape a piece of insulation over it. You can use our purpose built insulating sleeve for this as well. For a more comfortable solution, place the probe directly in the keg using the keg thermowell. Read more about temperature control options in part 2 of this blog series!

7. Dry hopping in the keg can be done at the time of your choosing. I used to dry hop in a separate keg after fermentation is complete, but nowadays I typically dry hop near the end of primary fermentation, when there is still enough yeast activity to absorb any oxygen introduced. I like to place the hop pellets in a stainless steel keg hop filter and drop it in the top of the keg while simultaneously purging with CO2 from my tank. The details of dry hopping in a keg go beyond the scope if this article but you can read more in part 3 of this blog series.

Dry hops in a keg filter

Dry hops without keg filter


8. Sample the beer and check fermentation progress. Sampling is done through the liquid out side of the keg. You need pressure in the keg to push beer out. An easy way to do this is disconnect the blow off tube for 15-30 minutes (or less during very active fermentation). Alternatively, if you're spunding at this point, there is already pressure in the keg. You can also just connect your CO2 bottle to the keg and apply a small amount of pressure to allow flow to start, 0.5 bar is more than enough. Connect a piece of hose to a liquid ball lock disconnect and snap the disconnect onto the liquid out valve on the keg. Beer should flow immediately, so be ready to remove the disconnect to stop flow when your sample is done. If beer does not flow, it is possible your intake is clogged in the keg. This happens rarely, when it does you can push gas in the liquid side to help clear the clog. To simplify the sampling process, check out our sample assembly with a picnic tap, or make your own!

9. Spunding (optional). Spunding is the process of fermenting under pressure. Some brewers do this for the whole fermentation period with lager beers styles to suppress esters in the beer. If your goal is simply to capture CO2 and begin the carbonation process, it is sufficient (and arguably better when using an ale yeast) to connect a spunding valve with about 2-3P remaining in the fermentation process. Remove the blow off tube and connect your spunding valve. You will need to adjust it as pressure builds so start with the valve mostly open and close it incrementally, keeping a close eye on it! I like to preset my spunding valve with by connecting it to my CO2 bottle first and use the regulator set to my desired pressure setting. To do it this way, close the spunding valve all the way and open it slowly until you hear CO2 escaping. Now connect it to your keg and it's ready to go.

10. Fermentation complete? Time to cold crash. You really shouldn't skip this step, especially if you want to prevent clogging. I usually set the freezer to 2C and let it sit for at least 24 hours before transferring. This gives enough time to reach the desired temperature and allow particles to settle out. Depending on your cooling capacity you might want to let it rest longer than that before transferring. You can now transfer your beer into a secondary keg, a serving keg, or even bottle it with a counter pressure bottle filler or uncarbonated into bottles for final conditioning.

Without a cold crash, especially when dry hopping without a filter, you will very likely clog the output valve or dip tube. Prevent this by (1) using a floating dip tube (2) dry hopping in a filter and (3) performing a thorough cold crash before transferring.


11. Transfer. I have heard from other users that you can leave the beer on the yeast cake and drink from the fermenter directly, but my experiments with this method didn't work, and I suspect that yeast autolysis was a problem. Nowadays I always move my finished beer to a second serving keg when fermentation is complete. The second serving keg has been completely purged of oxygen using a starsan flush (filling the keg with starsan and pushing it with Co2 into another keg). I like to use a shutoff valve between the two kegs and the spunding valve on the keg being filled to regulate flow into the new keg. Once my serving keg is filled I leave the CO2 connected for another week at cold temperature to mature and ensure it is fully carbonated, even if the spunding valve was used. But I have also gone from grain to glass in 7 days with a spunding valve. It wasn't the best beer ever, but it was drinkable. You can also fill bottles directly from the fermenter: use a simple transfer tube for uncarbonated beer or a counter pressure bottle filler for finished beer.

Tip: you can connect your blow off tube to the liquid port of your serving keg to purge your keg using the CO2 produced during fermentation (see the picture at the top of this article. The blow off tube is connected to the gas out valve of the serving keg. I have opened kegs after doing this to make sure there was no krausen in the serving keg. As long as fermentation is not too wild the serving keg remains clean and purged, and ready to fill

12. Cleanup. For the last step, clean out your fermenter. It's best not to wait too long and let things dry out before washing out your keg. I like to rinse out the keg with warm water then run the keg washer for at least 10 minutes with Chemipro Oxi as soon as the keg is drained.

That's it for now…cheers! Be sure to check out our other blog articles on keg fermentation for more details on temperature control and dry hopping!

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